CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE...

108
CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department of Civil Engineering and Applied Mechanics McGill University Montreal, Canada A thesis submitted to the Faculty of Graduate Studies and Research in partially fulfillment of the requirement for the degree of Master of Civil Engineering September 2003 ® Gang Ye, 2003 All Rights Reserved

Transcript of CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE...

Page 1: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

CARBON DIOXIDE UPTAKE BY CONCRETE

THROUGH EARLY-AGE CURING

By

Gang Ye

Department of Civil Engineering and Applied Mechanics McGill University Montreal, Canada

A thesis submitted to the Faculty of Graduate Studies and Research in partially fulfillment of the requirement for the degree of Master of Civil Engineering

September 2003

® Gang Ye, 2003

All Rights Reserved

Page 2: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Abstract

Due to the anthropogenic activities, the increasing carbon dioxide concentration

in the atmosphere is disturbing the natural equilibrium of the greenhouse gas, and causes

the global temperature rise. In 1990, the CO2 emission from fossil fuel fired power plants

contributed 30% of global emissions. In the same year, the cement industry contributed

about 5% of the total. According to Kyoto Protocol, a tremendous effort is required to

reduce the carbon dioxide emission.

One potential technology in CO2 mitigation responses is the use of concrete

products as carbon sink through the early age fast curing. The cement compounds C3S

and C2S are instantaneously carbonized into calcium carbonate and silica gel, once

cement is mixed with water and exposed to the carbon dioxide gas. If it works, concrete

production lines can be set next to the power plants or cement kilns to produce the

concrete products using the captured CO2 as curing agent.

This thesis reports a feasibility study based on a preliminary work. The purpose of

the research was to find a proper combination of a large number parameters to use

cement, slag or waste cement to sequester CO2 emitted from industrial point sources, and

at the same time to make high performance concrete products. In order to understand the

carbonation curing, this study was directed towards the mix designs, carbonation

conditions and the mechanical properties of carbonated products. More than 40 batches

of carbonated concrete specimens were prepared with the following variables in their

preparation: chemical additive, CO2 concentration, carbonation time, carbonation

pressure, thickness of specimen, and CO2 supply method. The performance of the

Page 3: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

carbonated specimens was assessed through the mass gain, the compressive strength, the

bending strength, the pressure drop, the temperature rise in the curing chamber, the

carbonation depth and the microstructure characteristics. Two-hour carbonated concrete

products can have a strength equivalent to 2-month air curing, and take up 8% carbon

dioxide by weight without special treatment.

Page 4: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Resume

En raison des activites anthropiques, la concentration croissante en dioxyde de

carbone (CO2) dans l'atmosphere destabilise l'equilibre normal de l'effet de serre et

suscite l'elevation de la temperature moyenne globale. En 1990, les centrales alimentees

en energie par des combustibles fossiles ont emis 30% des ejmissions globales de

dioxyde de carbone (CO2). En cette meme annee, l'industrie du ciment a contribue 5%

aux emissions globales de dioxyde de carbone (CO2). Selon le protocole de Kyoto, un

effort considerable est necessaire affin de reduire les emissions globales de dioxyde de

carbone (CO2) dans l'atmosphere.

Une technologie potentielle qui reduirait ces emissions consisterait a utiliser le

dioxyde de carbone (CO2) emis par les usines comme un agent de murissement du beton.

Lorsque le ciment est melange a l'eau et est expose au dioxyde de carbone(C02), les

principaux constituants (C3S et C2S) sont instantanement carbonises en une pate de

silicates de calcium hydrates. Si cela fonctionne, des chaines de production de produits

en beton pourraient etre placees a cote des centrales ou des fours a ciment affin d'utiliser

le dioxyde de carbone emis par ces sources en tant qu'adjuvant de cure.

Cette these est une etude de faisabilite basee sur un travail preliminaire. Le but de

cette etude est de proposer un arrangement de parametres qui maximiserait l'usage du

dioxyde de carbone (CO2) dans la production de produits en beton de qualite superieure.

Affin de comprendre plus amplement ce processus de carbonisation qui accelere la

periode de cure du beton, diverses recettes de beton sous diverses conditions de

carbonisation ainsi que diverses proprietes mecaniques seront etudiees. Divers

111

Page 5: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

parametres seront analyses dans plus de 40 melanges differents de beton tels que : Fusage

d'adjuvants, la concentration en dioxyde de carbone(C02), la duree de carbonisation, la

pression de carbonisation, l'epaisseur des specimens et la methode d'approvisionnement

en dioxyde de carbone (CO2). Les parametres qui permettront d'evaluer la performance

des specimens carbonises seront les changements en masse, la resistance en compression,

la resistance en flexion, les changements en pression, les changements en temperature, la

profondeur de carbonisation et la microstructure du beton. Un beton carbonise pendant 2

heures developpe une resistance equivalente a celle d'un beton non traite apres 2 mois.

Dans un tel cas, le beton traite absorberait 8% par masse de gaz carbonique (CO2) sans

avoir besoin de recourir a aucun traitement special additionnel.

IV

Page 6: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Acknowledgment

The author wishes to thank Dr. Y. Shao for his invaluable guidance,

knowledgeable advice, time and effort throughout this project.

The carbon dioxide carbonation system was installed by John Bartczak. The

author would like to thank John Bartczak and Ronald Sheppard for their help with the

tests.

Page 7: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Table of Content

Abstract i

Resume iii

Acknowledgement v

List of Figures ix

List of Tables xi

Charpter 1 Introduction 1

1.1 Greenhouse gas effect 1

1.2 Sources of carbon dioxide 2

1.3 Mitigation responses to global warming 4

1.4 Concrete as CO2 sink through early age curing 5

Chapter 2 Literature Review 9

2.1 Compacted calcium silicate mortars and powers on exposure to

C02 9

2.2 Rapid carbon dioxide curing for Wood-cement composite 12

2.3 Carbon dioxide curing of waste concrete 14

Chapter 3 Research Obj ectives 16

3.1 Mixture properties and CO2 curing 16

3.2 Experiments for performance evaluation 17

Chapter4 Experimental Program 19

4.1 Carbon dioxide curing setup 19

vi

Page 8: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

4.1.1 Carbon dioxide gas tank 19

4.1.2 Air gas tank 19

4.1.3 Pressure curing vessel 20

4.1.4 Pressure gauge 20

4.1.5 Vacuum pump 20

4.1.6 Regulators 21

4.1.7 Heater 21

4.1.8 Thermocouple 21

4.1.9 Data acquisition system 22

4.1.10 Method of C02 injection 22

4.2 Materials 22

4.2.1 Cementitious binders and sand 23

4.2.2 Additives 24

4.2.3 Fibers 25

4.3 Mix design and specimen preparation 26

4.3.1 Cylinder mix design 26

4.3.2 Plate mix design. 27

4.4 Experiments for performance assessment 30

4.4.1 Mass gain after carbonation 30

4.4.2 Carbonation pressure drop 30

4.4.3 Carbonation temperature rise 31

4.4.4 Measurement of carbonation depth 31

4.4.5 Compression test for cylinder specimens 32

4.4.6 Compression test for plate specimens 32

Vll

Page 9: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

4.4.7 Three-point bending test for plate specimens 32

4.5 Sample preparation 33

Chapter 5 Results and Discussion 40

5.1 Preliminary study with 12mm-diameter cylinder sample 40

5.1.1 Effect of additives 40

5.1.2 Effect of carbonation time 42

5.1.3 Effect of cementitious binder 42

5.2 Plate specimen test results 44

5.2.1 Effect of additives in plate specimens 45

5.2.2 Effect of CO2 concentration 47

5.2.3 Effect of carbonation time 49

5.2.4 Effect of carbonation pressure 50

5.2.5 Effect of specimen thickness 51

5.2.6 Effect of cellulose fibers 53

5.2.7 Effect of binder 53

5.2.8 Continuous supply with 100% CO2 concentration 55

5.2.9 Continuous supply with 25% CO2 concentration 56

5.2.10 Carbonation at continuous CO2 supply with different mix 57

5.2.11 Compressive strength of carbonated plates 60

Chapter 6 Conclusion 80

References 84

Appendix A Tables for Cylinder Test 86

Appendix B Tables for Plate Test 90

Vll l

Page 10: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

List of Figures

Figure 4.1 schematic of setup 37

Figure 4.2 Picture of Setup 37

Figure 4.3 Carbonation depth definition 37

Figure 4.4 Compression test for plate specimens 38

Figure 4.5 Three-point bending test for plate specimens 38

Figure 4.6 Pressure vessel with carbonated sample 39

Figure 5.1 Effect of additives in cylinder specimens 62

Figure 5.2 Effect of sodium hydroxide to cement ratio 62

Figure 5.3 Effect of carbonation time in cylinder specimens 63

Figure 5.4 Effect of cementitious binder in cylinder specimens 63

Figure 5.5 Effect of cementitious binder in cylinder specimens 64

Figure 5.6. Effect of additives in plate specimens 65

Figure 5.7 SEM of batch Bl andB2 65

Figure 5.8 Cross section of Bl, B2, B3 and B8 66

Figure 5.9 Effect of CO2 Concentration 66

Figure 5.10 Pressure drop during carbonation curing 67

Figure 5.11 Effect of CO2 concentration on carbonation temperature 67

Figure 5.12 SEM of batch B20 and B21 68

Figure 5.13 Effect of carbonation time 69

Figure 5.14 Cross section of Bl, B12 and B17 69

Figure 5.15 Effect of carbonation pressure 70

IX

Page 11: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Figure 5.16 Cross section of BIO and Bl l 70

Figure 5.17 Effect of specimen thickness 71

Figure 5.18 Cross section ofBl and B14 71

Figure 5.19 Effect of cellulose fibers 72

Figure 5.20 Effect of binder 73

Figure 5.21 Cross section of B21, B4 and Bl8 73

Figure 5.22 SEM of batch B4 and Bl 74

Figure 5.23 Carbonation at 100% CO2 concentration 75

Figure 5.24 Cross section of B17, B21 and B22 75

Figure 5.25 Carbonation at 25% CO2 concentration 76

Figure 5.26 Cross section of B9, B16 andB20 76

Figure 5.27 Carbonation at continuous CO2 supply of two hours 77

Figure 5.28 Comparison of 2 -hours carbonation curing with 7-day air curing 78

Figure 5.29 Cross section of Mortar B26 andB27 78

Figure 5.30 Compressive strength of carbonated concrete plates 79

Page 12: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

List of Tables

Table 1.1 Contribution of the major radiative gases affecting the

earth-atmosphere energy 2

Table 1.2 Global Energy Consumption by Energy Source and

Equivalent CO2 Emissions (1990) 3

Table 1.3 Distribution of world C02 emission (1990) 3

Table 4.1 Chemical compositions of candidate materials for C02 absorption 23

Table 4.2 Chemical component of calcium hydroxide 24

Table 4.3 Chemical component of sodium hydroxide 25

Table 4.4 Chemical component of calcium oxide 25

Table 4.5 Mix design of cylinder 27

Table 4.6 Mix design of plate specimen 29

XI

Page 13: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Chapter 1

Introduction

1.1 Greenhouse gas effect

Earth's atmosphere acts like a blanket to absorb the sun's solar radiation, which

heats the earth's surface and keeps it warm. The average temperature of the earth's

surface is about 15°C; without the atmosphere the surface temperature of the earth can be

calculated to be -19°C, like the moon's surface. There is no any atmosphere to help the

moon keep its surface warm. Even though it receives the same amount of solar radiation

as the earth, the mean surface temperature of the moon is about -23°C. This atmospheric

phenomenon that causes a +34°C warming of the earth is called the greenhouse gas effect.

The greenhouse gas effect maintains a viable and comfortable condition for the life on the

earth.

Due to human and anthropogenic activities, the increasing carbon dioxide gas

concentration in the atmosphere is currently disturbing the natural composition of the CO2

greenhouse gases. Furthermore, some argue that the atmospheric CO2 increase is causing

a global temperature increase. As the temperature increases, more water vapor, which is

also a greenhouse gas is released into the atmosphere. Most scientists agree that the earth

is warming at a faster rate than at any time in the last 10,000 years, and that this warming

is caused by increasing amounts of carbon dioxide and other greenhouse gases in the

earth's atmosphere. There are many potential effects and consequences expected to result

from a rise in global temperature. The ocean water level is expected to rise and threaten

Page 14: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

many coast cities with floods due to melting glaciers, melting Antarctic ice caps, and the

thermal expansion of the ocean water. In the tropic zone, the desertification is expected to

be a prevalent trend. The impact of global warming on people and nature is severe, and

will disturb the viable and comfortable environment.

Carbon dioxide (CO2) is the dominant greenhouse gas (GHG) resulting from

anthropogenic activities, contributing to 63.9% of the enhanced greenhouse effect. Other

greenhouse gases include methane (CH4), nitrous oxide (N2O), ozone (O3),

chlorofluorocarbons (CFCs), and fluorocarbons (CFs), which are also the results from

anthropogenic activities. The relative contribution of these gases to the climate change is

shown in Table 1.1.

Table 1.1 Contribution of the major radiative gases affecting the earth-atmosphere energy (in 1992 Values) [Halmann,1999]

Gas Radiative

forcing (W/m2) % Effect

C02

1.56

63.6

CH4

0.47

19.2

N20

0.14

5.7

CFC and others

0.28

11.5

Total

2.45

100 Source: IPCC 1995.p. 17

1.2 Sources of carbon dioxide

Starting from the end of 19th century, the predominant energy supply included

coal, fossil fuel, biomass (agriculture and wood), solar energy, and nuclear energy. The

global (annual) energy consumption by energy source for 1990 is shown in Table 1.2.

75% of energy came from fossil fuels, and the total equivalent C02 emissions were 5.6

Giga ton carbon per year. Even though the energy consumption from the use of oil was

over 40%) higher than that from coal, they produced almost the same CO2 emission

amount. This is because the combusting efficiency of oil is higher than that of coal.

2-

Page 15: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Table 1.2 Global energy consumption by energy source and equivalent CO2 emissions (1990) [Halmann,1999] Energy source Coal Oil Gas Nuclear Hydro Biomass Total

EJ/yra

91 128 71 19 21 55 385

%

23.7 33.2 18.4 4.9 5.5 14.3 100.0

GT (C)/ yr" 2.3 2.4 0.9

5.6

%

40.4 42.7 16.9

100.0 a EJ= 1018joiiles b GT (C)/yr = 106 tone of C as C02 per year Source: IPCC 1996. p.83

The distribution of CO2 emissions from different sectors of the world economy is

shown in Table 1.3. In 1990, the CO2 emission from fossil fuel fired power plants

amounted to 30% of global emissions, equivalent to 1.8 billion tons of carbon. In the

industrial sector, the cement industry creates a relatively high concentrated CO2 emission.

It is estimated that the cement industry contributed about 5% to global CO2 emissions,

equivalent to 1100 million tons of CO2 and 300 million tons of carbon [Worrell, E., 2001].

The carbon dioxide emission from the transportation sector was hard to collect and to use.

Table 1.3 Distribution of world C02 emission (1990) [Halmann,1999] Energy-Consuming sector Power and heat generation from industry Transportation Commercial and residential CO2 emission

% of world CO2 emission 47 22 31

5.6GT/yr

In 1996, Canada was the ninth largest country producer of CO2 emissions from fossil

fuels. This amount of carbon dioxide gas from fossil fuel was about 120 million tons. The

cement production in Canada in 1994 was 10 million tons and the corresponding CO2

emission was 8 million tons, an equivalent of 2.2 million tons of carbon. Canada signed

3-

Page 16: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

the Kyoto Protocol and committed the country to work toward the ratification of a

binding target in 2002. The target was to reduce annual GHG emission to a level of minus

6% relative to the 1990 level in the 2008-2012 time frame, which was estimated to have

been the equivalent of 601 Mt of C02 [Mourits, 2001]. According to the standards set by

the Kyoto Protocol, there is a lot of carbon dioxide to be removed, recovered and

disposed of in Canada in the following 10 years.

1.3 Mitigation responses to global warming

Carbon dioxide is the most influential greenhouse gas, so the current research of

mitigating technologies was focused on the CO2 emissions from the use of fossil fuel.

These mitigating efforts included the following [Halmann, 1999]:

• Improve energy efficiency. Improve the conversion efficiencies from fossil

fuel energy to electrical and thermal energy and improve the utilization

efficiencies of the electrical and thermal energy to reduce the CO2 emission.

• Fuel switch. Use natural gas and oil instead of coal to reduce the CO2

emissions.

• Removal, recovery, and disposal of COi. The CO2 emitted from the fossil-

fuel-burning power and engines can be recovered. The gas can also be

disposed into the ocean, land aquifers, depleted gas and oil wells, salt domes,

and natural minerals.

Page 17: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Utilization of COi. The recovered CO2 and collected waste gas from thermal

power plant could be converted into construction materials, or used for

beverage production and industrial chemical manufacturing.

Use non-fossil energy source. Nuclear energy, hydroelectric power plant,

geothermal energy and wind power energy do not release any carbon dioxide.

Solar energy has minimal carbon dioxide emissions.

1.4 Concrete as CO2 sink through early age curing

Studies on capturing and disposing CO2 in oceans, depleted gas and oil wells are

currently ongoing. Furthermore, utilization of CO2 recovered from stack gases has been

explored for urea production [Halmann, 1999] and enhanced oil recovery [Mourits, 2001].

Finding beneficial uses of as-captured or recovered CO2 is challenging and critical to

greenhouse mitigation. One potential technology is to use the captured or recovered CO2

as a curing agent in production of carbonated concrete products. The process is called

curing carbonation.

