The Mechanical Properties of Concrete Incorporating Silica Fume as Partial Replacement of Cement

International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 9, September 2015)

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The Mechanical Properties of Concrete Incorporating Silica Fume as Partial Replacement of Cement

Hanumesh B M1, B K Varun2, Harish B A3

1Post graduate student, University B D T College of Engineering, Davangere, Karnataka, India 2,3Assistant Professor, G M Institute of Technology, Davangere, Karnataka, India

Abstract-- Concrete is the most important engineering material and the addition of some other materials may change the properties of concrete. With increase in trend towards the wider use of concrete for prestressed concrete and high rise buildings there is a growing demand of concrete with higher compressive strength. Mineral additions which are also known as mineral admixtures have been used with cements for many years. Silica fume particles are 100 times smaller than the average cement particle. Its handling and disposal is a point of concern because of the environment concerns. Silica fume is usually categorized as a supplementary cementitious material. These materials exhibit pozzolanic properties, cementitious properties and a combination of both properties. Due to these properties, it can affect the concrete behavior in many ways. In the present work, an attempt has been made to use silica fume as a supplementary material for cement and to evaluate the limit of replacement of cement for M20 grade concrete. The main aim of this work is to study the mechanical properties of M20 grade control concrete and silica fume concrete with different percentages (5, 10, 15 and 20%) of silica fume as a partial replacement of cement.

Keywords-- Silica Fume, Pozzolanic, Mix-Design, Compressive strength, Split Tensile Strength.

I. INTRODUCTION Concrete is one of the most common material used in the

construction industry. In the past few years, many research and modifications has been done to produce concrete which has the desired characteristics. There is always a search for concrete with higher strength and durability. Particularly mineral admixtures are indispensable in production of high strength concrete for practical application. The use of mineral admixtures as a pozzolana has increased worldwide attention over the recent years because when properly used it as certain percent, it can enhance various properties of concrete both in the fresh as well as in hardened states like cohesiveness, strength, permeability and durability. The best mineral admixtures in optimum proportions mixed with OPC improves many qualities of concrete such as lowers the heat of hydration, increases the watertightness, reduces alkali-aggregate reaction, improves workability and resistance to attack by sulphate soils, sea water.

Silica fume, also referred to as micro silica or condensed silica fume, is used as an artificial pozzlanic admixture. It is the product resulting from reduction of high purity quartz with coal in an electric arc furnace in the manufacture of silicon or ferrosilicon alloy. Silica fume rises as an oxidized vapour. It cools, condenses and is collected in cloth bags. It is further processed to remove impurities and to control particle size. Condensed silica fume is essentially silicon dioxide (more than 90%) in noncrystalline form. Since it is airborne material like fly ash, it has spherical shape. It is extremely fine with particle size less than 1 micron and with an average diameter of about 0.1 micron, about 100 times smaller than average cement particles. Silica fume has specific surface area of about 20000m2/kg , as against 230 to 300m2/kg.

II. OBJECTIVES OF THE STUDY The following are the main objective of the study

a) To evaluate the compressive strength of control concrete of grade M20 and silica fume concrete produced by replacing cement in different percentage. b) To evaluate the split tensile strength of control concrete of grade M20 and silica fume concrete produced by replacing cement in different percentage.

III. LITERATURE REVIEW Many researchers have been studied the effect of

replacement of cement by silica fume on strength and durability aspects of concrete.

K.C.Biswal and Suresh Chandra Sadangi their journal entitled “Effect of superplasticizer and silica fume on properties of concrete” (March 2011). Nowadays high strength and high performance concrete are widely used in many civil engineering constructions. To produce them it is required to reduce the water/powder ratio and increase the binder content. Superplasticizers are commonly used to achieve the workability. Silica fume is one of the popular pozzolanas used in concrete to get improved properties.



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The use of silica fume in conjuction with superplastisizers has become the backbone of high strength and high performance concrete. An experimental program has been carried out to study the effect of superplasticizer alone and in conjuction with silica fume on some of the properties of fresh and harden of concrete.

Figure 1: Variation of compressive strength with varying percentage

of SF

The following conclusions may be made from the present investigation of the replacement of cement silica fume and use of superplasticizer on fresh and harden concrete properties. The water cement ratio reduces by 23% in concrete by

using superplasticizer ( 1% by weight of cement) for a constant range of slump 80 to 85mm.

The compressive strength of concrete is increased by use of silica fume upto 20% replacement of cement.

The flexural strength of concrete is increased by use of silica fume upto 15% replacement of cement.

