Green Bricks Units using Different Cement Types and Recycled Aggregates

1, b, Anwar Mahmouda ,1Hanan Elnouhy

Housing and Building National Research Center,Cairo,Egypt1

anwarm79@yahoo.comb, hanan_elnouhy@yahoo.coma

Keywords: recycled aggregates, green bricks, cooling techniques, blended cements

ABSTRACT

The aim of this study is to produce innovative bricks using 100% "green" building materials. Normal

Portland cement CEM Ι 32,5N, Limestone Blended cement CEM ΙΙ B-L32,5, and Slag cement CEM ΙΙ

A-S32,5 were used. Two types of coarse aggregates were used: dolomite and concrete rubble as

recycled aggregates. Also, two types of fine aggregates were used: sand, and concrete rubble. The

manufactured bricks were tested at ages 3, 7, 14, and 28 days. After 28 days of curing, selected mixes

were exposed to elevated temperatures of 300°С and 600°С for 2 hours. Afterwards, they were

subjected to different cooling regimes. The cooling regimes were air cooling, water cooling (sprayed

every 5 minutes for 1 hour immediately after removal from oven), and quenching (immersed in water

for 15 minutes immediately after removal from oven). Tests were conducted according to both

Egyptian Standard Specifications (ESS) and American Society for Testing and Materials (ASTM) in

order to determine compressive strength, absorption percentage, and oven-dry weight. The results

showed that all tested mixes, including those subjected to the various cooling techniques satisfied the

conditions of load-bearing units and were also of normal weight according to both ESS and ASTM.

1-INTRODUCTION

Bricks are a widely used construction and building material around the world. Bricks are either

produced from clay with high temperature kiln firing or from Portland cement (OPC), consequently,

contain high embodied energy and have large carbon footprint. To reduce the use of OPC, the

incorporation of high-pozzolanic industrial by-product content for making concrete masonry blocks

becomes a preferred choice. A study investigated the effect of replacing (OPC) by 20% of basalt, as

natural pozzolana, on the physico-chemical properties of blended cement in comparison to silica fume,

granulated blast furnace slag, and limestone. The results showed that basalt has lower pozzolanic

activity at early ages than that of silica fume and slag, but increased at later age. It was concluded that

basalt has low pozzolanic activity and has a better filling effect on cement hydration with better

physico-mechanical properties than other pozzolanic materials. Extensive research has been conducted

on production of bricks from waste materials. However, the commercial production of bricks from

waste materials is still very limited. This is possibly due to potential contaminations from the waste

materials used, the absence of relevant standards, and the slow acceptance of waste materials-based

bricks by industry and public. For mass production of bricks from waste materials, further research is

needed on standardization, government policy and public education related to waste recycling and

sustainable development [1-3].

Using by-products and waste materials, such as ground granulated blast furnace slag(GGBS), cement

by-pass dust (BPD), run-of-station ash (ROSA), basic oxygen slag (BOS), plasterboard gypsum

(PG),incinerator bottom ash aggregate (IBAA), recycle crushed glass (RCG),recycled bricks (RB),

steel fibre (SF), and PVA-fibre for the production of environmentally friendly paving blocks was

investigated. The test results confirmed that a concrete paving mix containing 6.3%GGBS,0.7%BPD

and 7% OPC by weight can decrease Portland cement content by 30% in comparison to the percentage

currently being used in most factories, without having a substantial effect on the strength or durability

of the paving blocks produced in accordance to BSEN 1338:2003[4].

The behavior of high volume fly ash (HVFA) concrete blended with ground granulated blast furnace

slag (shortened as slag) under the effect of elevated temperatures was studied. Cement was partially

replaced by a Class F fly ash (FA) at a level of 70% to produce HVFA concrete (F70).F70 was

modified by partially replacing FA with slag at levels of 10% and 20% by weight. After curing, the

specimens were exposed to elevated temperatures. The incorporation of slag showed negative effect on

HVFA concrete before and after different heat treatments [5]. Sadek examined the effect of using air-

cooled slag (ACS) and water-cooled slag (WCS) in solid cement bricks. The behavior of the bricks was

evaluated at ambient temperature and after exposure to elevated temperatures. Mixes were prepared in

which sand was replaced either partially/fully by either ACS or WCS individually. Results indicated

the possibility of recycling ACS and WCS without processing as fine aggregates in bricks production.

