EFFECT OF NANO SILICA AND SILICA FUME ON DURABILITY ......silica & silica fume have also been...

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International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 2, February 2018, pp. 115–129, Article ID: IJCIET_09_02_013

Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=9&IType=2

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

© IAEME Publication Scopus Indexed

EFFECT OF NANO SILICA AND SILICA FUME

ON DURABILITY PROPERTIES OF HIGH

PERFORMANCE CONCRETE

Anil Kumar Nanda*, Prem Pal Bansal and Maneek Kumar

Department of Civil Engineering, Thapar University, Patiala, India

* Corresponding author

ABSTRACT

During the manufacturing process of cement, when limestone and clay are crushed

and heated at high temperature, there is emission of global warming gasses including

carbon dioxide (CO2) into the atmosphere. The current atmospheric concentration of

CO2 has reached an alarming high value to the tune of 410 ppm (April, 2017), it has

become obligatory to use a Green concrete to decrease CO2 emission from cement

industry. Aim of the paper is to highlight the utilization of nano silica in high

performance concrete in order to reduce the environmental pollution and to increase

the durability properties. In this Experimental work, the cement was partially replaced

by nano silica with the percentage of 2%, 3% & 4% and replacement level of silica

fume was kept constant at 8% for four different water cement ratios (W/C). The

samples were casted and tested for durability properties (Abrasion and Rapid chloride

penetration test) of high performance concrete for different ages along with Scanning

Electron Microscopy and Energy Dispersive Spectroscopy test. The results were

statistically analyzed. The experimental results show that the best results of Abrasion

and Rapid chloride penetration test were found at 0.30 W/C ratios and at the

replacement level of 4% of nano silica and 8% silica fume for 56 days of curing for

0.30 W/C ratios. The Scanning Electron Microscopy (SEM) and Energy Dispersive

Spectroscopy (EDS) test results showing the level of Ca (OH)2 in plain concrete and

consumption level of Ca(OH)2 along with level of CSH in concrete containing nano

silica & silica fume have also been presented. The results of all the four W/C ratios

have been found statically significant. The results show that the use of nano silica and

silica fume as replacement of cement not only makes the concrete more durable

against the environmental agencies but also reduces the emission of CO2 during the

production of cement. It also solves the waste disposal problem along with saving of

the natural resources.

Keywords: Carbon Dioxide, Durability Properties, High Performance Concrete, Nano

Silica, Silica Fume.

Effect of Nano Silica and Silica Fume on Durability properties of High Performance Concrete


Cite this Article: Anil Kumar Nanda, Prem Pal Bansal and Maneek Kumar, Effect of

Nano Silica and Silica Fume on Durability properties of High Performance Concrete,

International Journal of Civil Engineering and Technology, 9(2), 2018, pp. 115–129.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=9&IType=2

1. INTRODUCTION

The concrete is a most important component of the construction industry. 90% of the

construction globally, is done with concrete, for which huge amount of cement is required.

Cement manufacture contributes CO2 to the atmosphere when calcium carbonate is heated,

producing lime and carbon dioxide. CO2 is also produced by burning the fossil fuels that

provide the heat for the cement manufacture process. It is estimated that the cement industry

produces around 5 per cent of worldwide man-made CO2 emissions, of which 50 per cent is

produced from the chemical process itself, and 40 per cent from burning fuel to power that

process. The amount of CO2 emitted by the cement industry is more than 900 kg of CO2 for

every 1000 kg of cement produced. For this, the massive amount of natural resources are

consumed and lot of CO2 is emitted into the atmosphere, which affects the green houses

besides erosion caused by weathering agencies. Nano materials such as nano silica along with

the conventional building material provide answer to these problems to a certain level.