The curing carbonation process is different from weathering carbonation that

naturally occurs in hardened concrete. Weathering carbonation is well known and has

been extensively investigated. In weathering carbonation, hydration takes place first when

cement is mixed with water and is followed by natural carbonation, a reaction between

the hydration products and the atmospheric carbon dioxide. The weathering reactions of

major hydration products (calcium hydroxide and calcium-silicate-hydrates) are:

Page 18: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Ca(OH)2+2C02 -* CaC03+ H20 ( 1 )

3CaO«2Si02«3H20 +3C02+ -* 3CaC03«2Si02«3H20 ( 2 )

Weathering carbonation of concrete is a slow process, and becomes a concern in steel

reinforced concrete structure since the carbonation decreases concrete pH, which helps

initial corrosion of reinforcing steel.

The underlying principal is that the cement compounds C3S and C2S are

instantaneously carbonized into calcium carbonate and silica gel once cement is mixed

with water and exposed to the carbon dioxide gas. Curing carbonation is an accelerated

curing process that injects CO2 gas into the curing vessel at room temperature, diffuses

the carbon dioxide into the fresh concrete under low pressure, and transforms the gaseous

CO2 into solid calcium carbonates (CaCOs).

3CaO«Si02+3C02+MH20 -* Si02«MH20+3CaC03 ( 3 )

2CaO«Si02+2C02+MH20^ Si02«AtH20+2CaC03 ( 4 )

Equations (3) (4) are the summation of various reactions, e.g. the dissolution of C02(g) to

C02(aq); the reaction of C02(aq) with H2O resulting in the production of H+ and HCO3"

ions, and subsequent reaction of the H+ ions with the 3CaO«Si02 and 2CaO«Si02 to

release Ca2+(aq) and the subsequent reaction of Ca2+ and HCO3" to produce CaC03(s),

which forms the basis for the CO2 sequestration [Bukowski, 1978]. Since curing

carbonation is a highly exothermic reaction, concrete is solidified at a much faster rate

than by steam curing at 75°C. The carbonation products are primarily calcium carbonates

and silica gel (Eqs. 3 & 4). For applications without reinforcing steel, the carbonated

concrete products can increase performance with respect to achieving strength, durability

and stable dimensions, due to the near-complete depletion of calcium hydroxide. It is

most suitable for concrete products, such as blocks and cement boards.

Page 19: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Accelerated C02 curing for cement is not a new concept. Hardening of alkaline

earth hydroxide cements and mortars using their reaction with atmospheric C02 has been

practiced for thousands of years. However, strength development was very slow. In

1970's, a systematic study was carried out at the University of Illinois on the reactivity

and strength development of hydraulic and non-hydraulic calcium silicates activated by

CO2 [Young, 1974]. This technique was introduced to cement-bonded particleboard

production to reduce the press time due to the fast setting in a CO2 rich environment

[Simatupang, 1995]. The world's first CO2 curing production line for cement flake board

was established in Hungary in 1985. However, the high cost of the CO2 gas production

prevented this development from having a wider commercial application.

As concern for the greenhouse gas effects and global climate changes grows, the

interest in using concrete as a carbon sink has been renewed. This thesis will explore the

possibility of implementing accelerated C02 curing of concrete using as-captured and

recovered CO2 from cement plants. The gas from cement kilns (kiln gas) has a high CO2

concentration and could be an excellent curing accelerator for concrete. CO2 curing thus

can make concrete production environmental friendly through the following reaction:

Limestone (CaCOs) -» CaO + CO2 -» Cement -» captured CO2 -» cement +

aggregate + H2O + recovered CO2 -» concrete products with limestone structure (CaC03)

The production line can be set next to cement plants, using the cement produced in the

plant and the CO2 captured or recovered from the same kiln. The technology is also

applicable to the other major control sources such as thermal power plants. Similar

production lines can be established close to the power plant, using fly ash or bottom ash

Page 20: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

generated from coal-burning process and CO2 recovered from the fuel gas to make the

carbonated concrete products.

Page 21: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Chapter 2

Literature Review

Carbonation cementitious system is not a new process; its origins can be traced

back thousands of years. Humans have used alkaline earth hydroxide cement and mortar

as a binder to build structures, which harden due to their reaction with the carbon dioxide

in the atmosphere. Because of the low concentration of CO2 in atmosphere and low

pressure of CO2, the diffusion of CO2 into mortar is very slow. This results in a slow

strength development of the mortar. Since 1970's, researches were conducted in an

attempt to understand the carbonation mechanisms and their applications in fast curing of

cement and concrete products.

2.1 Compacted calcium silicate mortars and powders on exposure to CO2

Bukowski and Berger [1978] of University of Illinois used the C2S, CS and

Portland cement as binder to research carbon dioxide gas curing. The ratio of binder to

sand was one to one by weight, and the ratio of water to binder was by weight was 0.202,

0.206 and 0.191 for C2S, CS and Portland cement, respectively. The mortar was mixed by

hand for approximately 3 minutes and then compacted at 26MPa pressure into 15.9mm in

diameter cylinders approximately 20mm in height. After compaction, the cylinder was

kept in a vessel with 95% relative humidity for 2 hours before carbonation. They also

made calcium silicate powders for carbonation with the same water to cement ratio as the

compact mortars.

- 9 -

Page 22: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

In their research, two kinds of carbonation methods were developed: a dynamic

flow system in which carbon dioxide gas was at atmospheric pressure and flowed through

the reaction vessel at a rate of 1.4 L/min, and a static system in which the gas pressure

was used and ranged from 0.1 to 5.62 MPa over a constant time of 15 minutes.

Immediately after carbon dioxide curing, all these cylinders were tested for their

compressive strengths. Afterwards the broken cylinders were stored for taking scanning

electron microscopy and other further analysis.

For the carbonated cylinders at atmospheric CO2 pressure in a dynamic system,

they found that the percentage of reacted non-hydraulic calcium silicate mortars and

powders increased with time of carbonation over the range of 5 to 1440 minutes. The C2S

had a much higher initial reaction rate than CS. The degree of carbonation for powder

samples was lower than that of compact mortars. This might have been the result of the

gas flow catching the water from the powder during carbonation.

In the static system carbonation method, it was observed that the degree of

carbonation was proportional to the increase of gas pressure. For 15 minutes of

carbonation at atmospheric pressure, the static system looked like it was inhibiting the

carbonation reaction. The compressive strength of the static system cylinders was about

30MPa and 30% lower than that of equivalent test in the dynamic system under the same

gas pressure. The compressive strength of the C2S and portland mortar with 5 minutes of

carbonation was approximately equal to that of Portland cement hydrated under normal

conditions for one day. Bukowski and Berger [1978] also found that the compressive

strength was a function of the carbon dioxide gas pressure, and for portland cement at

0.31 MPa pressure, the mortar reached its maximum compressive strength, while a

10-

Page 23: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

pressure increase from 0.31 to 5.62MPa did not produce a significant increase in

compressive strength.

Another study was carried out by Young, Berger, and Breese [1974]. In their

experiments, the C3S and /3-C2S was mixed with silica sand in a 1:1 weight ratio. Then

water was added to give a water to cement ratio of 0.125, and the mortar was then

compacted at a pressure of 6500Psi (44MPa) into cylinders 3/8 inch in diameter and 3/4

inch in height. To prevent moisture evaporation, their cylinders were kept at 100%

relative humidity for 30 minutes before they were exposed to carbon dioxide gas.

These cylinders were cured with CO2 for 3 to 81 minutes in both a dynamic and

static system, which is similar to that used by Bukowski and Berger [1978]. However, in

the dynamic flow curing, CO2 gas was passed through a saturated Mg(N03)2«6H20

solution to condition the gas to a nominal 50% relative humidity before CO2 was allowed

to slowly flow across the vessel. In the static method, the cylinders were put into a bag

that was then injected with carbon dioxide gas. For long durations of carbonation, the bag

was periodically re-inflated with CO2 to avoid CO2 starvation.

The split-cylinder test was done to determine tensile strengths, and compressive

strengths test was done directly on the uncapped cylinders. They also performed scanning

electron microscope tests to analyze the carbonation.

For the first 10 minutes, the carbonation reaction was rapid and considerable heat

was released. It was clear that significant amounts of water evaporated from the sample in

the static system. The strength was developed quickly in the compact mortars of both C3S

and 18-C2S. The compressive strength of both samples was over 7000Psi (50MPa) after

81 minutes carbonation. They found that the water content was the most important

parameter for the carbonation process, and the distribution of the reaction was not

-11 -

Page 24: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

uniform through the specimen. Most of the reaction took place at the cylinder's surface

while little occurred at the center.

Wagh and Singh [1995] of Argonne National Laboratory also studied carbonation

curing using commercial Type I Portland cement. They mixed the cement with silicate

sand, with the proportion of cement ranging from 100 to 30 %. The mixture paste was

compressed into a cylindrical mold at 2000 Psi (14 MPa). The curing system used was a

desiccator with an inlet and an outlet. Some water was put in the bottom of the desiccator

to maintain the humidity of the C02 gas. After carbon dioxide curing for 30 minutes, the

cylinders were dried at 75°C. They also made reference cylinders cured in air at the same

time, but these cylinders did not set. The compressive strength of the cylinders containing

only cement was 4780 Psi (33.46 MPa), and that of cement concrete (50 % sand) was

2612 Psi (18.28 MPa). The carbonated cement sample almost reached the strength of

regular 28-day-set Portland cement.

2.2 Rapid carbon dioxide curing for wood-cement composite

Simatupang and his research group [1995] developed a manufacturing process for

cement particleboards in order to reduce the press time. First the wood particles were

soaked with water, then added to Portland cement and mixed until it became a

homogeneous mixture. A special stainless steel apparatus was used to do rapid CO2

cement curing. It included three parts: the lower part with a perforated disc and a three-

way valve to apply either vacuum or carbon dioxide pressure, the press sleeve to take up

the moist wood/cement mixture and the piston to compress the mortar. The mixture was

put into the sleeve and compacted slightly by piston. The compaction pressure was 4 MPa.

- 1 2 -

Page 25: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

After the vacuum of 0.1 Bar, carbon dioxide was injected into the specimen. A special

press plated was designed for the C02 injection during compression. This press plate was

installed on both sides of the specimen, so the top and bottom surfaces of each specimen

could be carbonated. The water to cement ratio was varied from 0.1 to 0.6, which took

into account the water absorption of wood. The diameter of specimen was 50mm and the

thickness was about 12.4mm.

The bending strength of the cement particleboards cured under a carbon dioxide

gas pressure of 5 bar was 13.8 MPa, which showed a slightly higher bending strength

than those made at 7 or 9 bar. The bending strength of 28-day conventional steam cured

spruce board was about 14.4 MPa.

They found that higher gas pressure creates a higher maximum hydration

temperature and shorter setting time. But the increase from 7 Bar to 9 Bar did not

apparently increase the carbonation. The water to cement ratio and the porosity were also

important parameters for the carbon dioxide curing. The water to cement ratio should be

high enough to provide sufficient water, but if the ratio was too high, the gas permeability

was hindered to achieve good penetration and carbonation [Simatupang, 1995].

A group from Kyoto University, Japan, also conducted research on cement-

bonded particleboard by using carbon dioxide curing [Hermawan, 1998]. They used three

types of curing methods: C02 gas curing, supercritical CO2 curing, and conventional

curing. The samples were fabricated at a cement/wood particle/water ratio of 2.2:1.0:1.1

by weight. The concentration of CO2 gas was close to 100 %; while the supercritical CO2

concentration was 10, 20, 50, and 100 %. The dimension of the sample was 50 x 210 x 12

mm. After CO2 curing, samples were put in an oven at 80°C for 10 hours, then they were

kept at room temperature prior to property evaluation. The samples were evaluated by

- 1 3 -

Page 26: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

following three tests: three point bending test, internal bond strength, and water

absorption test.

Compared to the conventional curing method, the gaseous and supercritical

carbon dioxide curing significantly increased the mechanical properties and dimensional

stability of the cement-bonded particleboard. The mechanical properties of the particle

boards made by gaseous CO2 were similar to those by supercritical carbon dioxide curing;

although the supercritical C02 curing accelerated the strength development faster than the

gaseous CO2 curing.

2.3 Carbon dioxide curing of waste concrete

Teramura and Isu [2000] interested in the use of waste autoclaved lightweight

concrete (ALC) as binder in carbonation process. The waste ALC were crushed and

sieved to under 1.8 mm and then pulverized by a ball-mill for 60 minutes. The water to

solid ratio was in the range of 25-65% by weight. The wet waste ALC was compacted in

the mold under lOMPa pressure to form the plate 100 x lOOx 12 mm. The carbonation

process used 100% concentration CO2 and gas pressure from atmospheric to 0.4 MPa.

They also experimented atmospheric carbonation by using 3% CO2 concentration and

atmospheric pressure. The carbonated samples were dried in an oven at 60°C for 24 hours

after carbonation. These plates were tested by a three point bending test, at a cross-head

rate of 0.2mm/min.

For the waste concrete, Teramura found that 50% was the optimum water to

cement ratio for carbonation. The highest bending strength was 4.8 MPa. The bending

strength of samples made of waste concrete increased linearly with the carbonation

- 14-

Page 27: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

degree. Also, the strength of fine powder carbonated samples was higher than that of

coarse powder samples at the same carbonation degree [Teramura, 2000].

-15

Page 28: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Chapter 3

Research Objectives

The purpose of this research was to explore the possibility of using as-captured

CO2 or recovered CO2 from point source such as cement kiln in the manufacture of

carbonated concrete products. A preliminary study is reported in this thesis. The goal was

different from the previous work in that the present study in directed towards not only the

early strength development by carbonation, but also the increase of mass gain due to the

carbonation by the cementitious binder. In order to understand the mechanism of the

carbon dioxide absorption by concrete materials, this research was focused on the effect

of the mix design, the carbonation conditions and the properties of carbonated products.

3.1 Mixture properties and CO2 curing

The objective of developing various mixture properties was to examine their

effect on CO2 absorption and early age strength. Chemical additive method was employed

to enhance CO2 absorption. The additives include calcium oxide, sodium hydroxide,

calcium hydroxide. Type 10 portland cement, ladle slag, and waste cement were used as

the binder and the CO2 absorbent in carbonated samples. Cellulose fibers were added in

some batches for better toughness and absorption. And fine sand as filler for mortar batch.

Water to cement ratio of 0.15 was kept as a constant and samples are press formed under

8 MPa pressure.

- 16

Page 29: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

To find the best conditions for the carbonation process, samples were treated by a

variety of combinations of process parameters:

• Concentration of C02: 25%, 50%, and 100%;

• Carbonation time: 5 minutes, 10 minutes, 15 minutes 120 minutes and 180 minutes;

• Carbonation pressure: 2 Bar, 4 Bar, 5 Bar;

• Method of CO2 supply: one-time supply and continuous supply.

25% and 50% concentration were used to simulated the as-received and partially

recovered exhaust gas from thermal power plant or cement plant. The use of 100% CO2

was to mimic the fully recovered gas. This was designed to understand how the

concentration of CO2, the carbonation time, the carbonation pressure and the supply

methods could affect the properties of carbonated samples.

3.2 Experiments for performance evaluation

The following experiments were performed to assess the behavior of carbonate

products:

• The mass gain: The mass of samples was measured before and right after carbonation.

Disregarded the water evaporation, the difference of the mass was the mass gain of

the sample. The actual mass gain could be higher because of the evaporation.

• The pressure drop: The carbon dioxide was sequestered by the cement samples while

the carbonation reaction took place. The pressure drop in the vessel was monitored as

an indicator of the reaction.

17-

Page 30: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

• The temperature rise: The temperature rise of the plate was another indication of

carbonation, which was recorded using thermocouple during the carbonation.

• The carbonation depth: Solution of 1% phenolphthalein was used to determine the

depth of carbonation in comparison with the direct measurement of solid carbonated

skin.

• The flexural and compressive strength: The three-point bending test was done for

determination of flexural strengths of carbonated plates, and the compressive tests for

compressive strength right after carbonation.

• SEM observation: Scanning electron microscope was employed to analyze

microstructure of the carbonation products.

Page 31: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Chapter4

Experimental Program

4.1 Carbon dioxide curing setup

The test setup for carbonation of concrete included carbon dioxide gas tank, air

gas tank, pressure curing chamber, pressure gauge, vacuum pump, heater, thermocouple,

and date acquisition. Figure 4.1 is the schematic of the setup. Carbonation system had

both air and CO2 gas tanks so that CO2 could be diluted to simulate the exhaust gas from

the thermal power plant or the cement plant. The system is shown in Figure 4.2.

4.1.1 Carbon dioxide gas tank

Carbon dioxide gas used in this project was a manufactured gas, compressed in

liquid state and stored in high-pressure tank (Megs Inc.). The purity of carbon dioxide

was 99.8%o. The CO2 in the cylinder of a size 1A weights 27.22 Kg. The cost was

approximately $1.36/Kg.

4.1.2 Air gas tank

Compressed air was stored in high-pressure tank and was used to dilute the CO2 to

achieve low concentration. The air cylinder was supplied by Praxair Canada Inc (product

NO. MSDS# E-6778-D).

- 19-

Page 32: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

4.1.3 Pressure curing vessel

The Model 1500 15 bar pressure plate extractor was the product of Soil moisture

Equipment Corp; this model Pressure Plate Extractor was used as a pressure curing

chamber in a pressure range from -1 Bar to 15 Bar. The pressure vessel was 10 cm (4

inch) deep and had an inside diameter of 30 cm (12 inch). Up to 6 cement plate samples

(127 x 76.2 x 12.7 mm) could be accommodated at one time. The model 1500 consisted

of a pressure vessel and lid, clamping bolts, O-ting seals, and outflow tube assemblies.

4.1.4 Pressure gauge

Pressure gauge was the product of Duro United Instruments. The pressure of the

gauge ranges from -1 Bar (-14 Psi) to 14 Bar (200 Psi) and the precision of this gauge

was 0.2 Bar. The pressure gauge measured the volume of the gas injected into the vessel

and monitored the possible pressure drop during carbonation in one-time supply.

4.1.5 Vacuum pump

This pump was used to generate a vacuum in the curing vessel. This Vacuum

pump was the product by Central Scientific Company. (Catalog No 91308, Serial No.