Hassan A. Mohamadienin their journal entitled “The Effect of marble powder and silica fume as partial replacement for cement on mortar” (2012). The possibility of using marble powder and silica fume (S.F) separately as partial replacement of cement on mortar were studied and evaluated based upon the percentage of the partial cement replacement with both marble powder and silica fume separately. Four types of mortar mixture with same workability, cement to sand ratio of 1:3 and water to cementitious materials ratio of 0.4 were prepared marble powder and silica fume used in mixes separately, once as a partial replacement of cement content and another as an addition to the mix proportion. Replacement and addition ratio of both marble powder and silica fume with cement content separately at 0%, 5%, 10%, 15%, 20%, 30% and 50 % by weight were investigated.

The mechanical properties of mortar were measured in terms of compressive strength at 7 and 28 days and it was observed that the strength developments at 7, and 28 days and the highest development rate of compressive strength was observed at 15% replacement ratio for each the marble powder and silica fume separately. Results showed that the compressive strength increased by 31.4%, 48.3% at 7, and 28 days respectively at 15% replacement ratio of silica fume with cement content and in case of replacement marble powder with cement content the compressive strength increased by 22.7%, 27.8% at 7, and 28 days at 15% replacement ratio of marble powder with cement content respectively.

Due to analysis of the tests results, the maximum value for compressive strength was obtained with the use of 15% silica fume as a partial replacement and the percentage of the increasing 48.3%. The compressive strength of mortar is decreased when Silica fumes contents used as a partial replacement with percentage higher than 15%. The compressive strength of mortar increased when Silica fumes contents used as an addition with percentage 5%, 10%, 15% and is almost comparable at percentage higher than 15 %. Using marble powder up to 15% as an additive materials enhancement the compressive strength up to 31.5%. Marble powder can be used as alternative materials for silica fume in mortar.

Faseyemi Victor Ajileye in their papers entitled “Investigations on Microsilica (Silica Fume) As Partial Cement Replacement in Concrete” (January 2012). Studies have been carried out to investigate the possibility of utilizing abroad range of materials as partial replacement materials for cement in the production of concrete. This study investigated the strength properties of Silica fume concrete.

The specific gravity and chemical composition of silica fume and cement were replaced with micro silica from 0 to 25% in steps of 5% by weight, mix proportioning was based on 1:2:4 mix ratio. Cubes (150 x 150 x 150 mm) were produced and cured in a curing tank for 3, 7, 14 and 28 days. The cubes were subjected to compressive strength tests after density determination at 3,7,14 and 28 days respectively. The chemical composition and physical composition of micro silica and cement were determined. Ordinary Portland cement was replaced with silica fume. The total amount of Tricalcium aluminate in the cement was 7.7% and this was above the requirement. (Specified by BS12/EN196:1996),others chemical compositions for silica fume such as SiO2, moisture content, loss of ignition, carbon, > 45 micron, bulk density.

Also % chemical composition and physical properties for SiO2, Al2O3, Fe2O3,CaO, MgO, SO3, Alkalis ( Na2O



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+ 0.658K2O), loss of ignition (Lo1), insoluble residue (IR), Tricalcium, silicate, Dicalcium silicate, CaO / SiO2, chloride, fineness (Blaine air permeability test) in Cm2/g, soundness (mm) were in compliance with BS Standard. The density of the concrete decreased with increased in percentage of micro silica replacement up to 10%. Increase in the level of micro silica fume replacement between 15% to 25% led to a reduction in the compressive strength of hardened concrete. The test was carried out conforming to BS EN: 12390 – 3: 2009 to obtain compressive strength of C30 grade of concrete. The compressive strength of high strength concrete with OPC and silica fume concrete at the age of 3, 7, 14 and 28 days.

Figure 2: Relationship between compressive strength with varying

percentage of micro silica

Cement replacement upto 10% with silica fume leads to increase in compressive strength, for C30 grade of concrete. From 15%, there is decrease in compressive strength for 3,7,14 and 28 days curing period. It was observed that the compressive strength of C30 grade of concrete is increased from 16.15% to 29.24% and decreased from 23.98% to 20.22%. the maximum replacement level of silica fume is 10% for C30 grade of concrete.

IV. MATERIALS AND METHODOLOGY Cement

In this present work Ultratech cement of 43garde ordinary Portland cement (OPC) was used for casting cubes and cylinder for all concrete mixes. The cement was of uniform colour i.e. grey with a light greenish shade and was free from any hard lumps. The various tests conducted on cement are initial and final setting time, specific gravity, fineness and compressive strength.

Testing of cement was done as per IS: 8112-1989. The specific and composition limits of Portland cement are reported in Table 1.