New nano-silica (NS) can be produced in high quantities and for low prices that allows for

a mass application in concrete. It may replace cement in the mix, which is the costly and

environmentally unfriendly component in concrete. The use of nano silica makes concrete

economical and reduces the CO2 footprint of the produced concrete products. The nano silca

will, additionally, also increase the product properties of fresh concrete like workability and

the properties in hardened state too, thus enabling the development of high performance

concretes for extreme environmental conditions. That means that a concrete with better

performance and, lower costs can be designed [1]. The influence of nano silica particles on

the mechanical properties and durability of concrete through measurement of compressive and

tensile strength, water absorption and the depth of chloride penetration. It was observed that

the compressive and tensile strength increased in presence of nano silica, which indicates the

pozzolanic activity of nano silica. Improvement in interfacial transition zone was noted and

also water absorption, capillary absorption and distribution of chloride ion test results indicate

that the nano silica concrete has better permeability resistance than the normal concrete [2].

The water absorption, capillary absorption and distribution of chloride ion tests indicated that

the nano-silica concrete has better permeability resistance than the normal concretes [3]. The

Silica fume has been recognized as a pozzolanic and cementitious admixture which is

effective in enhancing the mechanical properties to a great extent. The pozzolanic reaction

result in a reduction of the amount of CH in concrete, and silica fume reduces porosity and

improves durability. It accelerates the dissolution of CH and formation of CSH with its

activity being inversely proportional to the size, and also provides nucleation sites for CSH. It

is responsible for an additional increase in strength and chemical resistance and decrease in

water absorption [4]. The recent developments and present state of the application of silica

fume and nano silica for sustainable development of concrete industry. Limited work is done

on use of nano silica and silica fume in paste, mortar and concrete and whatever work is

available, it is highly contradictory about their influence on mechanical strength development

and durability properties. Various literatures have been reviewed to understand the influence

of micro and nano silica on fresh, hardened and micro structural properties of paste, cement

mortar and concrete. Taking advantage of nanostructure and microstructure characterization

tools and materials, the simultaneous optimal use of silica fume and nano silica will create a

new concrete mixture that will result in long lasting concrete structures in the future [5]. The

Anil Kumar Nanda, Prem Pal Bansal and Maneek Kumar


enhancement of strength was not only because of pore filling effect, but also by the

accelerated cement hydration due to their higher reactivity of nano silica. Moreover, the water

and capillary absorption results revealed significant decrease by the addition of blended nano

silica and silica fume for the binder content. According to SEM microstructure studies, more

refined microstructure and smaller pores were achieved by the addition of nano silica and

silica fume, which can led to enhancement of mechanical, durability and micro structural

properties of HPSCC [6]. Nano Silica has been found to increase the strength, flexibility,

workability and durability of concrete. The nano silica particles increase the viscosity of the

fluid phase of concrete and fill the voids between cement grains. It reacts with CH and results

in more CSH. Almost all the properties of concrete are controlled by CSH which is a

nonporous, nano-structured material [7]. Combining the management of wastes and

nanotechnology can lead to accessing both performances of structural components as well as

reduction of the harmfulness of hazardous by-products. The application of nanotechnology in

the civil engineering related industry can play an important role in the quality of building

materials (strength, durability and lightness) [8]. The addition of nanoparticles improves the

pore structure of concrete. On the one hand, nanoparticles can act as a filler to enhance the

density of concrete, which leads to reduction in the porosity of concrete. On the other hand,

nanoparticles not only act as an activator to accelerate cement hydration due to their high

activity, but also act as a kernel in cement paste which makes the size of CH crystal smaller

and the tropism more stochastic [9]. The significant improvement was observed in mixtures

incorporating nano-silica in terms of reactivity, strength development, refinement of pore

structure and densification of interfacial transition zone. This improvement can be mainly

attributed to the large surface area of nano-silica particles, which has pozzolanic and filler

effects on the cementitious matrix. Micro-structural and thermal analyses indicated the

contribution of pozzolanic and filler effects to the pore structure refinement depended on the

dosage of nano-silica [10]. The nano silica can improve the performance of cement based

materials matrix through increased production of CSH gel due to pozzolanic reaction and

reduced amount of CH. It can also act as micro and nano filler [11]. Conventional concrete

improved by applying nanotechnology aims at developing a novel, smart and environment-

friendly construction material towards the green structure [12]. Application of

nanotechnology is an effective way to reduce environmental pollution and improve durability

of concrete [13].