146). The vacuum was needed when 100% C02 gas was used in carbonation.

20-

Page 33: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

4.1.6 Regulators

Regulators were used in gas delivery system to reduce pressure from high-

pressure source to a safe working pressure for use. There were two regulators in the CO2

curing system. Matheson Inc made both of the regulators for C02 and for Air cylinder.

Each regulator had an inlet gauge and an outlet gauge, the inlet gauge was used to

monitor the source gas pressure and the outlet gauge was used to monitor the outlet gas.

Both of these two inlet gauges had the same pressure range, from 0 to 210 Bar; and had

the same precision 7 Bar. Both of the outlet gauges had the same pressure range from 0 to

14 Bar (0 to 200 Psi), and the same precision 0.35 Bar. It was very useful when a

continuous supply of CO2 or air for the curing chamber was required at a designed

pressure value.

4.1.7 Heater

Because the carbon dioxide was stored in a gas tank in liquid state, it emitted from

the high-pressure tank while absorbing a lot of heat. The temperature of the gas was much

lower than the room temperature. This heater was necessary to warm the Carbon dioxide

from the tank and made sure the gas reaches a room temperature when it passed over the

heater. This heater used power and was also a product of Matheson.

4.1.8 Thermocouple

21

Page 34: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Thermocouple was employed to measure the temperature of the carbonation

reaction between the cement and the CO2 gas. One Type T (copper-constant Nist 1990)

thermocouple with a precision of 0.1 °C was used with data acquisition system.

4.1.9 Data acquisition system

The data acquisition system is the product of Measurement Groups Inc (System

5100). There was 40-s total conversion time per reading. Input channels in each single

scanner were scanned sequentially at 0.04-ms intervals and stored in random access

memory within a 1 -ms window.

The data acquisition operation software was Strain smart Version 2.21.

StrainSmart is a ready-to-use, Window based software system for acquiring, reducing,

presenting, and storing measurement data from strain gages, strain-gage-based

transducers, thermocouples, temperature sensors, LVDT's, potentiometers piezoelectric

sensors, and other commonly used transducers.

4.1.10 Method of C02 injection

Two methods were used to supply gas into the vessel: one-time supply method

and continuous supply method. For one-time supply method, the valve was switched off

when the pressure reached designed value; for continuous supply condition, the valve was

left on when the pressure reached designed value.

4.2 Materials

- 2 2 -

Page 35: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

4.2.1 Cementitious binders and sand

A CSA type 10 Portland cement (PC) was used as the binder in this carbonation

research. Because the content of the tricalcium and dicalcium silicate in type 10 cement

was high, it should have the ability of taking up a significant amount of carbon dioxide.

Actually it is the calcium oxide component in Portland cement that reacts with Carbonate

dioxide in the presence of water. The type 10 cement contains 62.9% CaO and a fineness

of350m2/Kg (Table 4.1).

Table 4.1: Chemical compositions of candidate materials for COi absorption

Portland cement

Ladle slag

Waste cement

Class C fly ash

CaO

62.9

57.0

62.9

24.8

Si02

20.7

26.8

20.7

39.5

A1203

3.7

5.2

3.7

16.9

Fe203

3.0

1.6

3.0

6.4

MgO

4.2

3.3

4.2

6.3

Na20

0.1

-

-

1.4

K20

0.6

-

-

0.53

S03

2.6

1.7

2.6

2.0

The ladle slag was a waste product from steel production. Its chemical

composition is shown in Table 4.1. Since ladle slag's CaO content was very high,

reaching 57% and just a bit less than cement, it was studied for its ability of absorbing

carbon dioxide. Ladle slag was used in some batches to completely replace the cement as

binder.

The fly ash showed a low content of CaO, and was used in hybrid system with

Portland cement in the carbonation test. Fly ash is an effective additive to makes concrete,

more durable and easier to work with.

- 2 3 -

Page 36: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

As shown in Table 4.1, ground waste cement has 62.9% CaO by weight, and

therefore could have ability to sequester the carbon dioxide. The ground waste cement

was obtained through crushing and grinding the used fiber-cement board to a size that is

close to cement.

The fine river sand of a fineness modulus of 2.3 was also used as filler to make

mortar samples.

4.2.2 Additives

Calcium Hydroxide [Ca(OH)2]. Calcium hydroxide can react with CO2 by itself to form

CaC03 and was used as adhesive filler between bricks and stones in the masonry

buildings. Ca(OH)2 reacted with atmospheric carbon dioxide form a durable binder.

Calcium hydroxide was added in the cement paste in the hope to absorb more carbon

dioxide, and help gain higher early strength.

Table 4.2 Chemical component of calcium hydroxide component

Weight(%)

Ca(OH)2

99.6

Chloride

(CI)

0.05

Heavy

Metals

(as Pb)

0.002

Iron

(Fe)

0.01

Magnesium

and Alkali

Salt

0.3

Sulfur

Compounds

(as S04)

0.09

Certified CAS 1305 -62-0 F. W.74.09

Sodium Hydroxide [NaOH]. Sodium hydroxide is an alkaline material. The pH value of

the NaOH aqueous solution is almost 14. The carbon dioxide needs to be dissolved into

water to form HCO3" or C03"2 then react with CaO. The solubility of carbon dioxide in

-24-

Page 37: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

water is very low. However the solubility of carbon dioxide in alkaline solution is much

higher than that in water. So sodium hydroxide (NaOH) was used as an additive to help

carbon dioxide gas to dissolve into water to form CO3"2.

Table 4.3 Chemical component of sodium hydroxide

Component

Weight(%)

NaOH

97.9

Sodium

Carbonate

0.3

Amnonium

Hydroxide ppt

<0.02

Chloride

(CI)

0.001

Potassium

(K)

0.002

Others

<1.78

Certified A.C.S S318 -500 Solid Unl823

-2 Calcium Oxide [CaO]. Calcium oxide can react with CO3" rapidly. In fact it is the main

component in cement that reacts with carbon dioxide. For the same reason as calcium

hydroxide, calcium oxide was added into the cement paste to enhance the CO2 absorption

and promote higher early strength.

Table 4.4 Chemical component of calcium oxide Component

Weight(%)

CaO

97.9

Fluoride (F)

0.3

Loss on ignition

O.02

Certified F.W.56.08

4.2.3 Fibers

Cellulose fibers were supplied by Weyerhaeuser CO. It was hoped the cellulose

fibers would increase the bending strength and ductility of carbonated cement plates and

•25

Page 38: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

also improve the CO2 absorption. The length and density of fibers was 2.3 mm and 4 g/cc

respectively.

4.3 Mix design and specimen preparation

Two specimen geometries were adopted in this study: the cylinder (12 mm in

diameter and 25 mm in height) and the plate (76 mm wide, 127 mm long and 12.7mm

thick). All the specimens were press-formed under constant pressure of 8 MPa.

4.3.1 Cylinder mix design

14 batches cylinder specimens were prepared and their mix design is shown in

Table 4.5. The batch CI was designed as control batch without additive. Because the

solubility of carbon dioxide is higher in sodium hydroxide than that in water, sodium

hydroxide was tried as additive. Batches C2, C3, C4, and C5 were made with different

sodium hydroxide content from 0.1 % to 5.0 %. Compared with batch C2, water to

cement ratio of batch C6 was reduced from 20% to 15% and additive to cement ratio was

increased from 0.2% to 2.4%. Batch C9 was added calcium oxide as additive, in fact the

CaO content was improved in the mixture. Batch C7, C8, CIO, Cll were used ground

waste cement, slag and fly ash to partially or fully replace the cement as binder. The

batches CI2, CI3, and C14 were designed as the same batch C6, but had different

carbonation time or only air curing. All of these cylinders (CI-CI3) were carbonated

under the 100% concentration carbon dioxide gas, 5 Bar (73Psi) pressure, and one-time

-26-

Page 39: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

supply condition. Since specimens were small, it was difficult to measure the temperature

rise.

Table 4.5 Mix design of cylinder

CI C2

C3 C4

C5 C6 C7 C8 C9 CIO Cl l C12

C13 C14

Binder

(g) PC,(50)

PC,(50) PC,(50)

PC,(50) PC,(50) PC,(50) WC,(50) Slag,(50) PC,(50)

PC,(35)+FA,(15) PC,(35)+WC,(15)

PC,(50) PC,(50) PC,(50)

Water

(g) 10 10 10 10

10 7.5 7.5 7.5 10 7.5 7.5 7.5

7.5 7.5

Additive

(g) 0

NaOH (0.1) NaOH(l)

NaOH (1.8) NaOH (2.5) NaOH (1.2) NaOH (1.2) NaOH (1.2) CaO (1.8)

NaOH (1.2) NaOH (1.2) NaOH (1.2) NaOH (1.2)

NaOH (1.2)

Pressure (bar)

5 5 5 5

5 5 5 5 5 5 5 5 5 5

Time (minute)

15 15

15 15 15 15 15 15 15 15 15 30 120

24hours*

*: curing in the air, PC = Portland cement, WC = waste cement, Slag = Ladle slag, FA = Fly ash

4.3.2 Plate mix design

Based on the preliminary cylinder results, the relative large plate specimens with

12.7 mm thick by 76 mm wide by 127 mm long were also tested. The mix designs of 27

batches are shown in Table 4.6 using the combination of the following varied parameters:

additives, binders, carbon dioxide gas concentration, carbonation time, carbonation

pressure, thickness of plate, and gas supply method.

Batch Bl was the control batch: cement plus water with water to cement ratio of

0.15; the compaction pressure was 8 MPa; 15 minutes carbonation at 5 bar pressure with

one-time supply and using 100% CO2 gas.

• 2 7 -

Page 40: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Batches B2, B3 and B8 were experimented with additives: Batch B2 was added

sodium hydroxide, which had a high performance in cylinder test. Calcium hydroxide and

calcium oxide were added to batches B3 and B8 respectively. The additive to

cementitious ratio by weight in B2 was 2.4%, the same as that used in cylinder

experiment. But the ratio in B3 was 7%, which was the maximum among the three

batches; the ratio in B8 was 1.2%. Because too much calcium oxide in the paste resulted

in fast temperature rise, which could generate cracks during carbonation. Therefore the

ratio in batch B8 was limited to 1.2%.

Batches B4, B7 and B15 used ladle slag as the binder to fully replace Portland

cement. The thickness of B15 was only 6.4mm, half of the thickness of batches B4 and

B7, to study the thickness effect. Cellulose fiber was added into the batch B7, to compare

with batch B4.

Batches B5 and B9 had the same mix design as batch Bl. But these two batches

were carbonated under the diluted carbon dioxide gas. The CO2 concentration was 50% in

batch B5 and 25% in B9. The other carbonation conditions were exactly the same as

Batch Bl.

To obtain the relationship between carbonation degree and time, effect of

carbonation time was investigated. Batches B12, B13 and B17 had the same mix design

as batch Bl, but different carbonation time. They were carbonated by 10 min, 5 min and

120min respectively, with the comparison with 15min in Bl. Carbonation pressures were

changed in batches BIO and Bl l . They were 4 bar and 2 bar respectively to again

compare with Bl of 5 Bar.

28-

Page 41: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Two kinds of thickness of plate were used in the experiments. Most plates were

about 12.7 mm thick, except batches B14 and B15. The thickness of specimens in these

two batches was about 6.4 mm to study the full carbonation, if possible.

Table 4.6 Mix

Bl B2 B3 B4 B5 B6 B7 B8 B9 BIO Bll B12 B13 B14 B15 B16 B17 B18 B19 B20 B21 B22 B23

B24 B25 B26 B27

Binder (g)

PC,(240) PC,(240) PC,(224) Slag,(240) PC,(240) PC,(220) Slag,(220) PC,(237) PC,(240) PC,(240) PC,(240) PC,(240) PC,(240) PC,(120) Slag,(120) PC,(240) PC,(240) WC, 240 PC,(240) PC,(240) PC,(240) PC,(240) WC,(165)

PC,(240) PC,(240) PC,(120) PC,(120)

design Water

(g) 36 36 36 36 36 33 33 36 36 36 36 36 36 18 18 36 36 71 36 36 36 36 50

36 36 20 20

of plate specimen Additive

(g) 0

NaOH,(5.8) Ca(OH)2,(16)

0 0

Fiber, 1.7wt% Fiber, 1.7wt%

CaO, (3) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0

Sand,(120) Sand,(120)

Pressure (bar)

5 5 5 5 5 5 5 5 5 4 2 5 5 5 5 5 5 5

3.5 5 5 5 5

5 0 5 0

Time (minute)

15 15 15 15 15 15 15 15 15 15 15 10 5 15 15 120 120 15

120 120 120 180 120

120 7d, air

120 7d, air

Concen­tration

100% 100% 100% 100% 50% 100% 100% 100% 25% 100% 100%, 100% 100% 100% 100% 25% 100% 100% 0 (air) 25% 100% 100% 100% Moist, 100%

0 100%,

0

Supply

one one one one one one one one one one one one one one one one one one

-

Conti. Conti. Conti. Conti.

Conti. 0

Conti. 0

Thickness (mm) 12.7 12.7 13.5 12.2 13.0 12.2 11.5 12.8 12.7 12.7 12.6 12.8 12.7 6.4 6.4 12.7 12.7 13.6 12.7 12.7 12.7 12.6 12.4

12.7 12.7 12.1 12.0

PC = Portland cement, Slag = One = one-time supply, Conti

Ladle Slag, Fiber = cellulose fiber, = continuous supply

-29-

Page 42: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

4.4 Experiments for performance assessment

The following tests and measurements were performed:

4.4.1 Mass gain after carbonation

Mass gain is an important indicator for CO2 uptake. It was calculated based on the

mass measured before CO2 curing and the mass measured right after CO2 curing. The

ratio of the mass increase to the mass of binder is defined as mass gain by the following

Equation:

(Mass) aftC02-(Mass) abfC01

Massgain = ( 5 ) (Mass)binder

The balance with the precision of 0.005g was used to measure the mass of the

cylinder specimen before and after carbonation, and the balance with precision of 0.1 g

was used to measure the mass of plates before and after carbonation.

4.4.2 Carbonation pressure drop

The carbon dioxide is sequestered by the samples while the carbonation reaction

takes place. So the pressure of the gas inside the vessel is a good indicator for the reaction.

The higher the pressure drop, the more likely the carbon dioxide is sequestered. During

the carbonation curing, the pressure of the gas was recorded at 0 minute, 5 minutes, 10

minutes and 15minutes, and more. This pressure drop was measured only for the plates,

- 3 0 -

Page 43: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

because the cylinder was too small to absorb enough gas that could be shown by the

pressure gage.

4.4.3 Carbonation temperature rise

The temperature of the plate was recorded with the thermocouple and data

acquisition system during carbonation. The carbonation reaction is an exothermic process

that emits considerable heat. The curve of temperature vs. time was again an indicator to

show the reaction. A small hole was drilled at comer of the specimen and the

thermocouple was placed inside the hole to monitor the reaction inside specimen.

4.4.4 Measurement of carbonation depth

Carbonation of concrete could be visualized by using phenolphthalein solution.

The phenolphthalein turned the non-carbonated concrete red and remained colorless in

carbonated concrete. A solution of 1 % phenolphthalein in 70% ethyl alcohol was suitable

for determining the depth of carbonation [RIELM, 1994]. The measurement was done on

the breaking cross section right after three-point bending test. The carbonation depth dk is

defined in Figure 4.3.

The carbonation depth was also measured directly from inspection right after CO2

curing. If only the surface was carbonated, the surface skin was solid and the core

remained soft powder. By scraping the soft core, it was easy to determine the thickness of

solid skin. The reported carbonation depth was measured by this scraping method and

confirmed with phenolphthalein solution.

-31 -

Page 44: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

4.4.5 Compression test for cylinder specimens

The compression strengths of carbonated cylinders were evaluated with MTS

testing machine and the load rate was constantly 0.5mm/min till failure.

4.4.6 Compression test for plate specimens

The compression tests for plate were preformed for batches Bl, B17, B20, B21,

B25, B26 and B27. The plate was tested in compression with a compression surface area

is about 127 x 12.7 mm. Compression test was done by MTS machine and the load rate

was 0.5mm/m till failure. The setup is shown in Figure 4.4.

4.4.7 Three-point bending test for plate specimens

Three-point bending tests were conducted to determine the bending strength of the

plate specimen. Here the plates were evaluated as beams on a span of 101.6 mm, with a

beam thickness of 12.7 mm and a beam width of 76.2 mm. Three-point bending tests were

done on MTS machine and load rate was 0.5mm/min till failure. The test setup is shown in

Figure 4.5.

The flexural strength equation is given as follows:

o =My/I=3PL/2bh2 ( 6 )

32-

Page 45: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

where: o = the flexural strength

M= the bending moment

y = the distance from the neutral axis to the bottom of the beam

I = the second moment of area about the neutral axis.

P = the breaking load of the beam

L = the span of the beam

b = the width of the beam

h = the height(thickness) of the beam.

4.5 Sample preparation

Calcium oxide (CaO) and calcium hydroxide (CaOH) were added to the cement in

advance and were mixed with cement in dry condition for one minute. Fine sand and

cement cementitious were initially mixed in dry condition for one minute. Fibers were

then mixed with cementitious while they were added. Sodium hydroxide (NaOH) was

dissolved into water before mix. Water was then added to mix for at least four minutes till

each powder was wetted. This procedure was followed for the cylinder and plate batches.

For the cylinder samples after mixing, the mixture was filled into the special

cylinder mould, use a aluminum bar with a diameter 0.5inch to push and compact the

paste into the small hole by hand till the paste reach the surface of the mould. Then put

the compaction bolt above the paste, in which there six bolts were fixed on a plate. The

fixed compact bolt could distribute the compact load to each sample. MTS test machine

was used to compact samples, which was easy to control the load. The maximum load

-33

Page 46: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

was 6 kN, in another words, for each sample the compaction pressure is 8 MPa. The

maximum load was 6kN for all except batches CI and C2, which were pressed under 1

MPa and 20 MPa compact force. After compaction the height of cylinder was a little bit

smaller than 25.4 mm. After compaction, the mould was supported by two blocks and the

samples was push out from the mould by MST machine.