The use of ACS resulted in a higher deterioration after exposure to elevated temperatures although it

increased the compressive strength of unheated specimens. On the other hand, the bricks which

contained WCS were thermally more stable than natural sand (NS) and ACS bricks [6].Also, another

research was conducted to investigate the behavior of both normal and high strengths concretes

subjected to elevated temperatures and subsequently to different cooling regimes [7].

An experimental investigation was conducted on the effect of thermal shock during cooling on residual

mechanical properties of fiber concrete exposed to elevated temperatures. Various cooling regimes

were used including natural cooling, spraying water for a series of durations from 5 to 60 minutes and

quenching in water. Results proved that the rapid cooling regimes such as quenching in water, or water

to concrete for 30 minutes or more, caused an action of "thermal shock" to concrete under elevated

temperatures. The experimental results indicated that, compared with natural cooling, thermal shock

induced by water quenching and spraying water caused more severe damage to concrete, in terms of

greater losses in compressive strength, splitting tensile strength, and fracture energy[8].

In this study, the effect of elevated temperatures and various cooling regimes on the properties of

aerated concrete was investigated. Air cooled materials were tested at room temperature and in hot

condition after exposure to fire. Water quenching effect was determined by testing the material in wet

condition right after the quenching and in dry condition at room temperature. Unstressed strength of the

material tested hot is relatively higher than air cooled unstressed residual strength up to 600°С. On the

other hand, water quenching decreased the percentage of the strength particularly when the material

was wet right after the quenching; strength was lost gradually as the temperature rose. As a result, if the

quenching effect is disregarded, temperature rise does not have a considerable effect on the strength of

the aerated concrete approximately up to 700 - 800°С [9].

In this study, the residual compressive strength of concrete with expanded perlite aggregate (EPA) and

pumice aggregate (PA) after it was exposed to elevated temperature and then cooled in three cooling

conditions (natural, water, and furnace cooling) was investigated. EPA and PA replacements of fine

aggregates were 10%, 20%, and 30%. Test results showed that the compressive strength of concrete

cooled in water cooling after being exposed to the effect of different mixtures with EPA and PA is

higher than that cooled in natural and furnace [10].

2-Materials and Methods

2.1 Cement

Portland cement CEM Ι 32,5N, Limestone Blended cement CEM ΙΙ B-L32,5N, and Slag cement CEM

ΙΙ A-S32,5N were used in accordance to ESS 4756-1/2009.Oxides percentages of cements are

presented in table1.

Table1:Oxide percentages of used cements

LSF: Lime Saturation Factor

2.2 Fine Aggregates (sand, and concrete rubble)

Siliceous sand and concrete rubble were used with 4.75 mm maximum particle size in this research

program. Table 2 gives the physical properties of fine aggregates.

Table 2: Physical properties of fine aggregates

Property Sand Concrete Rubble

Specific gravity 2.50 2.57

Volumetric weight (tons/m3) 1.61 1.68

CEM II/A-S 32.5

N

CEM II/BL 32,5

N

CEMI

32.5N

Type

21.89 17.64 21.04 SiO2

4.80 3.12 3.88 Al2O3

3.75 2.43 5.14 Fe2O3

60.08 60.01 63.21 CaO

2.74 1.49 0.97 MgO

2.86 2.93 2.45 SO3

3.21 11.95 2.72 L.O.I

0.38 0.22 0.43 Na2O

0.25 0.18 0.16 K2O

99.96 99.97 99.99 Total

0.72 0.71 0.52 Ins. Res

0.04 0.04 0.01 CƖ

0.55 0.35 0.53 Na2OEq.