Now a day’s lots of work is going on nano materials in concrete construction individually

and in combination with silica fume but its application and effect has not been fully

understood yet. In the present work, cement in concrete has been replaced with both nano

silica & silica fume and compared with normal concrete. Due to the fineness of nano-

materials, it reacts more actively and refines the pores of the concrete in a better ways. The

only problem for using such materials is that, due to its large specific surface area, it increases

the water demand and reduces the workability. This problem can be solved by using

superplasticizer. Again to minimise dose of superplasticizer, we add a constant dose of silica

fume. Silica fume being coarser than nano silica has lesser spherical surface area and hence

has less water demand than nano silica. Secondly, the nano silica is not easily available in the

market and is more costly than silica fume. Also, even a little amount of nano particles can

react very well with calcium hydroxide (CH) to produce the stable Calcium Silicate Hydrate

(CSH) which ultimately increases the durability of the concrete. Therefore, this experimental

study is aimed to investigate the durability characteristics, specifically rapid chloride

penetration and abrasion test of concrete by incorporating different dosages of nano silica

along with silica fume as partial replacements of cement.



The other purpose of use of nano silica for the preparation of high performance concrete

(HPC) is to diminish Greenhouse gas discharge and also to decrease the use of natural

resources such as limestone and clay that are being consumed for the improvement of human

mankind. Use of waste materials in concrete also prevents the huge area of land that is used

for the storage of waste resources which leads to environmental pollution. Nano silica

concrete will result in the sustainable improvement without destruction of natural resources.

The SEM and EDS test was conducted to know the consumption level of CH in plain

concrete and formation of CSH in concrete with all levels of replacement. The XRD tests

have also been conducted to study the effects on the concrete microstructure. Superplasticizer

was used as water reducing agent to maintain workability in medium range i.e. 0.85-0.95.

2. MATERIALS AND METHODS

2.1. Properties of Materials:

Ordinary Portland cement of 43 grade (Ultra tech) conforming to BIS: 8112 [14] was used in

this experimental work. The cement used had a specific gravity of 3.10, with a Blaine

specific surface of 3050 cm2/gm. The compressive strength of OPC used after 7 days & 28

days was 33.78N/mm² & 47.36N/mm², respectively. Crushed stone aggregates of 20 mm

& 12.5mm sizes, in equal proportions, having specific gravity of 2.64 and 2.62, respectively,

were used as coarse aggregates. The crushed stone sand, conforming to zone-II as per BIS:

383 [15], having specific gravity 2.64 were used as fine aggregate in the concrete mix. Nano

silica and silica fume used in this study were commercially available and were supplied by

Bee Chems & Orkla India (Pvt) Ltd (Brand Name: Elkem Micro-silica 920-D), respectively.

The physical and chemical properties of silica fume and nano-silica are given in Table 1.

Superplasticizer, by the brand name Master Glenium Sky 8777, was obtained from BASF

construction chemicals (India). The superplasticiser used is a second generation

polycarboxylic etherpolymer has a relative density 1.10 at 25°C. Normal tap water was used

through-out the experimental work.

2.2. Mix Design for Different Water Cement Ratios:

Concrete mixes, as per BIS: 10262 [16] guidelines were designed for four different water-to-

binder (the sum of the cement, nano silica & silica fume) ratios of 0.30, 0.34, 0.38 & 0.42

respectively, in the experimental work undertaken. The workability of the concrete mixes was

maintained in medium range with the compaction factor lying in the range 0.85 to 0.95. The

proportions of the constituent materials so obtained for control concrete mixtures

corresponding to the four water-cement ratios are given in Table 2. Herein, A0, B0, C0 & D0

denote plain concrete mixes. The mixes A2, B2, C2, D2; A3, B3, C3, D3 and A4, B4, C4, D4

denotes concrete mixes containing nano silica at the replacement level of 2%, 3% & 4%,

respectively, for all the four water-to-binder ratios with silica fume percentage kept constant

at replacement level of 8%.