For the plate samples after mixing, the mixture was measured to keep each sample

the same mass to get the same thickness after compaction. The paste was poured into

mould and was flatted by a soft brush, which was tried to make the up surface and bottom

surface parallel. Then the mould with paste was compacted by MTS machine. The

maximum load was 78kN, corresponding to about 8 MPa. At same time the thickness of

plate reached approximately 12.7mm. After compaction, the plate sample was demolded

and was kept in a Ziploc until the other two plates were finished. In each batch three

samples were tested for average.

After compaction, the mass of each specimen was recorded as mass before

carbonation. For the plate, one sample in each batch was drilled a small 2 mm deep hole

on the edge before mass measured for thermocouple.

As many as 30 cylinders could be carbonated in the pressure curing vessel at one

time. After the vessel was sealed, use the vacuum pump to pull all the air form the vessel.

The pressure gage reading reached -20" Hg. Then the carbon dioxide was injected into

the vessel. After designed time, the pressure carbon dioxide was released, then the mass

of the samples were measured immediately. The mass is called mass after carbonation.

The pressure vessel and three samples are shown in Figure 4.6. The thermocouple

was inserted in one specimen to monitor the temperature. The heater was switched on at

least for 5 minutes before injecting carbon dioxide gas.

- 3 4 -

Page 47: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Two kinds of carbonation environments were adopted for plates: one was the

100% manufactured carbon dioxide (purity 99.5%); and the other was diluted. For the

100% carbon dioxide, the vacuum pump was used to drive the air out off the vessel, and

then inject appropriate carbon dioxide to reach the designed pressure. For the diluted

carbon dioxide, after the vessel was sealed, appropriate air gas was first injected, followed

by an appropriate carbon dioxide gas. For 25 % diluted carbon dioxide, the air gas was

injected into the vessel to reach a pressure of 3.5 Bar, and then carbon dioxide gas was

added to increase the final pressure to reach 5 Bar. The result was a mixed gas mixed gas

with 25% C02 concentration at a pressure of 5 Bar. For the 50% diluted carbon dioxide

gas, the same procedure was followed by injecting 2 Bar air first and them 3 Bar CO2 to

add up to 5 Bar in total. This procedure followed the basic principle: the ratio of gas by

volume at the same pressure equal to the ratio of gas by pressure at the same volume. The

equation can be expressed as:

V , x P , = V 2 x P 2 ( 7 )

Under the one-time supply method, the valve was switched off when the pressure

reached 5 Bar; for continuous supply condition, the valve was left on when the pressure

reached 5 Bar. The reading of pressure gage was recorded at designed time, such as 0-

minute, 5 minutes, 10 minutes, 15 minutes and 120 minutes. At the same time, the data

acquisition system recorded the temperature rise data through thermocouple automatically.

After designed carbonation time, the pressure gas was released and the mass of samples

35

Page 48: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

was measured immediately to get the mass after carbonation. Samples were tested on the

MTS machine right after mass reading.

-36

Page 49: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Thermocouple

Vacuum Pump

Outlet J

II i

To water

Pressure Vessel

sample |n|et

. . . . ' . . . . . . . J . . . . . . . . . . .. \ = ^ Pressure Gauge

p=tx3 Regulator

Heater

Air

CO?

Figure 4.1 schematic of setup

Figure 4.2 Picture of Setup

form a

/ / / / .

§P • / / / / / * > / / / / / / / ,

^ ^ ^ ^

form b ///A

YS^/, Y777>7C/// W/ WMMMMi

/ /

//7A

Figure 4.3 Carbonation depth definition

-37 .

Page 50: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Figure 4.4 Compression test for plate specimens

Figure 4.5 Three-point bending test for plate specimens

- 3 8 -

Page 51: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Figure 4.6 Pressure vessel with carbonated sample

39-

Page 52: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Chapter 5

Results and Discussion

5.1 Preliminary study with 12mm-diameter cylinder sample

The cylinder strength and mass gain were shown in Appendix A. All of these

samples were made in the same condition at 5 Bar pressure 100%, CO2 concentration, and

15 minutes carbonation time except batches CI2, CI3, and CI4.

5.1.1 Effect of additives

The effect of additive on carbonated cylinders is shown in Figure 5.1. The

compressive strengths and mass gain of batch CI, the control, were 1.3 MPa and 1.63%

respectively. The strengths of batch C4 and C9 are 6.0 and 14.7 MPa, and the mass gain

3.72% and 4.28%. It was apparent that the additives were effective in improving the

carbonation degree and the strength. The % increase in strength by NaOH and CaO was

361% and 1031%, if compared to that of control. And the mass gain increased 128% and

163% respectively.

After the compression test, the core of the samples was examined. The core of

batch CI was still soft, only the surface of CI was hardened; however for the batch C4

and C9, not only the surface was solid, but the core of some batches (C4) was hardened as

well. The depth of carbonation in batches with additives was much deeper than that of

control batch, suggesting that the additives were promoting the carbonation.

- 4 0 -

Page 53: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Figure 5.2 shows batches with different sodium hydroxide content. Four different

sodium hydroxide contents, with additive to cement ratio of 0.2%, 2%, 3.6% and 5%,

were tested and compared with the control (CI). With the additive to cement ratio

increased from 0% to 3.6%, the mass gain increased from 1.6% to 3.7%, however the

mass gain was decreased with the increase of the NaOH from 3.6% to 5%.

The similar trend was observed in the cylinder compressive strength. From 0% to

3.6%, of sodium hydroxide to cement ratio, the compressive strength and mass gain

increased accordingly with the sodium content increase. It was noticed that the increase in

mass gain was not proportional to that in compressive strength. For the batches CI, C2,

C3 and C4, the carbonation depth increased with the increase of mass gain and

compressive strength, but the strength of C4 had a sudden a jump from batch C3. This

was because of the different carbonation depth of cylinder. The cylinder looked like

sandwich, outside surface was hardened but the core was still soft. Even the mass gain of

C3 reached 3.0%, which was larger than that of CI, Batch C3 was still a sandwich. So the

compression strength increased very slowly. For the batch C4, even it was not fully

carbonated, it obtained enough hardened skin to take more the compressive load.

For the batch C5 the mass gain and strength were 3.0% and 4.3 MPa respectively,

both were lower than those of batch C4. For the high NaOH ratio, it was not obvious.

Because of the high content of sodium hydroxide, the mixture reacted more with carbon

dioxide in a short time, leading to more evaporation of water during the carbonation in

batch C5 and a mass gain reduction from 3.7% to 3.0%. At the same time, because of the

water evaporation from the cylinder, there was more sodium hydroxide crystallized in the

cylinder, which caused the reduction of cylinder strength.

41

Page 54: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

5.1.2 Effect of carbonation time

Three different carbonation times were tried; 15 minutes, 30 minutes and 120

minutes. They were compared in Figure 5.3 with 24 hours air curing. All of these batches

had same mix design, 2.4% sodium hydroxide to cement ratio, 0.15 water to cement ratio,

which is shown in Table 4.6. The maximum strength of 26.6MPa was achieved in batch

CI3, the minimum strength was 7.4 MPa in batch C6 that was almost the same as the

batch C14. The strength of 30 minutes carbonation (C12) was 11.6 MPa, which was

higher than that of batch CI4. It was shown that the strength of 15 minutes carbonated

samples was close to that of 24 hours air cured samples, The strength of 30-minute

carbonated samples was stronger than the 24 hours air cured specimens.

The maximum mass gain was 11.2% of batch C13 and the minimum mass gain

was 5.1% of batch C6 in the carbonated samples. Actually mass loss of 0.5% was

measured in batch CI4, owing to the water evaporation in the air curing. With the

carbonation time increased, the compressive strength and mass gain also increased. The

compressive strength increase was likely accompanied by an increase in the mass gain.

5.1.3 Effect of cementitious binder

In Figure 5.4, carbonated ladle slag and waste cement were compared with

carbonated Portland cement. Batch C7 was all waste cement and batch C8 was all ladle

slag. It was designed with the same water to cement ratio and the same additive to

cementitious ratio as used in batch C6.

•42-

Page 55: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

While carbonated slag and cement had similar compressive strength of about

7.6MPa, the compression strength of ground waste cement (C7) was 6.3MPa. However

the mass gain of batch C7 was 9.1%, which is much larger than that of batch C6 and C8.

The mass gain of batch C6 and C8 were around 5.1% and 4.8% respectively. Because the

fineness of waste cement was lager than that of ladle slag and cement, the waste cement

cylinder structure was more porous than ladle slag and cement cylinder. This was the

reason that the mass gain of batch C7 was lager than that of batch C6 and C8. It also

explained why the compressive strength of batch C7 was lower than that of Batch C6 and

C8.

Ladle slag performed similarly as Portland cement. Therefore it had high potential

to be used as carbonation binder and carbon dioxide absorber.

Figure 5.5 shows the hybrid cementitious systems, one was 70% cement plus 30%

fly ash (batch CIO), the other one was 70% cement plus 30% waste cement (batch Cll) .

Batch CIO and CI 1 was designed with the same water to cementitious ratio and additive

to cementitious ratio as in batch C6.

Compared with batch C6, which was 100% cement, batch C10 had low

compressive strength and carbon dioxide absorption. The content of Calcium oxide in the

fly ash was much lower than that in cement (Table 4.1). This was possibly the reason why

hybrid batch (C10) with Fly ash was weaker than C6 with all cement.

However, the hybrid mixture of cement with waste cement had a superior

performance. The mass gain of batch CI 1 was 6.7%, which was larger than batch C6 and

was smaller than batch C7 (Figure 5.4) that used all waste cement as binder. But it had a

very high compressive strength 9.3MPa, larger than that of batch C6 (all cement) and C7

(all waste cement). The larger particle size of waste cement increased the porosity of the

- 4 3 -

Page 56: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

paste, which helped the sample to absorb more carbon dioxide. So appropriate hybrid of

waste cement with Portland cement, will increase the ability of carbon dioxide absorption,

and enhance the compressive strength of the carbonated product.

5.2 Plate specimen test results

In the second phase of this project, rectangular specimens with large dimension

were employed. A thickness of 12.7 mm (0.5 inch) was selected to study if total

carbonation along the thickness was possible. This was also intended to simulate the

thickness of face shell in concrete block and the thickness of the mesh-reinforced cement

boards, the two candidate concrete produced that could be made by carbonation curing.

All batches had same specimen dimensions of around 127 x 76.2 x 12.7 mm,

except that batches B14 and B15 were made with a thickness around 6.4 mm. Each

sample was compacted under 8MPa pressure with MTS machine. Water to cement ratio

was kept 0.15 for most batches, except batches B18 and B23. The water to cement ratio

of these two batches was 0.3 because of the coarse particle size and the high water

absorption capacity of the ground waste cement. Twenty seven batches were investigated

with the combination of the following parameters: additive, binder, CO2 concentration,

carbonation time, carbonation pressure, fiber, and thickness. The summary of test results

was shown in the Appendix B.

The mass gain, flexural modulus, MOR and carbonation depth were compared.

The pressure drop and the temperature rise during carbonation were also recorded in

some batches. Scanning electron microscope (SEM) was used to analyze the

.44.

Page 57: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

microstructure of different carbonation produces. Discussions will be focused on the

effect of different carbonation parameters.

5.2.1 Effect of additives in plate specimens

Based on the preliminary cylinder study, Sodium hydroxide, Calcium hydroxide

and Calcium oxide were added as additives into plate batches B2, B3 and B8 respectively

for better CO2 uptake and strength. The results were compared with control (Bl) in the

Figure 5.6. Batch Bl the control for all plate batches with no additive 100% CO2

concentration, at 5 Bar pressure, 15 minute carbonation under one-time supply condition.

As is shown in Figure 5.6, the control batch (Bl) without additives, had the

maximum bending strength of 4.6 MPa after only 15 minutes. However, in Figure 5.1, for

cylinder specimen, the compressive strength of control batch was lower than that of

batches with additive. It seemed that additives did not make the same contributions to the

bending strength as it did to the compressive strength.

The mass gain of B3 with Ca(OH)2 was high, while the other three were about the

same. The additives did not seem to promote more CO2 absorption in plate specimens. In

the cylinder tests (Figure 5.1), the mass gain was higher in batches with additive. This

was possibly caused by size effect and also due to the inaccurate definition of mass gain,

which disregarded the water evaporation.

The carbonation depth was about 60% in batches Bl, B3 and B8, and only 40% in

the batch B2 with NaOH. Sodium hydroxide did not function in plate specimen as well as

it did in the cylinder. This is shown by the SEM pictures taken near the surface of the two

specimens in Figure 5.7. The small white grains in batch Bl were tobermorite, the

-45 -

Page 58: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

carbonation product that provided the interparticle binding enhanced the strength of plate.

They were not seen in batch B2. Obviously the carbonated plates of batch Bl and B2 had

different carbonation quality. The cross sections of these samples coated by

Phenolphthalein solution are shown in Figure 5.8. The dark color was not carbonated,

while the light color showed carbonation. The 15 minutes carbonation made the 12.7 mm

thick specimen a sandwich structure with a soft core.

The flexural modulus of batch Bl was larger than that of batches with additives,

following the same trend as the strength. Because the concrete is a brittle material, the

bending strength of the plate was determined by the bottom surface in tension. But the

compression strength was determined not only by the quality of carbonated surface, but

also by the carbonation depth. The un-carbonated core significantly reduced the

compression strength. This explained why the bending strength in control was higher than

that with additive.

A high CaO to cement ratio of 1.8 % was also investigated. However after 15

minutes carbonation, plates were cracked at a temperature over 60°C on the plates surface.

A higher reaction rate did not allow for the dissipation of heat and introduced the

laminate cracking. This phenomenon needs future study. Considerable heat was generated

rapidly in carbonation due to the addition of CaO, however the mass gain was not

significant. Fast reaction did not produce more solid carbonation.

Since additives did not show significant improvement on strength, flexural

modulus and mass gain during carbonation curing, it was decided not to use the additive

approach in the other plate batches.

• 4 6 -

Page 59: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

5.2.2 Effect of CO2 concentration

The exhaust gas from thermal-power plant or the cement had a CO2 concentration

about 20-25%. The exhaust gas was simulated by a 25% concentration CO2 in this project

to explore the possible application of the exhaust gas in carbonation curing. 50% and

100% concentration were also studied for the purpose to mimic the partially or fully

recovered C02. These batches were carbonated under the conditions of 5 Bar pressure,

one-time CO2 supply and 15 minutes carbonation time.

Figure 5.9, compares batches Bl, B5 and B9 with 100%, 50% and 25% C02

concentration respectively. It was clear that the higher the CO2 concentration, the more

the carbonation, leading to higher strength and modulus, more mass gain and deeper

carbonation depth. For the 25% CO2 gas, the carbonation depth was only about 1.5mm.

The calcium carbonate layer was too thin to bear the bending strength.

The pressure drop was also an indication of the carbonation reaction. Figure 5.10

was the plot of pressure vs. time during carbonation curving. In 15 minutes, the pressure

of batch Bl dropped from 5 Bar to 2.2 Bar; and the drop in batch B9 happened from 5

Bar to 4 Bar. There was much more carbon dioxide gas sequestered in batch Bl than in

B9; and the pressure curve also showed the carbonate rate of batch Bl was high than B9.

This confirmed that the higher CO2 concentration promoted more carbonation reaction.

The pressure curves of batch B16 and B17 are also shown in Figure 5.10. These

two batches were carbonated for 120 minutes; the concentration of batch B16 was 25%

and that of B17 was 100%. After 120 minutes, the CO2 pressure inside the vessel of batch

B16 with 25%, CO2 concentration dropped to 3.8 Bar. It was corresponding to 80 % C02

absorbed by the cement plate during this period. For the batch B16, 100 % concentration

-47-

Page 60: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

batch, the pressure was reduced to 0.2 Bar at the end of 120 minutes curing. This meant

80 % carbon dioxide gas was absorbed during 120 minute curing time. The mass gain of

B16 was 1.2% and that of B17 was 6.5%. Based on these observations, mass gain of the

plate was proportional to the pressure drop. The pressure drop was an indication of the

carbonation.

The tangent of batch B1 pressure curve was around 0.1 Bar/min, and that of B9

was about 0.02 Bar/min. Trends of B16 and B17 curves were both around 0.002 Bar/min

and 0.008 bar/min, the rate of carbonation was very slow after 120 minute because of the

decreasing of concentration of CO2 in this one-time supply method.

Figure 5.11 shows carbonation temperature curve of batch B16, B17, B20 and

B21. The CO2 concentration in batches B16 and B20 was 25%, and that of the B17 and

B21 was 100%. It was very clear that the maximum carbonation temperature was related

to the CO2 concentration. B17 and B21 had almost the same peak temperature, which was

over 50°C. It was much higher than the peak temperature of 35°C generated in B16 and

B20. For batch B16 and B20, the temperature drop was slow and at 120 minutes the

temperature was still over room temperature. This meant after temperature peak, the

carbonation reaction between CO2 and cement continued. This was why the temperature

curve of carbonation reaction was unlike that of hydration reaction, of which temperature

dropped quickly after peak. This was in accord with the CO2 pressure drop. The same

trend was found in batch B17 and B21, but the temperature of 100%, CO2 batches was

totally over that of 25%, CO2 batches at any time. The temperature curve was another

indication of the carbonation reaction.

•48-

Page 61: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Typical SEM pictures near surface in batches B20 and B21 are displayed in

Figure 5.12. The white grains are the tobermorite, the carbonation product. A large

number of white crystal grains were dispersed within the sample in batch B21. However,

only a few white grains tobermorite were observed inside of batch B20 with 25%

concentration.

As is noticed, the concentration of the carbon dioxide is an important parameter

for the CO2 curing. The increasing of CO2 concentration results in higher carbonation

degree of cement, more mass gain, and a stiffer and stronger material.

