A Study of Micro-Silica as a Partial Replacement of Cement in Concrete

A Study of Micro-Silica as a Partial Replacement of Cement in Concrete

1Assistant Professor, Civil Engineering Department, 2,3,4,5,6 Students, B-tech, Civil Engineering, Government College of Engineering Jalgaon-425001[MS]India ***

Abstract - Concrete is widely used material in the field of construction and also replacement or by doing addition of other material may change the properties of concrete. Now a days use of concrete is increased for high rise building and due to that there is increase in demand of concrete with higher compressive strength, also one of expensive ingredient in concrete is cement and to make the concrete mix economical it should be replaced with any other cheap material hence in this experiment we are going to do partial replacement of cement with the cheap material like condensed silica fume to increase the compressive strength and workability of concrete. In this experiment we will take various proportion, 5%,10%,15% of adding micro silica by the mass of cement in concrete in mix design of M25, M30 and M35 grade of concrete as per IS code.

Key Words: Condensed silica fume/ micro silica/ silica fume, Compressive strength, Concrete mix.

1.INTRODUCTION

The concrete is mostly used material for construction anystructureforexampledams,roadspavements,tanks etc. Concrete mixture is consist of cement, sand, coarse aggregate and water. The process of selecting suitable ingredients of concrete and determining their relative amount with objective of producing a concrete of required strength durability and workability as economically as possible is termed as concrete mix design. In the concrete mix design cement is the costly material so it should be replaced by any other cheap material.

Whilereplacingthecementthecareshouldbetakenthat the strength of concrete is not reduced. The micro silica alsoknownassilicafumeorcondensedsilicafumeisthe good replacement of cement in the concrete mix design. Thesilicafumeisabyproductofsiliconandferrosilicon alloyproduction.Itisanultrafinepowder.

Hence when it is used in concrete to fill the spaces between the cement particles and between the cement pastematrixandaggregateparticlesanditactasa filler andcementitious material.Hencebyusingsilica fumeis concrete the voids are also reduced. For replacement of cement generally cheaper materials are selected.

Accordingtothatmicrosilicaischeaperthanthecement hence it is a very good replacement. And also by doing thereplacementofcementwithmicrosilicathestrength ofconcreteisalsoincreased.

2.LITERATURE REVIEW

GhutkeandBhandari(2014)

The influence of micro silica on concrete was examined in this study. The result showed that micro silica is a good for partial replacement of cement. The strength was increased when cement was replaced with micro silica. Concrete reduces its workability as percentage of micro silica is increased. The optimum compressive strength can be obtained in 10% replacement of micro silica. As strength of 15% replacement of cement by microsilica ismorethannormal concrete.Theoptimum cement replacement percentage by micro silica varies from10%to15%.

Hanumesh,VarunandHarish(2015)

In this study it is observed the mechanical properties of concrete when partial replacement of cement is done with micro silica. The main aim of this work is to study mechanical properties of M20 grade concrete when cement is replaced with silica fume at different percentages (5,10,15 and 20). The results showed that strengthofconcreteisincreasedwhen10%replacement of cement is done with micro silica. Above 10% replacement of cement with silica fume it is observed that there is decrease in compressive strength. Hence, optimum percentage of replacement of cement by silica fumeis10%forM20gradeofconcrete.

3.METHODOLOGY

The main objective of mix design is to decide the properties of material which we are going to use in concrete so that concrete will be produced of required properties.Anotherobjectiveof mixdesignistoachieve the desired workability of fresh concrete and also to obtain minimum strength at the hardened stage. Mix designisalsousedtoproducedconcreteeconomicallyso thatwastagewillbeavoided.

Material used for mix design

1. Cement - Ambuja brand cement was used of PPC53grade.

2. Coarse aggregate -20mmand12.5mmsizeof coarseaggregatewasusedinthisexperiment.

3. Fine aggregate - Sand passing through 2.36 mmofISsievewasusedinthismixdesign.

4. Micro-Silica - Black coloured micro-silica was used in this experiment. Spherical partical of micro-silica was less than 1mm in diameter. Specificgravityofmicro-silicawas2.36

5. Admixture -ConplastSP430whichisfreefrom chloride was used. According to brouchre SP430 0.5-2% by weight of cement can be addedinmixdesign.

6. Water - Clean, Potable water was used in mix design.

4.CONCRETE MIX DESIGN

 Test data for materials

DesignofM25(5%ofmicrosilica)

1. Cementused–PPC53grade

Specificgravityofcement–3.15

2. Microsilica–mineraladmixture

3. Specificgravityofmicrosilica–2.26

4. Chemicaladmixture–Superplasticizer

5. Specificgravityof

1. coarseaggregate–2.76

2. fineaggregate–2.69

3. chemicaladmixture–1.2

6. Degreeofsupervision–Good

7. Sieveanalysis- Zone

 Target strength for mix proportion

F’ck=fck+1.65SO

F’ck=25+1.65*4……

(FromIS10262-2019table2)

F’ck=31.6N/sq.mm OR

F’ck=fck+1.65X

F’ck=25+1.65*5.5…….