2.3. Specimen Preparation for tests:

Firstly, the coarse aggregates, which were saturated surface dry, were placed in the mixer.

The binder (cement only in case of control mixes and cement & silica fume for other mixes

already thoroughly manually mixed) and fine aggregates were added and mixed for about a

minute. Subsequently 70% of total water is mixed for nearly 3 min. After the initial mixing is

complete remaining 30% of water, which was premixed with the pre-calculated

superplasticizer dosage (from requirements of workability) and nano silica in two equal parts,

was added and mixing was done for another one and a half to two minutes. The compaction



factor test was conducted to check the workability, and then finally, the fresh concrete was

poured into the well-oiled cylinders moulds of size 100 x 200 mm for rapid chloride

permeability test and 70.6 x 70.6 x 25 mm for abrasion test. After pouring the concrete, an

external vibrator was used to facilitate the compaction and decrease the amount of air bubbles.

All the specimens were de-moulded after 24 h and then put in water tank for curing at a

temperature of 27±2°C.

2.4 Rapid chloride penetration:

The rapid chloride penetration test was performed in accordance with ASTMC 1202-12[17].

The specimen of rapid chloride penetration test has a nominal diameter of 100 mm and

thickness of 50 mm cut from the centre of cylindrical samples. For all the designated mixes

and for each of the testing ages, 10 samples were cast and the average value of results is given

in Table 3.

2.5 Abrasion test:

The abrasion test was performed in accordance with BIS: 1237 [18]. The specimen of

abrasion test has 70.6 x 70.6 x 25 mm in size. Then, the samples were oven dried for a given

ages at temperature 1100± 5

0 C before performing the test. For all the designated mixes and

for each of the testing ages, 10 samples were cast and the average value of results is given in

Table 3. The average loss in thickness was calculated from the following formula:

t= (W1- W2) V1/ (W1 Χ A)

Where t= average loss in thickness in mm

W1=initial mass of specimen in g

W2= final mass of the abraded specimen in g

V1= initial volume of specimen in mm3

A= surface area of the specimen in mm2

2.6 Preparation of samples for XRD test:

As the aggregate-paste interfacial zone is considered to be the most sensitive area within

concrete, contributing to the early commencement of the concrete failure process, the XRD

test were performed on samples taken from the core of the concrete cubes after 7 & 28 days of

curing. The testing was carried out in accordance with ASTM-D 3903-03[19] for the collected

samples. In order to find out the degree of interaction between CH and nano silica & silica

fume and also to observe improvement in the interface structure of concrete. The test was

conducted on Expert Pro of analytical (Netherland) equipment.

2.7 Preparation of samples for SEM test:

As the aggregate-paste interfacial zone is considered to be the most sensitive area within

concrete, contributing to the early commencement of the concrete failure process, the SEM

test was performed on samples taken from the core of the concrete cubes after 7 and 28 days

of curing. The testing was carried out in accordance with ASTM-C1723-10[20] for the

collected samples in order to find out the degree of interaction between CH and NS & SF and

also to observe improvement in the interface structure of concrete. The test was conducted on

JSM-6510LV of JEOL equipment.



Table 1 Chemical compositions and physical properties of Silica fume & Nano silica

Material Chemical composition (wt %)

SiO2 Al2O3 Fe2O2 CaO MgO K2O Na2O

SF 93.80 0.206 0.096 0.426 0.222 0.337 0.107

NS 99.90

Physical properties

Specific

gravity

Solids

(%wt/wt) pH

Particles

Size (nm)

Specific surface

(m2/gm)

Viscosity

(seconds)

SF 2.26 18

NS 1.20-1.22 30-32 9-10 8-10 275-300 12-13

Table 2 Mixture proportions for control concrete mixes

Water-

cement

ratio

Water

(kg/m3)

Cement

(kg/m3)

Fine

aggregates

(kg/m3)

Coarse

Aggregate – I

(20mm)

(kg/m3)

Coarse

aggregate – II

(12.5mm)

(kg/m3)

Superplasticizer

(kg/m3)

0.30 113.00 450 615.00 653.455 653.455 9

0.34 128.12 450 602.34 639.99 639.99 9

0.38 143.20 450 609.84 619.08 619.08 9

0.42 158.27 450 613.06 617.57 617.57 9

2.8. Curing conditions for specimens:

All the specimens of concrete were demoulded after 24 h and then put in water tank for curing

at a temperature of 27±2°C.