5.2.3 Effect of carbonation time

Four different carbonation times were experimented in batches Bl, B12, B13 and

B17 with the time of 15 minutes, 10 minutes, 5 minutes and 120 minutes for each

respectively. The other conditions were kept the same for comparison: 5 Bar CO2

pressure, one-time supply and 100% CO2 concentration.

As is shown in Figure 5.13, 120 minutes curing produced a carbonated product

with more than doubled mass gain and full carbonation along the thickness. 15 minutes

carbonation generated a strength close to that by 120 minutes, but mass gain was only

one-half and carbonation depth of 62%. There was a significant increase in bending

strength between 10 minutes and 15 minutes. With increase of the carbonation time, the

mass gain of plate also increased.

The relationship between the carbonation depth and carbonation time was similar

to that of mass gain. The longer the carbonation time, the deeper the carbonation depth.

The carbonation depth of B17 was total thickness of the plate. The Figure 5.14 shows the

-49 -

Page 62: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

cross section of the B12, and B17 together with control Bl. The dark color was indicative

of no carbonation, and the light color implied carbonated product. Although 120 minutes

carbonation produced all solid sample, there were dark spots on the surface of B17 that

were not carbonated during CO2 curing process. It was clear that the carbon dioxide gas

took time to penetrate the skin to harden the core and 120 minutes was adequate for full

carbonation through the entire 12.7 mm thickness under the 5 Bar pressure.

The flexural modulus of the four batches were all around 2.0GPa. With the

reference to Figure 5.9, the carbon dioxide concentration had more direct effect on the

flexural modulus. This was why the bending strengths of Bl and B17 were close to each

other. Because the carbonation depth in batches B12 and B13 was not enough to bear

high bending load, even it had a considerable flexural modulus, the bending strength of

B12 and B13 was relatively low.

5.2.4 Effect of carbonation pressure

The carbonation pressure is an important parameter of the carbonation curing

procedure. Three batches, Bl, BIO and Bl l , were experimented for the different CO2

pressure at 5 Bar, 4 Bar and 2 Bar, with other conditions kept the same: 15 minutes

carbonation, one-time gas supply and 100% CO2 concentration. The carbonation pressure

was intentionally kept low to make the process practically feasible.

The results are presented in Figure 5.15. The bending strength of Bl was twice as

high as that of batches BIO and Bl l . The bending strengths of BIO and Bl l were only

around 2.2 MPa. However the flexural modulus of batch BIO was close to Bl, and higher

than that of Bl 1. The mass gain was increased with the increase of carbon dioxide gas

-50 -

Page 63: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

pressure. The mass gain of batch Bl, BIO and Bl l was 3.8%, 3.4% and 2.4%

respectively. For the carbonation depth of plate, the higher the carbonation pressure, the

deeper the carbonation depth. The pictures of carbonation depth for BIO and Bll are

shown in Figure 5.16, the dark color of the cross section was hydration, and the light

color was carbonated cement.

In Figure 5.15, for the flexural modulus, there was not apparent difference

between 4 Bar and 5 Bar pressure. But for the strength, mass gain and carbonation depth,

the 5 Bar pressure produced better results than the 4 Bar pressure. It indicated that 4Bar

gas pressure had the similar ability as 5Bar pressure to carbonate the cement. It also

showed an increase in the degree of carbonation as the carbon dioxide pressure was

increased.

It is suggested that properly increasing the CO2 pressure in the curing vessel could

be an alternative method to enhance the carbonation if the other methods turned out to be

ineffective.

5.2.5 Effect of specimen thickness

The major concern of carbonation for commercial applications is the non-uniform

carbonation through the thickness. This also limits many potential concrete products to be

processed by carbonation. In this study, 12.7 mm and 6.4 mm thick specimens were

selected. 12.7 mm sample was to simulate the block face shell and the cement board,

while 6 mm to exam the condition for full carbonation. Batch Bl and B14 were cement

plate, batch B4 and B15 were ladle slag plate. The thickness in Bl and B14 was 12.7mm,

and the thickness in batch B14 and B15 was 6.4mm. The other conditions were the same:

-51 -

Page 64: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

15 minutes carbonation, 5 Bar pressure, one-time gas supply and 100% CO2

concentration. The results are shown in Figure 5.17.

The bending strength of Bl was 4.6MPa, close to that of B14. However the

flexural modulus of the thin plate was much higher than that of thick plate. The modulus

of B14 was almost twice as high as that of Bl. Not only the modulus of thin plate was

higher, the percent mass gain was also enhanced in thin plate, so was the carbonation

depth. This was all probably owing to the full carbonation in thin plate, (see Figure 5.18).

Similar trend was observed in ladle slag samples. The bending strength of B4 was

2.1 MPa, and that of B15 was only 1.2MPa. The modulus of B15 was 3.1GPa which was

over two time of that of B4. The mass gains of batch B4 and B15 were almost the same.

Slag plates with 12.2 mm and 6.4 mm thickness were fully carbonated and all solid across

the entire section.

For the flexural modulus of both cement and ladle slag plates, the thin plate had

higher value than the thick plate. It seemed that more carbonation took place in thin plates

than that in thick plate. The quality of carbonates in thin plate was better than that of thick

plate. Figure 5.18 compares the fully carbonated thin plate with thick one.

The bending strength and the flexural modulus of cement specimens were high

than those of ladle slag plates. However ladle slag plate had higher mass gain and deeper

carbonation depth than those cement plat. Compared the cement plate and ladle plate, the

content of CaO in the ladle slag was relatively high. Therefore ladle slag could be used as

a candidate for hybrid binder system, for Carbon dioxide curing.

It is suggested that reducing the thickness would be a good method to make the

product fully carbonated. Reducing the thickness of samples results in a higher

carbonation degree and better mechanical properties.

- 5 2 -

Page 65: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

5.2.6 Effect of cellulose fibers

Cellulose fibers are commonly used in cement fiberboard for strength and

toughness. In this study, cellulose fibers were employed also for CO2 uptake. The

cellulose fiber was tried with two binders, cement and ladle slag. The weight ratio of

cellulose fiber to cement or ladle was 1.7%. Batch B6 was the cement with cellulose fiber

and B7 was ladle slag with cellulose fiber. Batches Bl and B15 were control batches for

comparison. The other conditions were kept the same: 15 minutes carbonation, 5 bar

pressure, one-time gas supply and 100% CO2 concentration.

From Figure 5.19, it was obvious that small quantity of cellulose fiber did not

significantly improve the bending strength, flexural modulus, and carbonation depth of

the cement and ladle slag plate. A trend was noticed in mass gain. With the help of

cellulose fibers, CO2 uptake seemed to be a bit higher. This phenomenon is worthwhile

further study, since other studies pointed out cellulose material could be a good CO2

absorbent.

5.2.7 Effect of binder

Three binders were investigated in this study for their abilities to take up CO2 and

develop strength through carbonation. They were Portland cement, ground waste cement

and ladle slag. In Table 4.1, type 10 Portland cement has 62.9% of the Calcium Oxide the

effective chemical part for carbonation. The ground waste cement and ladle slag showed

- 5 3 -

Page 66: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

57 % of Calcium Oxide, and were both waste materials. Batch B4 was designed for ladle

slag plate, and Batch B18 was for ground waste cement plate. The mix-design of B4 was

the same as that of Bl, They has the same water to cementitious ratio. However the water

to cementitious ratio in batch B18 was 0.3. This was because the coarse ground waste

cement had a higher water absorption than cement and ladle slag. The other conditions

were the same, which include 15 minutes carbonation, 5 bar pressure, one-time gas

supply and 100% CO2 concentration.

As shown in Figure 5.20, the cement plate had the highest bending strength and

flexural modulus. The ladle slag had the maximum mass gain and carbonation depth. The

bending strength of waste cement (B18) was only 1.3MPa, and strength of ladle slag (B4)

was 2.1 MPa. Compared with cement plate, the bending strength of ladle slag and ground

waste cement was really low. The flexural modulus of batch Bl, B4 and B18 was

2.4MPa, 1.4MPa and l.lMPa respectively. It followed the trend in bending strength. The

trend of mass gain between the Bl and B4 was inversely proportional to the bending

strength. The carbonation depth in the ladle slag plate was the whole thickness, the depth

of the other two was only 62% and 35%. The carbonated cross sections of Bl, B4 and

B18 are shown in Figure 5.21. The ladle slag plate was easy to be carbonated, but did not

have the same microstructure as the cement plate, as is shown in the Figure 5.22. There

were more white grains carbonation products (tobermorite) in the batch Bl near the

surface than in slag sample (B4). This explained why the bending strength and flexural

modulus of ladle slag were lower in slag plates than in cement plates, even slag absorbed

more CO2 and had fully carbonated cross section.

It is conclusive that, although mechanical properties of carbonated ladle slag were

not as good as the cement, the ladle slag had shown considerable ability to absorb the

-54 -

Page 67: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

carbon dioxide gas. It maybe used as carbon dioxide sink for the environment. Ground

waste cement did not seem to be proper for serving as a structure material by itself.

5.2.8 Continuous supply with 100% C02 concentration

It was noticed in the experiments, that there existed CO2 starvation, indicated by

the pressure drop, in one-time CO2 injection method. To enhance the CO2 uptake,

continuous CO2 supply method was therefore adopted. Figure 5.23 compares the results

of 120 minutes one-time supply carbonation with that of 120 minutes as well as 180

minutes under continuous CO2 supply condition, tested under 120 minutes carbonation

with one-time gas supply. Batch B21 was 120 minutes carbonation with continuous gas

supply. Batch B22 was 180 minutes carbonation with continuous gas supply. The other

conditions were kept the same: 5 Bar pressure, 12.7 mm thickness and 100% CO2

concentration.

It was surprised that under the one-time supply curing condition, the bending

strength developed in 120 minutes carbonation (B17) was almost the same as that from 15

minutes curing (Bl), although the mass gain of B17 was much high than that of Bl, since

batch B17 was fully carbonated. Even the carbonation time of B17 was 7 times over that

of Bl, the bending strength and modulus of were close in both batches. The increase in

carbonation time did increase the carbonation depth and mass gain, but did not improve

the bending strength and modulus. Because the pressure of the gas decreased with the

time elapsed, the low carbonation was not efficient at all.

For the 120 minutes and 180 minutes continuous supply, batch B21 and B22 had

almost the same bending strength, flexural modulus, mass gain and full carbonation depth.

- 5 5 -

Page 68: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

It was evident that 120 minutes would be enough to fully carbonate 12.7 mm cement plate.

The cross section of samples was shown in Figure 5.24. The quantity and size of the

uncarbonated dark spots were much larger in B17 than in B21 and B22. It was hard to

find uncarbonated spots in batch B21 and B22. The continuous supply method really

improved the quality and degree of carbonation.

The bending strength generated by continuous supply method (B21 and B22) was

higher than that by one-time supply (B17). The modulus of one-time supply batches was

only half of that by continuous supply. However the mass gain of batch B17 was close to

that of continuous supply produced samples. The three batches were all fully carbonated.

The scratched on specimen surface in Figure 5.24 were made right after carbonation and

were indicative of hardness of the carbonated solids down to the core. The continuous

supply method provided a constant gas pressure and a constant CO2 concentration

gradient in carbonation curing and promote CO2 uptake.

5.2.9 Continuous supply with 25% CO2 concentration

Because the CO2 concentration of exhaust gas from thermal power plant or

cement kiln was about 25%, the diluted CO2 was used to simulate to the exhaust gas.

Different carbonation time for diluted Carbon Dioxide gas was experimented as shown in

Figure 5.25. Batch B16 was 120 minutes carbonation and one-time gas supply; Batch B20

was carbonated 120 minutes in continuous gas supply; these two were compared with

batch B9, which was 15 minutes carbonation and one-time supply. The other conditions

were the same: 5Bar pressure, 12.7 mm thickness and 25%, CO2 concentration.

56-

Page 69: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

The bending strength of batch B16 was 1.7MPa; the flexural modulus was l.OGpa;

the mass gain was 1.2% and the carbonation depth was 25%. All of these attributes were

higher than that of B9, because of the longer carbonation time. On the other hand, the

pressure and concentration of C02 decreased with the time elapsed, and the ability to

carbonate the binder was reduced (Figure 5.10). Due to the limit of the one-time supply

method, the contribution of 120 minutes carbonation was not significant.

However, for the continuous supply method, the bending strength of B20 doubled

that of one-time supply (B16). The flexural modulus of B20 was more than three times

higher than that of B16 and B9. The similar trend was observed in the mass gain and

carbonation depth increase. Compared with one-time supply method, the continuous

supply method is efficient to make high quality carbonated product. But if compared with

B21, which was totally solid after 120 minutes carbonation, B20 was only carbonated

34%. The 25% CO2 concentration in B20 was too low to make the core exposed to CO2.

The gradient line of the carbon dioxide did not reach the core of the plate. The chemically

treated cross sections B9, B16 and B20 are shown in Figure 5.26. It was clear that the

continuous supply method did help carbon dioxide to penetrate the surface of plates and

improve the carbonation degree, even with 25% CO2 concentration.

5.2.10 Carbonation at continuous CO2 supply with different mix

Based on the previous discussion, the continuous supply method with 120 minutes

curing seemed to be an effective method for the cement plate carbonation. More batches

were studied under different conditions. Batch B21 was cement plate, carbonated under

dry CO2 condition as was used so far. Batch B24 was the same batch as batch B21 except

-57-

Page 70: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

that moist C02 was used. The moist CO2 was obtained by using water to fill the vessel

under the specimens to increase the relative humidity for carbon dioxide gas. It was

hoped the moist CO2 could promote more carbonation reaction. Batch B26 was mortar

with sand at one cement to one sand ratio, and was carbonated under dry carbon dioxide

gas. Batch B23 was ground waste cement plate, and was carbonated under dry carbon

dioxide gas in 120 minutes under continuous CO2 supply. Batch B21, B24 and B26 had

the same water to cement ratio, and B23 required more water to keep consistency. The

other conditions were the same: 5 Bar pressure, 12.7 mm thickness, continuous CO2

supply method at 120 minutes and 100% CO2 concentration.

In Figure 5.27, batch B21 serves as reference for comparison. B24 with moist CO2

obtained only 5.1 MPa, lower than B21 with dry C02. However, B21 and B24 had almost

the same flexural modulus, the same mass gain and both were fully carbonated.

Carbonation could not take place in the absence of water, but the high relative humidity

environment did not enhance the reaction. Other methods should be explored to damp the

C02 gas.

The bending strength of mortar plate was 6.2 MPa, and the mass gain was high

that reached 7.9%. Mortar plates were totally carbonated. It was interesting to compare

batch B26 with B27, which was cured seven days in the air and had the same mortar mix-

design as B26. It is shown in Figure 5.28, the bending strength and flexural modulus of

the 120-minute carbonation paste (B21) were both higher than those of the same paste

cured 7 days; the bending strength of the 120-minute carbonation mortar (B26) reached

93% of the same mortar cured 7 days in the air, and the same flexural modulus of 2.4 GPa.

The mortar mix with sand was porous if compared to the cement paste mix. It was this

high porosity that allowed more CO2 penetration, leading to a high mass gain in B26. The

-58 -

Page 71: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

cross section of B26 and B27 is shown in Figure 5.29. These cross sections were treated

by phenolphthalein solution, which changed the hydrated concrete to red. It was clear that

the carbon dioxide hardened the whole mortar plates in batch B26. The section of batch

B27 was almost fully covered by dark color, indicating non-carbonation.

If compared to paste and mortar (B21, B24) at 120-minute carbonation at

continuous supply (Figure 5.27), the ground waste cement in batch B23 was not well

carbonated. The strength was low and carbonation depth was only 45%. If compared with

B18 carbonated only 15 minutes at one-time supply, B23 was much better in bending

strength, flexural modulus, mass gain and CO2 absorption. The long time carbonation and

continuous CO2 supply helped the ground waste cement to gain more performance.

Batch B19 was another control to compare with carbonated plates. Specimens

were cured in the vessel at 3.5bar pressure with only air. No CO2 was injected. After 120-

minute in the vessel under pressure, specimen were tested. Batch B19 had a bending

strength of 0.4 MPa, a flexural modulus 0.4 GPa, and a mass gain of -0.3%. The slight

strength gain was obtained through 8MPa compaction. This test was to show that the

early strength development in carbonated plates was truly due to the reaction between

carbon dioxide gas and cementitous material.

Figure 5.11 exhibits the carbonation temperature curve. There was no big

difference between the continuous supply and the one-time supply methods. Zig-zag

waves in the curve of 25% and continuous supply test was observed. The local drop of the

temperature implied a pressure loss and carbonation reaction was slowed down; for a

considerable time, the system detected the pressure drop and automatically injected CO2

into the vessel; resulting in an increase in carbonation reaction and a temperature rise seen

-59 -

Page 72: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

as the peaks. Even the temperature of B20 was not much higher than that of B16, the

continuous gas supply method did help cement plate to sequester more carbon dioxide gas.

5.2.11 Compressive strength of carbonated plates

Compressive strength of carbonated 12.7 mm plates was indicative for the

concrete block application. A few typical batches were chosen for the compressive tests.

They included Bl, B17, B20, B21 and B26.

Figure 5.30 compares compressive strengths at different age: one was right after

carbonation and the other was tested 2 months after carbonation for long term strength.

They were tested in a setup shown in Figure 4.5. Batch Bl was almost the same

compressive strength as B20. Batch Bl was carbonated under 15-minute with 100% CO2

concentration and under one-time supply condition. B20 was carbonated under the 120-

minute using 25% CO2 gas and continuous supply method. The bending strength of Bl

was 4.6 MPa, and that of B20 was 3.5 MPa (See Appendix B). Both compressive

strengths of Bl and B20 right after carbonation satisfied the Building Code for Masonry

blocks. Therefore it is possible to use carbonation method to produce blocks.