Table. 1: Physical properties of cement

Particulars Experimental result As per standard

Soundness (Le chatlier mould) 1.00 mm 10 mm

Setting time (minutes) Initial set 61min 30min (minimum)

Final set 240min 600min (maximum)

Comp.strength (MPa)

3 days 20.79MPa 16MPa (minimum) 7 days 36.22MPa 22MPa (minimum) 28 days 45.93MPa 43MPa (minimum)

Temperature during testing 27.810C 270C±20C

Fine Aggregate The sand used for this project was locally procured and

conformed to grading zone ІІІ as per IS: 383-1970. The specific gravity of fine aggregate was found to be 2.89. and Fineness modulus 2.3. Water absorption was found to be 1.2%. And free moisture content was 0.36%.

Table 2: Sieve analysis of fine aggregate

Sieve size

(mm)

Weight retained

(gm)

Cumulative Weight

retained, (gm)

Cumulative percentage

retained

Cumulative percentage

passing

4.75 3 3 0.3 99.7 2.36 18 21 2.1 97.9 1.18 172 193 19.3 80.7 0.60 151 344 34.4 65.6 0.30 450 794 79.4 20.6 0.15 165 959 95.9 4.1 Pan 41 1000 100 0

The fine aggregate belongs to zone III (as per IS: 383-1970) F.M. = 231.4/100 = 2.314

Coarse Aggregate Locally available coarse aggregates having the

maximum size of 20mm were used in the present work. The specific gravity of coarse aggregate was found to be

2.82. Water absorption was found to be 0.3%. And free moisture content was 0.0%.



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Silica Fume Silica fume from Sai Dhurga Enterprises, Bangalore,

Karnataka.

Water Potable tap water was used for the preparation of

specimens and for curing specimens.

Mix Design The proportioning of the ingredients of concrete is an

important phase of concrete technology as it ensures quality and economy. In pursuit of the goal of obtaining concrete with desired performance characteristics the selection of component materials is the first step, the next step is a process called mix design by which one arrives at the right combination of the ingredients. The mix design procedure adopted in the present work to obtain M20 grade concrete is in accordance with IS 10262 – 2009.

Table 3: Mix proportions

W/C ratio

Water ( kg/m3)

Cement (kg/m3)

Fine aggregate

(kg/m3)

Coarse aggregate

(kg/m3) 0.52 197 378.85 718.48 1224.97

Concrete mix designation: Table 4:

Concrete Mix Designation

Mix designation Description M0 Control concrete of grade M20 M1 5% Silica fume + 95% Cement M2 10% Silica fume + 90% Cement M3 15% Silica fume + 85% Cement M4 20% Silica fume + 80% Cement

V. EXPERIMENTAL RESULTS Compressive strength test results:

For each concrete mix, the compressive strength is determined on three 150×150×150mm cubes at 7, 28, 56 and 90 days of curing.

The table below gives the overall result of compressive strength of silica fume concrete produced with different percentages of silica fume. The variation of compressive strength in the form of graph as shown in fig 4.

Figure 3: Testing of cubes

Table 5: Overall results of compressive strength

Mix designation

Compressive Strength (N/mm2)

7 Days

28 Days 56 Days 90 Days

M0

18.96 27.70 39.84 40.88

M1

19.03 28.14 39.84 41.03

M2

19.77 29.18 42.21 43.77

M3

15.92 23.25 29.92 32.44

M4

14.66 21.03 24.29 24.44



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05

101520253035404550

0 5 10 15 20

com

pres

sive

str

engt

h in

N/m

m2

SF in percentage

7 days

28 days

56 days

90 days

Figure 4: Overall results of compressive strength Split Tensile Strength Test Result

Test has been conducted after 7, 28, 56 and 90 days of curing. Split tensile is conducted on 150mm diameter and 300mm length cylinders as per IS 5816 – 1999.

The table 6 gives the overall result of split tensile strength of silica fume concrete produced with different percentages of silica fume.

Figure 5: Testing of cylinders

Table 6: Overall results of split tensile strength

Mix designation

Split tensile Strength (N/mm2)

7 Days

28 Days 56 Days 90 Days

M0

1.29 2.54 2.75 2.96

M1

1.41 2.68 2.82 3.10

M2

1.69 3.25 3.32 3.55

M3

1.27 2.47 2.44 2.80

M4

1.10 2.26 2.28 2.49

0

0.5

1

1.5

2

2.5

3

3.5

4

0 5 10 15 20

Split

tens

ile s

tren

gth

in N

/mm

2

SF in percentage

7 days

28 days

56 days

90 days

Figure 6: Overall results of split tensile strength



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VI. OBSERVATIONS AND DISCUSSIOS In the present work the effect of silica fume as partial

replacement of cement on the compressive strength and split tensile strength of concrete is investigated and the following observations were made from the experiment conducted.