3. RESULTS AND DISCUSSION

3.1. Rapid Chloride Penetration Test:

Rapid chloride penetration test results given in Table 3 indicates that increase in nano silica

content by weight 2%, 3%, 4 % (keeping 8% of silica fume constant by weight) lead to an

increase in the chloride ion penetration resistance of concrete of series-A at all stages as

compared to normal concrete (without nano silica and silica fume). The increase in the

chloride ion penetration resistance is attributed to increase in the amount of CSH and increase

in the pace of the hydration of tricalcium silicate (C3S) and dicalcium silicate (C2S). The

spaces in CSH crystal lattic are filled due to its high spherical surface and fineness. In other

words, Nano silica and silica fume has better pore refinement and makes the concrete more

compact and dense which ultimately increases the resistance to the chloride ion intrusion. In

rapid chloride penetration test, nano silica acts more as filler than its pozzolanic activity. For

example, the chloride ion penetration resistance of A2, A3 and A4 was less by 25, 29 and 36 %

for 7 days, by 25, 33 and 36 % for 28 days and by 24, 36 and 38 % for 56 days in comparison

to A0 [Ghasemi et.al [21], Chen et.al [22]]. The results have been statistically analyzed with

GraphPad Prism and were found significant at P < 0.05 (P=0.0075, P<0.0001) with

R2=0.9144.

The similar trend was also found for B, C and D series. For B-series, the chloride ion

penetration resistance of B2, B3 and B4 was less by 14, 27 and 39 % for 7 days, 16, 19 and 23

% for 28 days and 16, 22 and 26 % for 56 days in comparison to B0. For C-series the chloride

ion penetration resistance of C2, C3 and C4 was less by 17, 29 and 41 % for 7 days, 14, 22 and



32 % for 28 days and 7, 15 and 30 % for 56 days in comparison to C0. For D-series the

chloride ion penetration resistance of D2, D3 and D4 was less by 4, 23 and 34 % for 7 days, 05,

23 and 28 % for 28 days and 17, 25 and 34 % for 56 days in comparison to D0. It shows that

the optimum level of replacement for most of the W/C ratio is 4 % of nano silica & 8 % of

silica fume at all replacement levels. The results of B, C and D series have also been

statistically analyzed with GraphPad Prism and were found significant at P < 0.05.

3.2. Abrasion Test:

Abrasion test results given in Table 3 indicates that increase in nano silica content by weight

2%, 3% 4 % (keeping 8% of silica fume constant by weight) lead to an decrease in average

loss in thickness of concrete of series-A at all stages as compared to normal concrete (without

nano silica and silica fume). For example, the decrease in average loss in thickness of A2, A3

and A4 was less by 8, 8 and 43 % for 7 days, by 26, 34 and 54 % for 28 days and by 11, 44

and 56 % for 56 days in comparison to A0. The first cause of reduction in abrasion is that with

the addition of nano silica and silica fume, during hydration of cement, the reaction takes

place between nano silica and silica fume and Ca (OH)2 which increases the amount of CSH

and accelerates the pace of hydration of tricalcium silicate (C3S) and dicalcium silicate (C2S)

resulting in a dense concrete.

The second cause of reduction in abrasion is pozzolanic effect, which combines the

elements of nano silica and silica fume with Ca(OH)2 due to which bond strength is increased

which further augments in better compressive strength and less abrasion of concrete. The

filling effect of nano silica also leads to the decrease in average loss in thickness of concrete

samples [Jalal et.al (2012) [6], Kontoleontos et al [23], Nazari and Riahi [24]].