The compressive strength was very high in the batches B17 and B21, both of

which were over 50 MPa. The carbonated mortar was also tested. Its compressive

strength was 42.3 Mpa, with a sand to cement ratio of 1:1. All of the five batch

concretes showed sufficient strength for fast production of concrete blocks.

These five batches were tested again after two months of carbonation. Their

compressive strength are also shown in Figure 5.30. After two months, the compressive

strength of Bl was increased to 29.5 MPa. Since Bl cement plate only partially

-60-

Page 73: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

carbonated; after two months, the uncarbonated core was hydrated to develop

additional strength. The batch B20 obtained a much higher strength gain. However

batches B17, B21, and B26 were quite different. Since B17, B21 and B26 were almost

fully carbonated and gain all solids across the section during CO2 curing, there was no

additional strength gained from hydration after the carbonation. In fact, the

compressive strengths of the plates tested right after carbonation were higher than that

after 2 months. This explained why the compressive strength in two months after

carbonation was not higher than that just carbonation. Even the strength was slightly

decreased, the compressive strengths of B17, b21 and B26 were still strong enough for

concrete blocks. On the other hand, the air cured paste (B25) and the cured mortar

(B27) demonstrated a two months compressive strength of 45 Mpa. It was conclusive

that 2-hours continuous supply curing could produce a concrete with properties

comparable to the same concrete air-cured in 2 months; the partially carbonated

concrete products, either at 15 minutes carbonation or with 25% CO2 concentration,

still could develop full strength during secondary curing.

61

Page 74: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

10

5

1 4 7

0 no additive (C1)

SNaOH(3.6%)(C4)

• CaO ( 3.6%) (C9)

Cylinder (r=12.7mm,h=25.4mm), Compaction=8 MPa; C02 pressure=5bar

4 28 3 7 2

Strength(MPa) Mass Gain(%)

Figure 5.1 Effect of additives in cylinder specimens

2

0NaOH(O%)(C1) E3NaOH(0.2%)(C2) El Na0H(2%) (C3) 0NaOH(3.6%)(C4) 0 NaOH(5%) (C5)

6 0

4 3

Cylinder (r=12.7mm,h=25.4mm), Compaction=8 MPa; C02 pressure=5bar

Strength(MPa) Mass Gain(%)

Figure 5.2 Effect of Sodium hydroxide to cement ratio

-62

Page 75: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

30

25

20

® 15

10

26.6

11.6

Cylinder (r=12.7mm,h=25.4mm), Compaction=8 MPa; C02 pressure=5bar

Q15 min Carbonation (C6) a 30 min Carbonation (C12) 0120 min Carbonation (C13) CI 24 hours Air curing (C14)

80

11.2

Strength(MPa) MassGain(%) -0-5

Figure 5.3 Effect of carbonation time in cylinder specimens

0) ~o rj E 5 o> ra

4

3

2

Cylinder (r=12.7mm,h=25.4mm), Compaction=8 MPa; C02 pressure=5bar

74 11

a PC(C6)

SWC(C7) BSIag(C8)

Strength(MPa) Mass Gain(%)

Figure 5.4 Effect of cementitious binder in cylinder specimens

63

Page 76: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

12

10

CD "D 3

c 6

Cylinder (r=12.7mm.h=25.4mm), Compaction=8 MPa; C02 pressure=5bar

13 100% PC (C6)

• 30%FlyAsh(C10)

• 30%WC(C11)

5 1

s-Jl

6.7

Strength(MPa) Mass Gain(%)

Figure 5.5 Effect of cementitious binder in cylinder specimens

64-

Page 77: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

c 3 Dl

4.6

C02 time=15min Pressure=5bar Concentration=100% One supply

3.0

J t

2.3 2.4 2.4

;

LJ

2.1

1.5 1.2

4.9

3.8 3.6

_M

^ N o additives (B1) DNaOH (B2) 0Ca(OH)2(B3) BCaQ(B8)

3.3

0.62 0.62n 6 ".40^-

MOR(MPa) Flexural Modulus(GPa)

Mass Gain(%) CaC03 Depth (x100%)

Figure 5.6. Effect of additives in plate specimens

Batch Bl Batch B2

Figure 5. 7 SEM of batch Bl and B2

65

Page 78: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Batch Bl

Batch B2

Batch B8 Figure 5.8 Cross section ofBl, B2, B3 and B8

0) •a

£3

4.6

Q100%CO2(B1)

Q50%CO2(B5)

Q25%C02(B9)

C02 time=15min Pressure=5bar

One supply

3.8

2.4

1.6

0.8

1.2

'\W\ 0.7

1.3

0.8 0.62

0.24 0.12

MOR(MPa) Flexural Modulus(GPa)

Mass Gain(%) CaC03 Depth (x100%)

Figure 5.9 Effect of CO2 concentration on properties

66

Page 79: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

100% C02, 15min(B1) 25%C02, 15min(B9) 100% C02, 120min(B17) 25%C02, 120min(B16)

40 _ 60 80 Time, (minute)

120

Figure 5.10 Pressure drop during carbonation curing

60

50

O 40

30

20

10

B21. 100% dry C02, continuous supply

\ / B17, 100% dry C02, one-time supply

0 1000 2000 3000 4000 5000 6000 7000 8000 Elapse Time (second)

Figure 5.11 Effect ofC02 concentration on carbonation temperature

67

Page 80: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Batch B20 Batch B21

Figure 5.12 SEM of batch B20 and B21

68

Page 81: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

6

3 4 =>

2

4.9 4.6

0120 min (B17)

S15

• 10

0 5

min (B1)

min(B12)

min (B13)

6.5

2.6

2.0

2.4

2.0

^ « - - - v .

2.0 1.7

3.8

Pressure=5bar Concentration=100%

One supply

3.5

1 1-.-.-J

2.6

Figure 5.13 Effect of carbonation time

I 6 % . 4 %

J , 39

MOR(MPa) Flexural Mass Gain(%) CaC03 Depth Modulus(GPa) (x100%)

Batch Bl

Batch B12

Batch B17

Figure 5.14 Cross section ofBl, B12 and B17

69

Page 82: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

CD

C 3

0

4.6

S5Bar(B1) H4Bar(B10) 0 2Bar(B11)

2.4 2.4

C02 time=15min Concentration=100%

One supply

0.62 0.52 0.39

MOR(MPa) Flexural Modulus(GPa)

Mass Gain(%) CaC03 Depth (x100%)

Figure 5.15 Effect of carbonation pressure

Batch BIO

Batch Bll

Figure 5.16 Cross section of BIO and Bll

7 0 -

Page 83: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

7

6

5 CD T3

c 4 O) CD

3

2

1

0

£3 Thickness=12.7mm,cement (B1) E3Thickness=6.4mm,cement (B14) EThickness=12.2mm,slag (B4) E\ Thickness=6.4mm,slag (B15)

C02 time=15min Pressure=5bar

Concentration=100% One supply

54

4 6

4 2

wwm.

1 t

2.1

:-:-: 1.2

4.7

24

38

3 1

1 4 11

4 7 46

1.0 1.0 1.0 0.62T

MOR(MPa) Flexural Modulus(GPa)

Mass Gain(%) CaC03 Depth (x100%)

Figure 5.17 Effect of specimen thickness

Batch Bl

Batch B14

Figure 5.18 Cross section ofBl and B14

71

Page 84: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

8

7

6

0) 5 -•o 3

I 4 03

3

2 H

1

0

C02 time=15min Pressure=5bar Concentration= 100% One supply

4.6

2.6

2.1 2.4 2.4

1-4 1.3

^Cement (B1) ^ Fiber cement (B6) BSlag (B4) EH Fiber slag (B7)

38

4.7 4.7 4.9

II 0.62 0 - 7

1.0 1.0

iH s :-:-:-:;

MOR(MPa) Flexural Mass Gain(%) CaC03 Depth Modulus(GPa) (x100%)

Figure 5.19 Effect of cellulose fibers

72-

Page 85: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

6

5

4 CD

•o +-.

c 3 CD

2 ^

4.6

S Cement (B1) • Slag (B4)

P2 Ground waste cement (B18)

3.8

2.4 2.1

1.3 1.4 T l 1 . 1

C02 time=15min Pressure=5bar

4.7 Concentration^ 00% One supply

2.5

H

1.0

0.62 0.35

MOR(MPa) Flexural Mass Gain(%) CaC03 Depth Modulus(GPa) (x100%)

Figure 5.20 Effect of binder

Batch Bl

5tf/c/z 54

Batch Bl8

Figure 5.21 Cross section ofB21, B4 and B18

73

Page 86: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

l^"**" ".?

• Batch B4

Batch Bl

Figure 5.22 SEM of batch B4 and Bl

74-

Page 87: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

CD "a _3

' c en

10

9

8

7 H

6

5 H

4

3

2

1

0

• 0 El

15 min, one supply (B1) 120 min, one supply (B17) 120 min, continuous supply (B21) 180 min, continuous supply (B22)

6.5 6.5K:-:

7.2

Concentrat ion^ 00% Pressure=5bar

7 6

4.6 4 9

I 4 7

4.0 vl

2.4

K l 2 0

J i

3 8

0.62f

111

1.0 1.0 1.0

MOR(MPa) Flexural Mass Gain(%) CaC03 Depth Modulus(GPa) (x100%)

Figure 5.23 Carbonation at 100% CO2 concentration

Batch Bl 7

Batch B21

,

mm.

Batch B22

Figure 5.24 Cross section ofB17, B21 and B22

75-

Page 88: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

CD o

E 03

Concentration=25% Pressure=5bar

35

^ 15 min, one supply (B9) S120 min, one supply (B16) B 120 min, continuous supply (B20)

1.7

2 9

1.0 0.7

,.

2.7

0.8

_d

1.2

0.12, 0.25 0.34

MOR(MPa) Flexural Mass Gain(%) CaC03 Depth Modulus(GPa) (x100%)

Figure 5.25 Carbonation at 25% CO2 concentration

Batch B9

T%ifr :;—,•*$>

ferff ..rf*? " UML."J> •*£**** tor*** •**> Vwtwemf

Batch B16

Batch B20

Figure 5.26 Cross section ofB9, B16 and B20

76.

Page 89: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Cement, dry C02(B21) I Cement, moist C02 (B24) I Mortar.dry C02 (B26) I Ground waste cement, dry CQ2 (B23) 79

Concentration^ 00% Pressure=5bar Time:r2 hours

Continuous supply 7 2

7 4

: • -

1 ! 3.2

1.0 1.0 1.0

0 4 5

MOR(MPa) Flexural Modulus(GPa)

Mass Gain(%) CaC03 Depth (x100%)

Figure 5.27 Carbonation at continuous CO2 supply of two hours

-71-

Page 90: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

CD

3

c 4 o>

0 120min continuous supply paste(B21)

S3 7days air curing paste (B25)

0 120min continuous supply mortar,dry

C02 (B26) (3 7days mortar Air curing (B27)

MOR(MPa) Flexural Modulus(GPa)

Figure 5.28 Comparison of 2 -hours carbonation curing with 7-day air curing

Batch B26

Batch B27

Figure 5.29 Cross section of Mortar B26 and B27

78

Page 91: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

60

50

CD •o 3

40

30

20

10

57 1

H I 53.e IB1 SB17 DB20 0B21 E3B26

Compressive strength air curing:

Paste(B25): 46.4 MPa Mortar(B27): 44.6 MPa

29 5

5 51 6 5, 1

Compressive Strength (MPa) right after

carbonation

Compressive strength (MPa) after 2 months

Figure 5.30 Compressive strength of carbonated concrete plates

79-

Page 92: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Chapter 6

Conclusions

Feasibility of carbon dioxide uptake by concrete products through early age curing

was studied. The process parameters examined included the CO2 concentration, the

carbonation time, the carbonation pressure, the type of binder, the chemical additive, the

thickness of the specimen, and the CO2 supply method. The performance of the

carbonated products was evaluated through the measurement of pressure drop,

temperature rise, strength development, mass gain and carbonation depth. The following

conclusions can be drawn:

(1) It is possible to carbonate the CaO-based cementitious materials in two hours

or less to fast produce concrete building products with sufficient strength and certain

amount of CO2 uptake. In general, higher CO2 concentration, longer carbonation time,

higher CO2 pressure can produce stronger products and promote more CO2 absorption.

(2) The best results obtained from this preliminary study are the Portland cement-

based concrete products carbonated two hours under 5 bar pressure with 100% CO2

concentration using continuous CO2 supply method. The two-hour compressive strengths

exceeded 40 MPa and the two-hour moduli of rupture (MOR) were over 6 MPa, both of

which satisfied the minimum requirement for concrete block and cement board

applications. The corresponding CO2 uptake by the concrete reached 7-8%. For 12.7 mm

thick plate samples, the carbonation went through the entire thickness in two hours.

(3) The manufactured C02 gas was used in this study. The 100% C02 was

employed to simulate the recovered CO2 from the exhaust gas, and the diluted CO2 at

-80-

Page 93: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

25% and 50% concentration was to mimic the as-captured or partially recovered CO2.

Although the low CO2 concentration generated low strength gain and low mass gain, the

strength developed using 25% C02 in two-hour carbonation still satisfied the minimum

requirement for block application. Moreover, the partially carbonated concrete obtained

the full strength after left in the air two months for further curing. However, the C02

uptake was low with 25% concentration. A longer carbonation time (more than two hours)

or higher pressure (higher than 5 bar) would be a solution to improve the CO2 absorption,

if the concentration of the gas could not be enhanced in an economical way.

(4) The continuous CO2 supply method proved to be technically effective and

practically feasible in full scale concrete production using carbonation curing. The

continuous CO2 supply in carbonation process compensated the CO2 diminishing

automatically and promoted the CO2 absorption by concrete to the maximum. For the

full-scale real production, it is suggested that the carbon dioxide gas be injected into the

chamber first in a continuous supply manner at a given pressure and to a required time,

and then the valve be turned off to switch to one-time supply for concrete to consume all

the remaining CO2 gas before opening the chamber. The pressure drop in one-time supply

can be used to monitor the CO2 starvation and the strength gain. The carbonation time and

pressure can be calculated and programmed to make the process itself clean.

(5) Non-uniform carbonation along the thickness was a concern in the early

studies and had hindered the commercial applications of the technique. It was shown in

this research that if the carbonation time was allowed to be extended to more than two

hours, it was highly possible to achieve all solid along a 12.7 mm (0.5 inch) thickness. It

is a perfect geometry for cement board. However for concrete products with thicker

members, it is a challenge to obtain full carbonation. More studies are necessary to find

-81 -

Page 94: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

the optimal combination of a variety of process parameters for total carbonation. If total

carbonation is not possible for thick members, it is interesting to know the performance of

a concrete with the skin made of carbonates and the core made of hydrates.

(6) The so called "full carbonation" in this study because of the all-solid hardness

developed along the entire 12.7 mm thickness did not mean the total carbonation. This

was confirmed by phenolphthalein solution treatment. A large number of red spots were

observed on the cross section although the hardness was proved by scratch using the steel

pen. The low mass gain was another evidence. If total carbonation is achieved, the mass

gain due to the CO2 uptake should reach approximately to 50% by weight of binder. The

highest mass gain obtained in this study was only about 8%.

(7) The mass gain calculated in this study was not accurate. The true C02 uptake

could be higher because the water evaporation during carbonation was significant and

was not considered in the calculation.

(8) Portland cement seemed to be the best binder for CO2 absorption for both mass

gain and strength development. Ladle slag and ground waste cement were not good for

strength, but absorbed certain amount of the carbon dioxide gas. A hybrid system to blend

cement with slag or waste cement would be efficient for carbonated concrete products to

consume more CO2 and maintain at least the same strength.

(9) The chemical additives did not make the same contribution to the bending

strength as it did to the compressive strength. For high content of CaO, fast reaction did

not produce more solid carbonates. Instead, the considerable heat generated resulted in a

delamination failure in plate specimens.

(10) Cellulose fibers did not significantly improve the C02 absorption. This

phenomenon is worthwhile a further study since other studies pointed out the cellulose

- 8 2 -

Page 95: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

could be a good C02 absorbent. Cellulose fibers are commonly used in cement fiberboard

production with a large percentage for strength and toughness. The surface treatment of

the fibers is economically feasible and could be tailored to the CO2 uptake.

(11) Porosity is an important parameter for carbonation. Mortar mix with sand

was more porous than the paste mix. The mortar mix developed similar strength as paste

mix but gained a higher percentage of CO2 uptake. It demonstrated the carbonation

process could be an ideal curing method for concrete block production because of its

porous nature of the product. Compared to the currently used steam curing, carbonation

dose not require pre-setting period and thus can shorten the curing time substantially.

(12) The presence of water in carbonation is critical. The moist CO2 could be

another approach to improve the carbonation efficiency and requires a further

investigation.

- 8 3 .

Page 96: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

References:

Bukowski, J.M. and Berger R.L. (1979), "Reactivity and Strength Development of

Activated Non-Hydraulic Calcium Silicates", Cement and Concrete Research. Vol.9,

pp57-68.

Halmann, M.M. and Steinberg, M. (1999) "Greenhouse Gas Carbon Dioxide Mitigation * ,

Lewis Publishers, CRC Pressed, NY, pp5-19.

Hermawan, D. and Hata, T, (1998), "Development Technology of Rapid Production of

High-Strength Cement-Bonded Particleboard by Using Gaseous or Supercritical Carbon

Dioxide Curing", Proceedings of inorganic-Bonded Wood and Fiber Composite

Materials, Vol.7 pp70-87.

Mourits, F. (2001), "Capture and sequestration of greenhouse gases in Canada", Natural

Resources Canada Annu. Rev. Energy Environ, ppl-13.

RILEM (1988), "edition CPC 18 Measurement of haiurdened concrete carbonation

depth" Technical Recommendations for the Testing and Use of Construction Materials

1994,pp453-455.

Simatupang, M.H. and Habighorst, C. (1995), Invextigations on the Influence of the

Addition of Carbon Dioxide on the Production and Properties of Rapidly Set Wood-

Cement Composites, Cement & Concrete Composites, 17, pp 187-197.