At 7, 28, 56 and 90days control concrete achieved a compressive strength of 18.96, 27.70, 39.84 and 40.88N/mm2, where as mix M2 achieved a compressive strength of 19.77, 29.18, 42.21 and 43.77N/mm2. There is a significant improvement in the strength of concrete because of the high pozzolanic nature of silica fume to form more densely packed C-S-H gel and the void filling ability. It can be observed that compressive strength of silica fume replacement from control concrete M2 mix (10% replacement level of silica fume) increases by 4.27%, 5.34%, 5.94% and 7.06% for 7, 28, 56 and 90days compared to control concrete. Beyond 10% replacement there is a decrease in compressive for 7, 28, 56 and 90days. The maximum replacement level of silica fume is 10% for M20 grade concrete.

The split tensile strength of the control concrete increases with the increase in percentage of silica fume at 7, 28, 56 and 90days. Control concrete achieved split tensile strength 1.29, 2.54, 2.75 and 2.96N/mm2, where as M2 mix achieved a split tensile strength of 1.69, 3.25, 3.32 and 3.55N/mm2. As the percentage of silica fume is increased, there is an improvement in packing, i.e., action of it as a filler material resulting in improvement of the interfacial bond between the aggregate-cement matrix. As a result sharp increase in tensile strength is observed. It can be observed that the split tensile strength of M2 mix increases by 31.00%, 27.95%, 20.72% and 19.93% for 7, 28, 56 and 90days. Beyond 10% replacement there is a decrease in split tensile strength for 7, 28, 56 and 90days compared to control concrete.

VII. CONCLUSIONS Based on the limited experimental investigation

concerning compressive strength and split tensile strength of concrete with silica fume as a partial replacement of cement, the following conclusion can be drawn.

1. The compressive strength of concrete is increased by the use of silica fume up to 10% replacement of cement. From 10% there is a decrease in compressive strength.

2. The split tensile strength of concrete is increased by use of silica fume up to 10% replacement of cement. From 10% there is a decrease in split tensile strength.

3. The compressive strength mainly depends on the percentage of silica fume because of its high pozzolanic nature to form more densely packed C-S-H gel.

4. The split tensile strength increases mainly due to improvement in packing, i.e., action of it as a filler material.

5. The optimum percentage of replacement of cement by silica fume is 10% for M20 grade of concrete.

REFERENCES [1] Aditya Dhagat, Manav Mittal (august 2013) “Effect of Microsilica

and Fly ash on the Strength of Concrete”. [2] B. Damodhara Reddy, S. Aruna Jyothy, I.V.Ramana Reddy

(February 2013) “Infuence of Microsilica on the Properties of Ordinary Portland Cement and Portland Slag Cement with and without Super plasticizers”.

[3] Debabrata D.Dutta (October 2013) “Influence of Silica Fume on Normal Concrete”.

[4] Dilip Kumar Singha Roy, AmitavaSil (August 2012) “Effect of Partial Replacement of Cement by Silica Fume on Hardened Concrete’’.

[5] Faseyemi Victor Ajileye (January 2012) “Investigations on Microsilica (Silica Fume) As Partial Cement Replacement in Concrete”.

[6] Gambhir M L, Reprint 2010, “Concrete Technology”, TataMcGraw Hill publishing company Ltd., NewDelhi.

[7] Hassan A. Mohamadienin (2012) “The Effect of marble powder and silica fume as partial replacement for cement on mortar”.

[8] IS 10262: 2009 (Specifications for concrete mix design). [9] IS 456: 2000 (Plain and reinforced concrete - code of practice). [10] IS 2386 (part 3): 1963 (Methods of test for aggregates for concrete). [11] IS 383: 1970 (Specification for coarse and fine aggregate). [12] IS 516: 1959 (Specifications for compressive strength). [13] IS 5816: 1999 (Specifications for split tensile strength). [14] IS 8112: 1989 (Specifications for 43 grade ordinary Portland

cement). [15] K.C.Biswal and Suresh Chandra Sadangi (March 2011) “Effect of

superplasticizer and silica fume on properties of concrete”. [16] M.S Shetty,Reprint 2009, “Concrete Technology”, S.Chand &

company Ltd., New Delhi. [17] Sai Dhurga Enterprises, Imports & Exporters, Bangalore. [18] T.Jeevetha, Dr.S Krishnamurthy and G.S.Rampradheep (April 2014)

“Study on Strength Properties of Self-Compacting Concrete with Micro Silica”.

The Mechanical Properties of Concrete Incorporating Silica Fume as Partial Replacement of Cement

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