It is also

observed that there was a decrease in average loss in thickness of concrete with the decrease

in water cement ratio [Rahmani et.al [25]]. The results have been statistically analyzed with

GraphPad Prism and were found significant at P < 0.05 (P=0.0093, P=0.0018) with

R2=0.8370.

The similar trend was also found for B, C and D series. For B-series, the decrease in

average loss in thickness of B2, B3 and B4 was less by 9, 17 and 23 % for 7 days, 12, 15 and 27

% for 28 days and 10, 17 and 25 % for 56 days in comparison to B0. For C-series the decrease

in average loss in thickness of C2, C3 and C4 was less by 4, 15 and 23 % for 7 days, 5, 17 and

24 % for 28 days and 6, 16 and 21 % for 56 days in comparison to C0. For D-series the

decrease in average loss in thickness of D2, D3 and D4 was less by 6, 12 and 22 % for 7 days,

9, 14 and 23 % for 28 days and 14, 19 and 23 % for 56 days in comparison to D0. It shows

that the optimum level of replacement for most of the W/C ratio is 4 % of nano silica & 8 %

of silica fume at all replacement levels. The results of B, C and D series have also been

statistically analyzed with GraphPad Prism and were found significant at P < 0.05.

3.3. X-Ray Diffraction Test:

The XRD test gives the amount of different type of constituents existing in concrete

specimens. The present XRD data was indexed with standard data base of international centre

for diffraction data (ICDD). A number of ICDD cards are available showing crystal structure

of CSH, such as ICDD card no 01-081-1987 shows orthorhombic structure of calcium silicate

hydrate Ca2(SiO4)(H2O). As it is very clear from the XRD Fig. 1 that in B- series, there was

an increase in the amount of CH and CSH with the addition of Nano silica and Silica fume if

samples compared with controlled mix after 7 days of curing. There was an increase in the

amount of CH at 2θ=18°,37° for all 2%, 3% and 4 % replacement level of nano silica by

keeping Silica fume



Table 3 Abrasion and Rapid chloride penetration test values of high performance concrete without &

with nano silica and silica fume

Sample

Abrasion (Average loss in thickness (t) in

mm) (%)

Rapid chloride penetration (Charge

passed in coulombs) (%)

7 days 28 days 56 days 7 days 28 days 56 days

A0 0.247(100) 0.230(100) 0.190(100) 1247(100) 1190(100) 1142(100)

A2 0.228(92) 0.170(74) 0.170(89) 936(75) 890(75) 869(76)

A3 0.228(92) 0.152(66) 0.107(56) 887(71) 793(67) 734(64)

A4 0.140(57) 0.105(46) 0.083(44) 803(64) 758(64) 708(62)

B0 0.397(100) 0.342(100) 0.310(100) 1584(100) 1085(100) 974(100)

B2 0.360(91) 0.302(88) 0.280(90) 1357(86) 915(84) 818(84)

B3 0.330(83) 0.292(85) 0.257(83) 1153(73) 880(81) 763(78)

B4 0.307(77) 0.250(73) 0.232(75) 969(61) 832(77) 720(74)

C0 0.493(100) 0.460(100) 0.430(100) 1680(100) 1298(100) 1136(100)

C2 0.473(96) 0.438(95) 0.403(94) 1395(83) 1122(86) 1053(93)

C3 0.417(85) 0.383(83) 0.360(84) 1188(71) 1014(78) 967(85)

C4 0.378(77) 0.348(76) 0.340(79) 998(59) 887(68) 795(70)

D0 0.560(100) 0.520(100) 0.483(100) 1765(100) 1354(100) 1271(100)

D2 0.528(94) 0.473(91) 0.417(86) 1704(96) 1288(95) 1049(83)

D3 0.493(88) 0.448(86) 0.390(81) 1354(77) 1042(77) 949(75)