Teramura, S. and Isu, N. (Nov.2000), "New Building Material from Waste Concrete by

Carbonation", Journal of Materials in Civil Engineering, pp288-293.

Wagh, A.S., Singh, D., and Knox, L.Jr (April 1995), "Lab studying Greenhouse Effect on

Concrete Setting", Concrete International, pp41-42.

• 8 4 -

Page 97: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

Worrel, E., Price, L., Martin, N (2001), "Carbon Dioxide Emissions from the Global

Cement Industry", Annu. Rev. Energy Environ. 26, pp 303-329.

Young, J.F., Berger, R.L. and Breese, J. (1974) "Accelerated Curing of Compacted

Calcium Silicate Mortars on Exposure to C02" Journal of The American Ceramic Society,

Vol.57, No.9. pp394-397.

85

Page 98: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

CO

m m ii 0) & _ CO CO CD l _ Q .

CM

O o

i n

-<-> w <L»

H

der

a

>» U >-£ C/l <U

CS H «< X

-a a <u

a a

I I CM

o O

CO 0 . 2 CO II c o

cti

mpa

o "—-. fc F

^ t i n CM II

. c

E b

CM

IL

a> • D _C

>> o

I

o en 2 +

_CD

"co

<: +, "c CD

E CD

o -3-O

I o CO

Z + i —

CD +-. CD

nt+W

CD

E CD

O

CO O

I

er+N

aOl

men

t+W

at

CD

o CM

o

1 _

CD

15 + q o

Bat

ch

CO

4 o

CM

4 o

i

3

CO 1

CO O

CM

CO O

T —

I CO O

CO

CM o

CM 1

CM O

i

CM O

CO

T— o

CM •

CJ

• < -

^-o

c CD

E o <D Q .

2 CO

3

o o i n

o o i n

o o m

o d m

o d i n

o d i n

o d i n

o d i n

o d m

o d i n

o d i n

o d m

CO

c CD

E CD

J

o o

o o

o d

o d

o d

o d

o d

p d

o d

o d T—

o d

O

d T_

CD

15

OC

0 0

T -

oo

T—

• > -

• > -

T—

1 -

d

T -

d

T -

d

Z

3 CM

CO D CO

J

5 C O CO

/) s 3<

• CM CD 0 0 O CD •**• •tf CO p j CD CM — CO ^ ^ O 1 - ° °

i n i r i 1~

:M T - i n o t o s 3> T - • CD CM ^ :

"*" d CO

0 0 0 0 CD CM CD CD CM co ~ CM CM - : n i n " I D T - ^ i n i n

. c c I

t

c I

c c u

CJ r-c Cl

c c it

0 a T"

I f

IT

• ^

C

cc

a oc I T

5 CO i—

W -—• • — "tii

J c g o w

• co - Q co

<t ^ t O O CD N c i n _-: •>- CM • D 0 0 r l CM T - ^ ri i n

^ i n u) K co i n J 9 n ® ^ r-'

n 1 - c o

- 0 0 -<s- i— CD o o T - _ j i n C M ~ ; D 0 0 ^ CM T - ^

o i n

O O ) S v CD ^ f " CO fv i N CM •

5 d

M N S CO CD CM

»• fe CM £ 2 ^ CD CM CO

•r1 CM

•J co i n o co T -3 £ - ,_: Tj- CM • - CM - i - x - ^

i d

) i - f 0 0 CD CM r CM • ^ CM •

o i n T -

1- CD i - 0 0 CO CO 5 ^ T- ' tr> <N ^ 5 CO ^ T—

T ^ • r ! co ^ co co > CO r - ^ ^

> co -<t CD co i n > O p j 0 0 CM ,_•

i d ^ T~

"co" 'ro~ a. CL 2 2

^ ^ £1 JZ

2 - "Si "So "O 0 CD CO ^- i -)v +_, +_,

•> ° in in CO ^ p C C C ^ o

• ^ ^ O .—. O O o -

Mas

s af

ter

Mas

s ga

in,

Com

pres

si

Are

a (m

m2

Com

pres

si

Com

pres

si

Mas

s ga

in,

Com

men

t

Page 99: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

CO CD in II CD

co co CD

CM O O

E in

II CM O O co" 0 .

00 II c o

V-'

o CO CD. E o o

'E

E

iri CM II E E

CM

CD TO

g ">* O

I o CO

z

g+W

+

CO

CO oo O

NaO

H

+ 5 £ H CD

E CD O

CD

1o CO

5 O

NaO

H

+ CD

nt+W

a

CD

E CD

O CD

o

5 + X o CO

z + c CD

Cem

i n O

c "ct

m

CO

CO

O

CM i

00

O

,_ i

00

O

CO

O

CM i

r O

o

CO •

CD

o

CM i

CD O

1

CD O

CO

ID

O

CM

i n O

t

i n O

c CD

E o CD Q CO

3 15 Q

o d i n

o d i n

o d i n

p d

o d i n

o d i n

~5 c CD

E CD

O

i n

i-^

i n

i n

Ni

m r

i n

h-i

i n

r--'

i n

r-

i n

i-^

i n

r-

o d

o d

p d

_c \_ CD

CM

• ^

CM

CM T_

CNj

CM

'-'

CM T —

CM

^

CM

CM

i n

CM

i n

CM

m CM

~5 X O Is

2 CM

X

g "co O

O CO

O

o m

o i n

o i n

"S ~5 CO

CO CD

" O

CO _ l

o i n

o i n

o i n

c CD

g O

CD -»—1

CO CO

5

2 TO

CO CO

CD JD LL

, o 2

r— O CD

4

o iri

i n CO CD

iri

r OO

4

CD N -CD

4

CD oo r^ 4

o CM

in

CM

i n iri

r i n iri

CM OO CM

i n

r

i n d

S CD

ID n CO CO

CO

2

CM

iri

CD CO CM

iri

CD CD 00

iri

CO CM

iri

oo T —

iri

i n CD

iri

i~-0 0

iri

CO

o 00

iri

CO CO 0 0

iri

CD CO

i ^

CD

r-d

1o CO CO

CO

2

0 0

4

C D

4

I - -

4

CO

CD

"* CD

i n

0 0

i n

iri

h -

4

CM

iri

CO

CM

O

O0

CO

C

CO

c j CO CO

CO

2

r CD

00 T—

o

CO 1^-CD

i n CM i n

T j -

o CM

CO

co

CM CO o

CD

o 00

l*~

CD

°°. 5 m

r CD i n

CN

d CM i n

z "O CO

o c o 10 CO

a E o O

CD CM

CD CM

CO CM

CD CM

CO CM

CO CM

CO CM

CO CM

CD CM

CD CM

CO CM

CD CM

E _E CO CD

<

CM

r-

p 00

h -

s!

4

i n

d

CO

iri

CM

0 0

^ d

0 0

r

CO

4

i n

4

CM

4

"co" D. 2 .c CX C CD

CO c o CO CO CD i _

a E o O

r

CO

d

i n

N-'

co 4

"to" 0. 2 .c "co c CD

c/5 c o to co CD k_

a E o O

0 0

*— d

,-iri

o CO

S? c CO

cr <o CO CO

2

1 E o O

r— oo

Page 100: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

(

(

(

>=15

min

; C

02

pre

ssur

e=5

Bar

3 M

Pa;

C02

mpa

ctio

n=

.4m

m),

Co

Cyl

inde

r (r

=12.7

mm

h=

25

I Bat

ch X o ^ CO c \ Z I CD

ne

nt+

Wa

I

c12

-2

CD

O T •M ™

5 ° r D co co J-2 ,-

+ —

j^e

me

nt+

u

I C

11-2

o i i

was

is

C11

-1

ii-T

iTiy

ds

n

C6-

3 C

10-2

C

10-1

C

9-3

C9-

2 C

9-1

Spe

cim

en

50.0

7.

5 1.

2

5.32

7 5.

704

7.1

1428

126

11.3

50.0

7.

5 1.

2

5.38

5

5.75

3 6.

8 15

20

126

12.1

11

.7

6.9

30m

in

O i n . . co co n

S s - ^ °°. co 5 ™ ^ m m *- 'r"

35.0

7.

5 1.

2

15

5.55

2 5.

899

6.3

1618

126

12.8

S - - - P ^ d S ^ d d c o

35.0

7.

5 1.

2

15

5.03

5 5.

382

6.9

1084

12

6 8.

6

O . A H . •*- CD ,n *>. ™. m C M i n c D c o c o c M

8 ^ - - ° ° q ^ g ^ i r i T m

o , « „ . CD 00 O h-

CO ' - *T T * *— CO •<r m ^

o CM m S ^ ^ m ^ - c D r - . C M < O c o i£ r-- •<- •<- r~ CD ^ : CM CM • CO • ^ Tj- •»— CO

1 1 5 SR3S8S m m *- , -

m m •<- ^ ^

50.0

10

.0

1.8

5.09

4 5.

311

4.3

2209

12

6 17

.4

uate

C

emen

t (g

) W

ater

(g)

NaO

H (

g)

Ca(0

H)2

(g)

CaO

(g)

Ladl

e S

lag(

g)

Wa

ste

cem

ent (g

) F

lash

Ash

(g)

San

d (g

) F

iber

(g)

MC

(g)

Mas

s be

fore

(g

) M

ass

afte

r (g)

Mas

s ga

in,%

C

ompr

essi

on l

oad

(N)

Are

a (m

m2)

Com

pres

sion

Str

enqt

h(M

F

Com

pres

sion

Str

en

qth

fMF

M

ass

gain

,%

Com

men

t

oo oo

Page 101: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

o 00

CD

m m II 0 i _ 3 CO CO

0

CN o o c£

E in

IT CN o o CD* 0_

CO II c o o CD Q. E o O

If E

i n CN n

E E i ^ CM

0 TD _C

">> (J

<: + X o CD Z

em

en

t+

o • *

o

X

o CO

Z +

ter

t+W

a

0 E 0 O co

O

Bat

ch

co •

"3-

O

C14

-2

4-1

O

3-3

O

3-2

T—

o

_ 1 CO

O

c 0

Speci

m

Dat

e

50 0

50

.0

50.0

CD o in

p o in

o o m

.—. DO

Cem

en

m s.

7.5

in h~"

in h-'

in

r

in r -'

"oo

Wa

ter

(

CN

• * -

1.2

CN

CM T~

CN ,-i

CM <c—

s X

o CO

Z

S Si X o CD

3 O CO

O

s ~oo CO CO 0

3

DO

CO

G.

Gla

s DO •D

c CD

CO

DO

ll

CO 4

.8

5.23

1

CM 1^

5.4

CD CD

5.4

in m CM in

T —

5.4

DO

0 1

Mas

s be

foi

CM

4.8

5.

209

co

5.4

CD

5.9

00 co o CO

CN CN

5.9

-2

ter

Mas

s af

CD o •

-0.4

m CD

CO

CD • * '

,_

J" oo

-•s

Mas

s gain

,

in in CM

975

CN

CO

OO CN 00

oo 00 CO

2938

,—, Z^

T3 CO .o c o

SS

I C

om

pre

CD CM

126

CD CN

CD CN

CD CN

CD CN

^^

E

Are

a (

m

OO OO

7.7

Ti­ed

o CO CM

CO CD CO

CN CO CN

"co" a. ^ sz

ngt

0 i_

CO c o

SS

I C

om

pre

8.0

CO CD CN

"co" a. ^ x: DO C 0 i_

CO c o

SS

I C

om

pre

-0.5

CM T— T_

•5 c"

Mas

s ga

L_

'<

4hou

rs

CM

c E o CM

c 0

E 1

Page 102: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

E E

CO

II c CD CL CO i

CO CL co

O II o

CO JO m II CD i_ •3 in 10 CD i_

CO-

CM

O o

+* «3 <U H <u

C-s-£

les

A « H ca X

TS S3 OJ

a. <C

11 CM

O O CO LL 2 0 0 11 c

tio

0

a. E 0 0 -

E b

h -CM T -

X

CM , _ X

CM

CD I - -

(0 ao to CL

B4:

Sla

g(la

dle)

+W

B

3:C

+W

+C

a(O

H)2

B

2: C

+W+N

aOH

B

1:C

+W

(re

fere

nce)

I B

atch

B

4-3

j B

4-2

B4-

1 B

3-3

B3-

2 B

3-1

B2-

3 B

2-2

B2-

1 B

1-3

B1-

2 B

1-1

ISpe

cim

en

iDat

e 22

4 22

4 22

4 24

0 24

0 24

0 24

0 24

0 24

0 IC

emen

t (g

)

CO CO

CD CO

CD CO

CO CO

CO CO

CO CO

CO co

CD CO

CD CO

CD CO

CD CO

CO CO

IWat

er (

g)

5.8

5.8

5.8

|NaO

H (

g)

CD

CD

91-

|Ca(

OH

)2 (

g)

ICaO

(g)

24

0 |

240

240

|Lad

le S

lag(

g)

IG.

Gla

ss (

g)

ISan

d (g

) |F

ibe

r(g

) 25

7.5

| 25

7.6

257.

8 26

3.8

263.

4 26

4.2

263.

4 26

4.1

263.

8 25

8.1

258.

9 25

8.4

|Mas

s be

fore

(g)

26

8.2

| 26

8.1

268.

3 27

4.7

274.

3 27

5.8

271.

8 27

2.7

271.

7 26

6.7

267.

3 26

7.3

|Mas

s af

ter

(g)

4.8

| 4.

7 4.

7 4.

8 4.

8 5.

0 3.

7 3.

7 3.

4 3.

8 3.

7 4.

0 |M

ass

gain

,%

135

| 16

9 15

8 26

2 20

6 16

9 27

6 22

3.9

225.

9

260

422

438

|3P

B lo

ad (

N)

12.2

|

12.2

12

.2

13.5

13

.5

13.7

12

.7

12.7

12

.6

12.6

12

.8

12.7

T

hich

ness

(m

m)

0 0

2.3

2.1

2.9

2.3

0 0

3.4

2.8

2.8

3.3

5.2

5.4

|MO

R(M

Pa

)

All

solid

4.

5 4.

5 4.

9

CO

2.9

CO

3.8

• *

• *

? E CO CO CD

c 0

j= ( -CM O O

1 a 0 H

3.9

3.5

3.8

2.1

2.1

2.2

3.7

• *

• < *

|Bot-

C02

Thi

chne

ss(m

m)

1.3

| 1.

5 |

1.4

|

0 0

1.2

0.7

2.5

2.2

2.2

00

3.0

2.6

|E(G

Pa)

m

1 0

m

1 0

Pre

ssur

e(B

ar)

Om

in

CO

3.3

3.6

3.3

Pre

ssur

e(B

ar)

5min

2.

2 |

2.5

3.1

2.7

Pre

ssur

e(B

ar)

10m

in

1.9

I 1.

9 2.

8 2.

2 P

ress

ure(

Bar

) 15

min

2.

1 I

2.3

3.0

4.6

|MO

R(M

Pa)

1.

4 I

1.2

2.3

2.4

Fle

xura

l M

odul

us(G

Pa)

4.

7 I

4.9

3.6

3.8

|Mas

s G

ain(

%)

12.2

8.

4 5.

1 7.

8

J =

Q. CD

Q CO

0 0 CO

O

CH

/C=

7%

Com

men

t

o ON

Page 103: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

E E

CO

II c CO CO­CO I

CO CL CO

o II o

5 £ CD

CO m II CD l _

CO CO CD h _

CL CM O o E m IT CM O O co"

0 .

00 II c o "o CO Q . E o o

1" E

CM

CM

X

CM

CO

r ^ CO

ao JO

CL

B8:

C+

CaO

B

7:

Sla

g+w

ater

+fib

er

B6:

C+

W+

1.9%

(wt)

fiber

B

5:C

+W

5

0%

Co

2

iBat

ch

B8-

3 |

B8-

2 B

8-1

B7-

3 B

7-2

B7-

1 B

6-3

CM CO CO

CD CO

B5-

3 B

5-2

B5-

1 IS

peci

men

iD

ate

237.

2 |

237.

2 23

7.2

220.

8 22

0.8

220.

8 24

0 24

0 24

0 IC

emen

t (g

)

CD CO

CO CO

CD CO

CO CO

CO CO

CO CO

CO CO

CO CO

CO CO

CO CO

CD CO

CD CO

IWat

er(g

) |N

aOH

(g)

3 CJM.

o o

2.8

| 2.

8 2.

8 IC

aO (

g)

220.

8 22

0.8

220.

8 lL

adle

Sla

g(q)

|G

. G

lass

(g)

IS

and

(g)

4.3

4.3

4.3

4.3

4.3

4,3

__

ICel

lulo

se F

iber

(g)

|M

C(g

) 25

8.8

| 25

8.5

259.

9 23

9.1

238.

7 23

8.6

235

234.

6 23

4.4

264.

2 26

3 26

4.2

|Mas

s be

fore

(g)

26

6.2

| 26

6.2

267.

3 24

9.7

248.

5 24

8.9

244.

8 24

4.2

244

266.

8 26

6.6

267

[Mas

s af

ter

(g)

3.3

| 3.

4 3.

3 5.

1 4.

7 5.

0 4.

8 4.

7 4.

7

-

1.6

1.2

Mas

s ga

in,%

19

1 |

165

246

189

171.

5 15

9.6

321.

7 38

9 24

9.8

126

140

137.

5 J3

PB l

oad

(N)

12.9

|

12.8

12

.8

11.7

11

.5

11.3

12

.2

12.2

12

.2

co

CO

co

Thi

chne

ss (

mm

) 2.

3 |

2.0

3.0

2.8

2.6

2.5

4.3

5.2

3.4

1.5

1.7

1.6

MO

R(M

Pa

) 4.

5 |

4.5

4.8

CO

2.8

3.3

All

solid

m

m

m

CM

CM

2.1

To

p-C

02

Thi

ckne

ss(m

m)

3.8

3.7

3.1

-

-j

-

Bo

t-C

02

Thi

chne

ss(m

m)

1.9

| 2.