0.84 1.07 0.92 LSF

6.38 4.16 1.60 C3A

2.3 Coarse Aggregates (crushed stone)

Dolomite and of 10 mm maximum particle size was used in this research. Table 3 shows the physical

properties of coarse aggregates.

Table 3: Coarse aggregate physical properties

Property Dolomite Concrete Rubble Acceptance limits

Specific gravity 2.55 2.61 −

Volumetric weight (tons/m3) 1.70 1.76 −

Absorption Percentage 1.5 1 Not more than 2.5% (1)

Clay and other fine materials

(%)

2 1 Not more than 3% by

weight (2)

Impact value (%) 26 18 Not more than 30% (2)

(1) According to the Egyptian Code of Practice issued 2007

(2) According to the Egyptian Standard Specifications 1109/2002

2.4 Mix proportions for solid cement bricks and methods

The control mix design for the manufactured product was selected from previous research work [11].

Six mixes were cast and tested at ages 3,7,14,and 28 days (except mix 6, which was tested at ages

3,7,and 28 days). Three types of cements were used. After casting, and until testing age, all specimens

were sprayed twice daily. Mixture proportions and testing matrix are given in table 4. Solid cement

bricks 26 x 12x 6 cm were manufactured by conventional equipment. Concrete rubble was used as

replacement for both coarse and fine aggregates. The manufacturing process involves compaction of

the mixed constituent materials in a mould followed immediately by extrusion of the pressed product

so that the mould can be used repeatedly. Since the finished product is required to be self-supporting

and able to withstand any movement and vibration from the moment they are extruded, very much

drier, higher fine aggregate content and leaner mixes are used than in the normal concrete work. The

demoulding ability is an essential criterion for manufacturing solid cement bricks. The water contents

of the solid cement bricks were adjusted based on this criterion. The (w/c) ratio was adjusted to

maintain an almost zero slump. It is worth mentioning that the high water content is imperative despite

of the dryness of the mixes due to the low cement content.

A series of tests were carried out according to ASTM C 67-03a [12] to determine compressive strength,

water absorption and Oven-Dry weight, values of the brick samples.

The brick samples were tested for compressive strength. The compression load was applied on the face

of the sample of dimensions 26 x12 cm. The compression strength was determined by dividing the

maximum load with the applied load area of the brick samples.

Water absorption and Oven-Dry weight values were obtained as follows: The samples were submerged

in water for 24 hours. Then, they were dried with a cloth to remove any water on their surface, and then

reweighed. The obtained weight was the wet weight of the sample. The samples were placed in the

oven at 105°С and dried to a constant mass and then taken out of the oven and weighed at room

temperature. The obtained weight was the dry weight of the sample. The water content of the samples

in both its wet and dry state was recorded. The Oven-Dry weights were calculated by dividing the

weight of the bricks (in the dry state) by their overall volume. Water absorption values were obtained

by dividing the weight difference in both the wet and dry state by the overall volume..

After curing for 28 days, the samples were exposed to 300, and 600°С in an electric oven. Then, the

furnace door was opened and the samples were allowed to cool. The temperature was maintained at the

respective temperature for 2 hours to achieve a thermally steady-state. Samples which were exposed to

300°С were cooled both naturally and by water cooling (sprayed every 5 minutes for 1 hour

immediately after removal from oven), while those which were exposed to 600°С, were also cooled by

the two previously mentioned regimes, in addition to, quenching(immersed in water for 15 minutes

immediately after removal from oven). Concerning specimens that were exposed to 600°С,

compressive strength was determined after applying the three cooling regimes, while absorption was

determined after exposure to air cooling and water cooling only. Mixture proportions and test matrix

are presented in table 4.