D4 0.438(78) 0.402(77) 0.370(77) 1160(66) 977(72) 853(66)

constant at 8% and increase in the level of CSH was found at 2θ= 30° for 2%, 3% and 4 %

replacement level of nano silica by keeping Silica fume constant at 8%. These facts are also

well supported by EDS test. According to EDS test (Figure 5), there was an increase in the

CH amount after 7 days i.e. 7.17%, 5.93% and 0.32 % with the 2%, 3% and 4 % replacement

level of nano silica by keeping Silica fume constant at 8%. Senff et.al [26] also supported this

fact by referring that the nano silica addition contributed to an increased production of CH at

early age compared with samples without nano silica. For 28 days, XRD Fig. 2 shows that in

B series, there was a decrease in the amount of CH and at the same time there was an increase

in amount of CSH with the addition of Nano silica and Silica fume, when compared with

controlled mix after 28 days. The decrease in the amount of CH was found at 2θ= 18°, 34°

and increase in the level of CSH was found at 2θ= 27° for 2%,3% and 4 % replacement level

of nano silica by keeping Silica fume constant at 8%. As per EDS test, both the silica’s

consumes 57.45 %, 40.71% and 44.26 % of CH and converts it into CSH at all the three levels

of replacement (2%, 3% and 4 % replacement level of nano silica by keeping Silica fume

constant at 8%). According to EDS test (Fig.5 and 6), there was an increase in the CH amount

after 7 days but it was decreased after 28 days. It is due to fact that nano silica has high

specific surface which actively react with the CH crystals existing within the concrete and

produces the CSH and consequently decreases the amount of CH crystals also reported by

Esmaeili and Andalibi [27].

Same trend was also found for A, C, and D series. The increase in the amount of CH was

found at 2θ= 37°for A series for all three replacement levels, 2θ=34°,37° for C series for all

three replacement levels , 2θ= 34° for D series for all three replacement levels and increase in

the level of CSH was found at 2θ= 21°,27°and 21° for A series, 2θ= 21°,27°,30° for C series ,

2θ=30° for D series with 2%, 3% and 4 % replacement level of nano silica and by keeping

Silica fume constant at 8% after 7 days of curing. The decrease in the amount of CH was

found at 2θ= 18°, 34° for A series, 2θ= 18°and 37°, 18° and 34°, 18° and 34° for C series, 2θ=



18°and 37°, 18°and 37°, 18°and 34° for D series and increase in the level of CSH was found

at 2θ= 27° for A series for all replacement level, 2θ=29°,27°and29° for C series for all level

of replacement, 2θ=29°,29°and 29° for D series for 2%, 3% and 4 % replacement level of

nano silica and by keeping Silica fume constant at 8% after 28 days of curing. It was also

found that there is an increase in the amount of CH and CSH with the increase in age of

specimens of all the four series of controlled mix. Chow and Barbhuiya [28] concluded that

the XRD analysis showed that CSH and CH of the control mix continued to increase with the

age as a result of the continuation of hydration until 28 days of curing age.

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CH

Figure 1 XRD Test of concrete for W/C 0.34 after 7 days without & with Nano Silica & Silica fume

(SN-5)without NS & SF, (SN-6) with 2%NS & 8 % SF, (SN-7) with 3 %NS & 8 % SF, (SN-8) with

4%NS & 8 % SF.



10 20 30 40 50 60 70 80 900

1000

2000

3000

4000

5000

Inte

nsit

y (

cts

.)

2 Theta (o)

SN-17

CS

HC

SH

CH

CH

CH

CS

H

10 20 30 40 50 60 70 80 900

1000

2000

3000

4000

5000

Inte

nsit

y (

cts

.)

2 Theta (o)

SN-18

CS

HC

SH

CH

CH

CH

CS

H

10 20 30 40 50 60 70 80 900

1000

2000

3000

4000

5000

CS

HC

SH

CH

CH

CH

Inte

ns

ity (

cts

.)

2 Theta (o)

SN-19

CS

H

10 20 30 40 50 60 70 80 900

1000

2000

3000

4000

5000

Inte

ns

ity

(c

ts.)