1 2.

2 1.

4 |

1.3

| 1.

8 2.

5 1.

6 3.

1 1.

2 1.

2 1.

2 E

(GP

a)

m

IO

m

m

Pre

ssur

e(B

ar)

Om

in

3.9

I

CO

CO

4.3

Pre

ssur

e(B

ar)

5min

3.

4 I

2.2

2.4

t-

Pre

ssur

e(B

ar)

10m

in

CO

CM

1.9

3.8

Pre

ssur

e(B

ar)

15m

in

2.4

I 2.

6 4.

3 1.

6 M

OR

(MP

a)

2.1

I 1.

3 2.

4 1.

2 F

lexu

ral

Mod

ulus

(GP

a)

3.3

I 4.

9 4.

7 1.

3 M

ass

Gai

n(%

)

7.6

11.6

8.

5 3.

1

sz. Q. CD Q

o O co O C

omm

ent

Page 104: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

E E

CD

c CD Q . in i

CD o_ CO

in CD II O

CO CD

in

D C/0 CO CD

CL

CM

O O

E in

II CM O O co

0_

00 II c _o "o CO Q .

E o o

E~ E

CM

x

CM

X CM CD

c/o ao

j o CL

B1

2:C

+W

B

11:C

+W

B

10

:C+

W

B9

:C+

W

25

%C

o2

IB

atc

h

B1

2-3

B

12

-2

B12-1

B

11-3

B

11-2

B

11-1

B

10-3

B

10-2

B

10-1

B

9-3

B

9-2

B

9-1

IS

peci

men

I

Date

240

|

24

0

240

240

240

240

240

24

0

240

24

0

240

24

0

ICem

ent

(g)

CD CO

CD CO

CD CO

CD CO

CO CO

CO CO

CD CO

CD CO

CO CO

CD CO

CD CO

CD CO

IWate

r (g

) |N

aO

H (

g)

|Ca(O

H)2

(g)

ICaO

(g)

Ladle

Sla

g(g

) |G

. G

lass

(g)

Sa

nd (

g)

Fib

er (

g)

MC

(g)

258.6

|

26

0.1

2

59

.5

260.2

259.2

26

0

259.3

260.2

2

59

.1

259.1

259.7

259.6

M

ass

be

fore

(g

) 266.5

|

268

267.2

265.8

264.8

264.9

267.5

267.8

266.3

26

1.1

261.7

261.3

|M

ass

aft

er

(g)

3.5

|

3.5

3.

4

2.5

2.5

2.2

3.

6

3.4

3.2

0.

9

0.9

0.8

M

ass

gain

,%

169

|

163

15

0

143

145

226

179

16

7

196

60.7

64.3

59.3

3P

B l

oa

d (

N)

12.8

|

12.8

12

.8

12.7

12

.6

12.6

12

.7

12.7

12

.7

12.6

12

.9

12.7

T

hic

hness

(m

m)

2.1

I 2.

0

CO

1.8

1.

8

2.8

2.

2

2.1

2.4

0.

8

0.8

0.7

M

OR

(MP

a)

3.5

|

3.4

3.5

CO

CO

2.9

3.2

4.

1

3.4

-

1.3

1.

2

To

p-C

02

Th

ickn

ess

(mm

) 2.8

|

2.9

2.6

CM

1.9

1.

9

2.7

3.2

3.

2

0.2

0.

3

0.3

B

ot-

C02

Th

ich

ne

ss(m

m)

1.6

|

1.5

1.

9

0.0

2.0

2.4

2.

3

2.2

2.

7

0.4

0.

9

0.6

E

(GP

a)

in

CM

• < *

in

|Pre

ssu

re(B

ar)

Om

in

3.2

|

0.8

2.4

4.4

|P

ress

ure

(Ba

r) 5

min

2.

6 I

0.2

1.

7

|Pre

ssu

re(B

ar)

10m

in

o

1.2

•-

Pre

ssu

re(B

ar)

15m

in

2.0

I 2.1

2.

2

0.8

M

OR

(MP

a)

1.7

2.2

2.4

0.7

F

lexu

ral

Modulu

s(G

Pa)

3.5

I 2.4

3.4

0.

8

(Mas

s G

ain

(%)

6.2

4.

9

6.6

1.

5

sz *-> a. CD

Q n o o CO

O

Ca

rbo

na

tion t

ime

(10m

in)

| P

ress

ure

(2bar)

P

ress

ure

(4

bar)

C

om

ment

CN OS

Page 105: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

E E

CD

O i i

II c CO CL C/0

CQ CL CO

o II o

CO CO in II 0 L_ D co CO 0 k _ CL

CM O o E in II

CM O O to"

CL

00 II c g o CO CL

E o o

E" E

CM

x i ^ CM

X

CM

CD

CO

£ jo CL

B16

:C+

W+

25%

C02

B

15:S

lag(

ladl

e)+W

B

14:C

+W

B

13:C

+W

IB

atch

B

16-3

|

B16

-2

B16

-1

B15

-3

B15

-2

B15

-1

B14

-3

B14

-2

B14

-1

B14

-3

B13

-2

B13

-1

Spe

cim

en

I D

ate

240.

01

240.

0 24

0.0

o

o

o

120

120

120

240

240

240

ICem

ent

(g)

36.0

36

.0

36.0

00

00

00

CO T—

00

81.

co CO

CO CO

CD CO

IWat

er (

g)

iNaO

H (

g)

|Ca(

0H)2

(g)

3 O CO

O

120

120

120

|Lad

le S

lag(

g)

|G.

Gla

ss (

g)

San

d (g

) Fi

ber

(g)

O 2

260.

1|

260.

1 26

0.1

129.

3 13

1.5

129.

3 12

9.5

129.

7 12

9.5

259.

2 26

0.1

258.

9 M

ass

befo

re (g

) 26

2.8|

26

2.5

262.

9 13

4.4

137.

1 13

4.1

135.

8 13

6 13

5 26

5 26

5.7

265.

2 M

ass

afte

r (g

) 1.

2

-

1.2

4.5

4.9

4.3

5.6

5.6

4.9

2.6

2.5

2.8

Mas

s ga

in,%

oo

204

121

27.6

18

.7

26.5

CM OO

r-

00 oo

242

213

184

3PB

loa

d (N

) 12

.7|

12.7

12

.7

6.4

6.3

6.1

6.5

6.4

6.4

12.7

12

.7

12.7

T

hich

ness

(m

m)

1.0

2.5

1.5

1.3

0.9

1.4

4.4

3.5

4.8

3.0

2.6

2.3

|M0R

(MP

a)

2.1

2.3

2.1

-

All

solid

A

ll so

lid

CO

2.8

3.2

Top

-C02

Thi

ckne

ss(m

m)

1.9

2.1

2.1

Bot

-C02

Thi

chne

ss(m

m)

0.94

57|

1.13

89

0.97

596

3.51

6937

2.

7521

65

1.77

1985

4.

6990

4 4.

6596

6 4.

9991

8 2.

1887

66

1.90

4882

1.

9485

56

|E(G

Pa)

in

in

in

in

Pre

ssur

e(B

ar)

Om

in

4.5

I 3.

6 3.

4 3.

2 P

ress

ure(

Bar

) 5m

in

4.4

| 3.

4

CO

Pre

ssur

e(B

ar)

10m

in

4.3

| 3.

2 2.

9 P

ress

ure(

Bar

) 15

min

3.

8 I

Pre

ssur

e(B

ar)

120m

in

1.7

I 1.

2 4.

2 2.

6 |M

0R(M

Pa)

1.

0 I

3.1

4.7

1.9

Fle

xura

l M

odul

us(G

Pa)

1.

2 |

4.6

5.4

2.6

Mas

s G

ain(

%)

3.2

6.3

6.4

5.0

sz -Q. 0 D CO o o CO

O

carb

onat

ion

time

(120

min

) ca

rbon

atio

n tim

e (5

min

) C

omm

ent

Page 106: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

E E

CD

II C CO C L CO I

CD CL CO

O

CJ

CO CD in n 0 L _

D CO CO 0

CM

O o E in n

CM O O

co" CL

00 II c .g to CO Q . E o o

E E

CM

CM

X

CM

CO

CO 0

JO CL

B20

: C

+W

+25

%C

02 C

onts

| B

19::C

+W+3

.5

Bar

Air

B18

:Was

tece

men

t+W

B

17: C

+W

IBat

ch

B20

-3 |

B

20-2

B

20-1

B

19-3

B

19-2

B

19-1

B

18-3

B

18-2

B

18-1

B

17-3

B

17-2

B

17-1

IS

peci

men

iD

ate

240

| 24

0 24

0 24

0.0

240.

0 24

0.0

240

240

240

ICem

ent (

g)

CD CO

CD CO

CD CO

36.0

36

.0

36.0

70

.8

70.8

70

.8

CO CO

CD CO

CO CO

IWat

er (

g)

|NaO

H (

g)

|Ca(

OH

)2 (

g)

iCaO

Jg)

lLad

le S

lag(

g)

240

240

240

|Was

te c

emen

t (g)

|S

and

(g)

iFib

er (

g)

IM C

(g)

259

| 25

9.3

258.

8 25

9.8

259.

9 25

9.7

212.

2 19

8.8

281

259.

3 25

9.6

259.

9 |M

ass

befo

re (

g)

265

| 26

5.5

264.

9 25

9 25

9.1

259

217.

2 20

2.6

285.

2 27

4.1

273.

7 27

5.1

| M

ass

afte

r (g

) 2.

7 2.

7 2.

7 -0

.4

-0.4

-0

.3

3.1

2.5

1.9

6.6

6.2

6.7

|Mas

s ga

in,%

17

6 |

296

380

CO

27.6

26

.1

128

in oo

147

413.

7 40

3.7

375

|3P

B lo

ad (

N)

12.7

|

12.7

12

.7

12.6

12

.7

12.7

12

.7

11.9

16

.2

12.7

12

.7

12.7

|T

hich

ness

(m

m)

2.2

| 3.

7 4.

7 0.

4 0.

3 0.

3 1.

6 1.

3 1.

1 5.

1 5.

0 4.

7 |M

OR

(MP

a)

2.9

| 3.

1

CO

o

o

o 2.

3

CM

2.5

1.1

|

*—

-

o

o

o 2.

2

CM

2.3

All

solid

|T

op-C

02 T

hick

ness

(mm

) |B

ot-C

02 T

hich

ness

(mm

) 2.

5 2.

3 2.

5 0.

5 0.

3 0.

4 1.

2 1.

3 0.

7 1.

9 2.

0 2.

0 |E

(MP

a)

in

3.5

in

in

|Pre

ssur

e(B

ar)

Om

in

in

3.5

4.4

3.6

|Pre

ssur

e(B

ar)

5min

in

3.5

4.1

CO

Pre

ssur

e(B

ar)

10m

in

in

3.5

3.9

2.4

|Pre

ssur

e(B

ar)

15m

in

in

3.5

0.2

Pre

ssur

e(B

ar)

120m

in

3.5

I 0.

4 1.

3 4.

9 |M

OR

(MP

a)

2.5

I 0.

4 -

2.0

iFle

xura

l M

odul

us(G

Pa)

2.

7 |

-0.3

2.

5 6.

5 |M

ass

Gai

n(%

)

4.1

0.0

4.4

12.7

sz "a. 0 Q CO o o CO

o

Com

men

t

ON

Page 107: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

E E

CD

II c to CO­CO

m CL C O

o II o

CO

CO m n 0 i _

CO CO 0

l _

CO-CM

O o E m ¥ C M

O O co"

CL

00 II c g o CO Q .

E o o

? E

i ~ -C M

1 ^ CM T -

X

CM

C O

£-_ co 0

•4—»

JO CL

B24

: C

+W

+co

nst

B

23

:Wa

ste

cem

ent+

100%

CO

2Con

ts

B22

:C+

W+

cont

s B

21:

cem

ent+

100%

CO

2 C

onts

IB

atc

h

B24

-3

B24

-2

B24

-1

B23

-3

B23

-2

B23

-1

B22

-3

B22

-2

B22

-1

B21

-3

B21

-2

B21

-1

ISpe

cim

en

| Dat

e 24

0 |

240

240

165

165

165

240.

0 24

0.0

240.

0 24

0 24

0 24

0 |C

emen

t (g

)

CD CO

CD CO

CO CO

O

m

o in

o m

36.0

36

.0

36.0

CD CO

CD CO

CO CO

|Wat

er (

g)

|NaO

H (

g)

|Ca(

OH

)2 (

g)

ICaO

(g)

|Lad

le S

lag(

g)

|G.

Gla

ss (

g)

ISan

d (g

) |F

ibe

r(g

)

DO

o 2

261.

4 |

259.

5 25

9.2

206.

9 20

6.8

205.

8 25

8.8

259.

7 25

8.5

258.

8 25

8.4

260.

1 |M

ass

befo

re (

g)

278.

4 |

275.

8 2

75

.8

212.

2 21

2.1

211.

5 27

5.3

277.

3 27

5.9

275.

5 27

3.5

277

|Mas

s af

ter

(g)

75

7.2

7.4

3.3

3.3

3.6

7.3

7.8

7.7

7.4

6.7

7.5

|Mas

s ga

in,%

52

2 35

9 34

4 13

8 14

5 12

4 49

8 52

9 54

9 46

9 59

1.9

596.

7 |3

PB

loa

d (N

) 12

.8 J

12

.6

12.7

12

.4

12.4

12

.4

12.6

12

.7

12.7

12

.7

12.7

12

.7

|Thi

chne

ss (

mm

) 6.

4 |

4.5

4.3

oq

1.9

1.6

6.3

6.6

6.8

5.8

7.3

7.4

|M0

R(M

Pa

)

All

solid

• *

3.9

3.8

1.7

1.8

1.7

All

solid

A

ll so

lid

|Top-C

02

Thi

ckne

ss(m

m)

|Bot-

C02

Thi

chne

ss(m

m)

3.4

| 3.

5 |

4.3

|

1.3

1.2

1.3

4.6

| 4.

6 |

5.0

3.8

| 4.

8 |

3.4

|E(M

Pa)

m

m

m

m

|Pre

ssu

re(B

ar)

0m

in

m

m

m

m

Pre

ssur

e(B

ar)

5min

m

m

m

i n

|Pre

ssur

e(B

ar)

10m

in

m

m

m

m

|Pre

ssur

e(B

ar)

15m

in

m

m

m

m

Pre

ssur

e(B

ar)

120m

in

m

|Pre

ssur

e(B

ar)

180m

in

5.1

I

oq

6.5

6.9

|MO

R(M

Pa)

3.

7 I

1.2

4.7

4.0

iFle

xura

l M

odul

us(G

Pa)

7.

4 I

3.4

7.6

7.2

|Mas

s G

ain(

%)

12.7

5.

6 12

.7

12.7

sz "5. 0 Q

CO

O o to O

CM

O o 0 t— zz

"in

o 2

Com

men

t

ir> OS

Page 108: CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURINGdigitool.library.mcgill.ca/thesisfile19587.pdf · CARBON DIOXIDE UPTAKE BY CONCRETE THROUGH EARLY-AGE CURING By Gang Ye Department

E E

CO

II c CO CO­CO

CD CL

co in CO

o

~5 LT CO

CD in n 0 i _ D co CO 0 L _

CO-

C M

O o E in II

CM O O CO*

00 II c g "o co o. E o o

E E

CM

X

h -CM

X

CM

CD

CO

£ CL

B27

: C

+W+s

and

+7da

ys A

ir B

26:

C+

W+

sand

Con

t S

B25

::C+W

+7da

ys A

ir IB

atch

B

27-3

B

27-2

B

27-1

B

26-3

B

26-2

B

26-1

B

25-3

B

25-2

B

25-1

IS

peci

men

D

ate

120

120

120

120

120

120

240.

0 24

0.0

240.

0 IC

emen

t (g

)

o CM

o CM

O CM

O CM

O CM

O CM

36.0

36

.0

36.0

IW

ater

(g)

|N

aOH

(g)

|C

a(0H

)2 (

g)

ICaO

(g)

Ladle

Sla

g(g)

|G

. G

lass

(g)

12

0 12

0 12

0 12

0 12

0 12

0 IS

and

(g)

iFib

er (

g)

3 O

253.

4 25

4.6

254.

7 25

5.1

255

254.

2 25

9.1

259.

7 25

9.1

|Mas

s be

fore

(g)

25

8.1

259.

1 25

9.6

264.

3 26

4 26

3.7

263

263.

9 26

3 |M

ass

afte

r (g

) 4.

0 3.

8 4.

2 7.

8 7.

6

00

1.7

1.9

1.7

Mas

s ga

in,%

51

0 48

1 41

8 44

2 36

3 55

7 29

0 40

7 36

0 |3

PB

load

(N

) 11

.9

CM

CM

12.1

5

CM

12.0

5 12

.7

12.7

12

.7

Thi

chne

ss (

mm

) 7.

2 6.

7 5.

8 6.

0 5.

0 7.

7 3.

6 5.

0 4.

5 |M

0R

(MP

a)

All

solid

T

op

-C0

2 T

hick

ness

(mm

) |B

ot-C

02 T

hich

ness

(mm

) 2.

9 2.

6 2.

1 2.

5 2.

1 2.

5 1.

6 2.

0 2.

1 |E

(MP

a)

in

|Pre

ssur

e(B

ar)

Om

in

in

|Pre

ssur

e(B

ar)

5min

in

|Pre

ssur

e(B

ar)

10m

in

en

|Pre

ssur

e(B

ar)

15m

in

in

|Pre

ssur

e(B

ar)

120m

in

6.6

6.2

4.4

|MO

R(M

Pa)

2.

5 2.

4 1.

9 |F

lexu

ral

Mod

ulus

(GP

a)

4.0

7.9

oq

|Mas

s G

ain(

%)

12.7

sz

"3. 0 Q CO o o CO

O

|Com

men

t

CS