(FromIS10262-2019table1)

F’ck=34.075N/sq.mm

Whicheverishigher

Therefore,F’ck=34.075N/sq.mm

 Selection of water cement ratio

FromIS456-2000table5

ForM25w/cratiois0.45

 Water content selection For20mmaggregate,

Maximumwatercontent=186Kg

(IS10262-2019,table4)

Increasing 3% water content for every 25mm slump

Watercontentfor75mmslump =186+3/100*186 =191.57kg/cu.m

Assuming 18% water reduction by adding chemicaladmixture =191.57*0.82 =157.0875Kg/cu.m

 Calculation of cement content

W/Cratio=0.45

Cementcontent=157.0875/0.45=349.08

Approximately,350Kg/cu.m

Adding micro silica @ 5% of cementitious material=350*5/100=17.5kg/cu.m

Cement=350-17.5=332.5kg/cu.m

Min. cementations material should be 320Kg/cu.m

332.5Kg/cu.m>320Kg/cu.m …….(Henceok)

Therefore,Cement=333Kg/cu.m

 Proportioning of volume of coarse aggregate and fine aggregate content

AccordingtoIS10262-2019table3

Volume of CA corresponding to 20mm size aggregate and FA of zone 2 and after applying correction

Volumeofcoarseaggregate=0.63

Volumeoffineaggregate=0.37

 Mix calculation

a) Volumeofconcrete=1cu.m

b) Volumeof entrappedair=0.01cu.m

c) Volume of cement = (Mass of cement/Specific gravity of cement) * (1/1000)

=(332.5/3.15)*(1/1000)

=0.1057cu.m

d) Volumeofmicrosilica =(Massofmicro silica/specific gravity of micro silica)*(1/1000)

=(17.5/2.26)*(1/1000)

=0.00774cu.m

e) Volume of water = (Mass of water/specific gravity of water)*(1/1000)

=(157.0875/1)*(1/1000)

=0.158cu.m

f) Volume of admixture (Mass of admixtureis1.2%ofcement)

= (Mass of admixture/specific gravity of admixture)*(1/1000)

=(4/1.25)*(1/1000)

=0.0032cu.m

g) Volumeofallinoneaggregate

={(a-b)-(c+d+e+f)}

= {(1-0.01)(0.1057+0.00774+0.158+0.0032)}

=0.71536cu.m

h) Massofcoarseaggregate

= g*voume of CA*specific gravity of CA *1000

=0.71536*0.63*2.76*1000

=1243.86Kg/cu.

i) Massoffineaggregate = g* volume of FA*Specific gravity of FA*1000

=0.71536*0.37*2.69*1000 =711.99Kg/cu.m

 After applying moisture content correction in water final mix proportion For 1cu.m

I. Cement=169Kg/cu.m

II. Fineaggregate=707.19Kg/cu.m

III. Coarseaggregate=1235.96Kg/cu.m

IV. Microsilica=17.5Kg/cu.m

V. Admixture=4Kg/cu.m

VI. Water=169.78Kg/cu.m

 In this way, similarly mix design for M25(10%,15%replacementofmicrosilica) M30(5%,10%,15%replacementofmicrosilica) M35(5%,10%,15% replacement of micro silica) ISDONE.

FOR M25 FOR M30 FOR M35

5.RESULTS

ThecompressivestrengthofconcreteforM25,M30and M35 grade was tested at 7 days, 14 days and 28 days curingperiod.Theresultsaregivenbelow.

6.CONCLUSION

The compressive strength of concrete is increased For M25, M30 and M35 grades of concrete when replacementof cement with micro silica is doneup to 15%furtheradditionofmicrosilicaresultedindecrease instrength.

Addition of micro silica helped in proper bonding of ingredients present in concrete due which voids in the concrete was less and dense concrete structure was achieved. The workability of concrete is also improved due to addition of silica fume in concrete

Partial replacement of cement with micro silica can be economical as it is a waste product of industry and thusitcanhelpin reduction of CO2 emission.

7.REFERENCES

1. Concrete Technology Theory and Practice, M. S. Shetty, S. Chand Publication, Revised edition 2008.

2. Concrete Technology, M.L. Gambhir, McGraw Hill Education (India) Private Limited, 5th edition,2013.

3. IS 456-2000 : Plain and Reinforced Concrete –Code of Practice. Bureau of Indian Standard(FourthRevision).

4. IS 383-1970 : Specification for Coarse and Fine Aggregate from Natural Sources for Concrete(SecondRevision)

5. IS 10262 : 2019 – Concrete Mix Proportioning - Guidelines(SecondRevision).

6. Research paper on ‘Partial Replacement of CementBySilicaFume’ByRohitSharma.

7. Research paper on ‘Partial replacement of cement with silica fume and its effects on concreteproperties’.