Table 4: Mixture proportions and test matrix

Constituents

Materials

(kg/m3)

Cement Fine aggregates Crushed Stone Water Slump

200 1000 1000 160-

170

Zero-1

Mix no. Cement types Aggregates Testing Cooling Regimes

after 28 days of

casting Coarse Fine Ages Temperatures

1(control)

CEM Ι 32,5N

Dolomite

Sand

3

7

14

28

R.T.

300°С

600°С

Air cooling

Water cooling

2 CEM ΙΙ B-L32,5N

600°С

Quenching

3 CEM ΙΙ A-S32,5N

4 CEM ΙΙ B-L32,5N Concrete

Rubble 5 CEM ΙΙ A-S32,5N

6

CEM ΙΙ B-L32,5N

Concrete Rubble

3

7

28

R.T.

--------

3- RESULTS AND DISCUSSIONS

Properties of bricks are herein presented using two approaches: the first one by considering the effect

of the different cement types, recycled aggregates, and elevated temperatures to which the specimens

were exposed to, while the second one by considering the effect of different cooling regimes. At ages

3,7,14, and 28.

3.1 Compressive strength

The compressive strength was tested at ages 3,7,14, and 28 days for mixes 1to 5. Mix 6 was tested at

ages 3, 7, and 28 days. All specimens were sprayed twice daily till testing age

It is worth mentioning that the method of testing in the ESS is the same as that in the ASTMC 67. The

ASTM states that only three specimens should be tested and did not mention the method of curing nor

at what age should the specimens be tested at [12].

Figure1 presents the effect of the three cement types on compressive strength at ages 3,7,14, and 28

days. Sand and dolomite were used as virgin materials in the three mixes. As expected, as age

increases, compressive strength increases. At all ages, CEM ΙΙ A-S32,5N (mix 3) provided the highest

strengths, while CEM Ι 32,5N (mix 1) yielded the lowest strengths. The limit of load-bearing units was

met at age 3 days for the three types of cements, indicating that it is feasible to use the produced bricks

after 3 days as load-bearing units (average compressive strength was greater than 13.1 MPa).

Regarding non-load bearing limit, it is suggested that cement content be reduced, as the compressive

strength was much higher than required (average compressive strength was higher than 4.14 MPa).

The effect of using recycled aggregates on compressive strength is shown in figure 2. Mixes 1,4, 5, and

6 satisfied the limit of load-bearing units at tested ages. These results indicate that it is possible to have

such bricks in the market at age 3 days. Mix 6 contained CEM ΙΙ B-L32,5N and fully recycled

aggregates in order to produce Green bricks.

As mentioned earlier, five mixes were exposed to 300°С and 600°С for 2 hours after 28 days of curing.

After exposure to 300°С, the specimens were cooled using two cooling regimes: air cooling, and water

cooling. Figure 3 presents the effect of the cooling regimes on compressive strength. The results

demonstrated that air cooling provided higher compressive strength than water cooling regarding the

five mixes. Again ,the mixes met the limit of load-bearing units regarding both Egyptian Standard

Specifications (ESS) and American Society for Testing and Materials (ASTM).

Specimens which were exposed to 600°С were cooled using three cooling conditions: air cooling,

water cooling, and quenching. Figure 4 shows the effect of the three cooling regimes on compressive

strength. The figure shows that, air cooling resulted in higher compressive strength regarding the five

mixes, as opposed to, quenching, which provided the lowest strength. These findings are in agreement

with previously research work [8].Yet again, the three cooling conditions satisfied the limit of load-

bearing units.