2 Theta (o)

SN-20

CS

HC

SH

CH

CH C

H

CS

H

Figure 2 XRD Test of concrete for W/C 0.34 after 28 days without & with Nano Silica & Silica fume

(SN-17)without NS & SF, (SN-18) with 2% NS & 8 % SF, (SN-19) with 3 %NS & 8 % SF, (SN-20)

with 4%NS & 8 % SF.

3.4 Scanning Electron Microscope Test:

The SEM test was performed on normal concrete and concrete containing Nano silica and

silica fume with various levels of replacement after curing of 7 & 28 days respectively. For B-

series, the SEM test shows that the microstructure of the concrete containing Nano silica &

silica fume is denser and homogeneous than that of plain concrete. The high reactivity of

Nano silica, which is due to its high spherical surface and fineness also contributed to increase

the hydration and improve the microstructure of concrete. The EDS test (Energy Dispersive

Spectroscopy) was also performed along with SEM test which reveals the level of CH in plain

concrete and the consumption level of CH along with level of CSH at all levels of concrete

containing nano silica & silica fume. It was also evident from Fig.5 and 6 of EDS test and was

already mentioned in the XRD test. The silica reacts with CH to produce CSH due to

acceleration of hydration of tricalcium and diacalcium, which makes the concrete denser &

homogeneous as it is evident if we compare Fig. (b), (c) & (d) with Fig. (a) of Fig. 3 and 4

and as was also reported by several other researchers such as Jalal et.al [6], Esmaeili and

Andalibi [27], Quercia et.al [29], Li et.al [30], Jo et.al [31], Qing et.al [32]. The consumption

level of CH by NS and SF was more at 28 days of curing sample as compared to that of 7

days samples. A similar trend was also found for A, C and D series of mixes.



The results of the study indicate that nano silica has very fine particle size which fills the

pores of aggregates in a better way and increases bond strength between cement paste &

aggregate. The bond strength increases the resistance to abrasion and chloride ions penetration

of concrete. The nano silica concrete can be used where the high performance concrete is

required and durability is the problem i.e. wears of hard (concrete) roads, structures in the

coastal areas and reduce the maintenance cost of the structures. Moreover, the use of nano

silica as replacement of cement saves the natural resources and reduces the emission of CO2

during the production of cement. It also solves the waste disposal problem.

Figure 3 SEM Test of concrete for W/C 0.34 after 7 days without & with Nano Silica & Silica fume

(a)without NS & SF (b) with 2%NS & 8 % SF (c) with 3 %NS & 8 % SF (d) with 4%NS & 8 % SF.

Figure 4 SEM Test of concrete for W/C 0.34 after 28 days without & with Nano Silica & Silica fume




Figure 5 EDS Test of concrete for W/C 0.34 after 7 days without & with Nano Silica & Silica fume


Figure 6 EDS Test of concrete for W/C 0.34 after 28 days without & with Nano Silica & Silica fume




4. CONCLUSION:

• According to results of SEM test, the structure of the concrete consisting Nano silica

and silica fume seems to be more uniform and denser in comparison to controlled

concrete.

• The XRD analysis showed that there was an increase in the level of CH and CSH with

all replacement level of nano silica and silica after curing period of 7 days. But after

curing of 28 days, there was an enhancement in level of CSH at the cost of decrease in

the level of CH at all levels of replacement.

• According to the test results, the joint application of Nano silica and Silica fume

would lead to an enhancement in durability (abrasion and rapid chloride penetration)

of concrete at all level of replacement of cement and at all curing ages in comparison

with that of controlled concrete.

• With age, the abrasion resistance of concrete mix consisting nano silica and silica

fume at all replacement levels as well as controlled concrete mixes has increased.

• The lower values of RCPT test reveal that it has high resistance to chloride ion

penetration of concrete consisting nano silica and silica fume at all replacement levels

at all ages.

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EFFECT OF NANO SILICA AND SILICA FUME ON DURABILITY ......silica & silica fume have also been...

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