Table 5: Strength and Absorption Requirements [13-15]

Compressive strength,

min,(N/mm2)

Average net area

Water absorption, max, (Kg/m3) (Average of 3

Units)

Weight Classification-Oven-Dry Weight of

Concrete, (Kg/m3)

average of 3 Units Light weight Medium weight Normal weight

Loadbearing

units

Non-

loadbearing

Units

13.1 4.14 Less than 1680

288

(1680-2000)

240

2000 or more

208

Fig1: Effects of cement types on average compressive strength

Fig 2: Effects of cement types and recycled aggregates on average compressive strength

Fig 3: Effects of the two cooling regimes on average compressive strength after exposure to 300°С

Fig 4: Effects of the three cooling regimes on average compressive strength after exposure to 600°С

3.2 Oven-Dry weight and water absorption percentage

There are three classes of solid cement bricks: normal weight, medium weight, and light weight

according to both ASTM C90-03[13] and ESS 1292-1/2005[14]. The two criteria that specify the

categorization of weight are the Oven-Dry weight and water absorption. The results are shown figures

5 to 8. The limits of Oven-Dry weight and water absorption are given in table 5.

The average absorption in figure 5 show that all tested specimens provided absorption values less than

208 Kg/m3at tested ages regardless of the type of cement. Figure 6 also show that the use of fully

recycled aggregates also resulted in water absorption lower than 208 Kg/m3at tested ages. Tables 6 and

7 demonstrate that the average unit weight of tested specimens were higher than 2000 Kg/m3.

Consequently, all tested specimens fall in the category of normal weight bricks. Figures 7 and 8

present the effects of the two cooling regimes on average absorption after exposure to the two elevated

temperatures. After exposure to 600°С, specimens were tested for water absorption after being exposed

to two cooling regimes: air and water.

Fig5: Effects of cement types on average absorption

Fig 6: Effects of cement types and recycled aggregates on average absorption

Fig 7: Effects of the two cooling regimes on average absorption after exposure to 300°С

Fig 8: Effects of the two cooling regimes on average absorption after exposure to 600°С

Table 6: Unit weight of tested mixes (*1000)kg/m3

Mix No.

Tested days

& Aggregate type

Coarse

Aggregate

Fine

Aggregate 3 7 14 28

CEM I – 32.5 N Dolomite Sand 2.21 2.15 2.21 2.17

CEM ΙΙ B-L32,5N Dolomite Sand 2.16 2.21 2.21 2.19

CEM ΙΙ A-S32,5N Dolomite Sand 2.20 2.24 2.11 2.16

CEM ΙΙ B-L32,5N Concrete

Rubble Sand 2.10 2.33 2.13 2.09

CEM ΙΙ A-S32,5N Concrete

Rubble Sand 2.07 2.16 2.37 2.50

CEM ΙΙ B-L32,5N Concrete

Rubble

Concrete

Rubble 2.16 2.02 ---- 1.97

Table 7: Unit weight of tested mixes after exposure to elevated temperature (*1000)kg/m3

Mix No.

Temp.

&cooling regimes

Coarse

Aggregate

Fine

Aggregate C◦300

Air

cooling

C◦ 300

Water cooling

C 600◦

Air cooling

◦C ◦ 600

Water cooling

CEM I – 32.5 N Dolomite Sand 2.27 2.23 2.21 2.20

CEM ΙΙ B-L32,5N Dolomite Sand 2.45 2.47 2.50 2.42

CEM ΙΙ A-S32,5N Dolomite Sand 2.19 2.32 2.48 2.41

CEM ΙΙ B-L32,5N Concrete

Rubble Sand 2.45 2.51 2.51 2.42

CEM ΙΙ A-S32,5N Concrete

Rubble Sand 2.33 2.31 2.52 2.39

4- Conclusions

Based on the experimental results obtained from this study, the following conclusions can be drawn:

1) At all tested ages and when virgin aggregates were used, CEM ΙΙ A-S32,5N (mix 3) provided

the highest strengths, while CEM Ι 32,5N (mix 1) yielded the lowest strengths

2) The limit of load-bearing units was met at age 3 days for the three types of cements

3) Mixes which were exposed to 300°С and cooled by air and water met the limit of load-bearing

units regarding both Egyptian Standard Specifications (ESS) and American Society for Testing

and Materials (ASTM).

4) All tested specimens were of normal weight irrespective of cement types, aggregates types,

testing ages, and cooling regimes.

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