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PERFORMANCE CHARACTERISTICS OFBLENDED CEMENT

Abstract : . Recent developments in civil engineering,such as high-rise buildings and long-span bridges, higher compressive strengthconcrete was the need of time. Currently, high-performance concrete is used in massive volumes due to its technical and economicadvantages. This study focuses on the strength performance of concrete with metakaolin, silica fume and its blend.Cementreplacements by 5%, 10%, 15%, 20% with metakaolin, silica fume and its blend are studied. Concrete tests are conducted on theconcrete samples at the specific ages. The comparison is made on the compressive strength performance of metakaolin, silica fumeconcrete and also its durability to acid resistance is studied.Keywords: Blended cement, silica fume, metakaolin, compressive strength, durability

I. INTRODUCTIONConcrete is a widely used construction material around theworld, and its properties have been undergoing changesthrough technological advancement. Numerous types ofconcrete have been developed to enhance the different

properties of concrete. With a fast population growth and ahigher demand for housing and infrastructure, accompanied

by recent developments in civil engineering, such as high-rise buildings and long-span bridges, higher compressivestrength concrete was the need of time. High performanceconcrete was proposed and widely studied at the end of thelast century. Currently, high-performance concrete is usedin massive volumes due to its technical and economicadvantages. Such materials are characterized by improvedmechanical and durability properties resulting from the useof chemical and mineral admixtures as well as specialized

production processes. Pozzolanic additives are thematerials or admixtures that canimprove concrete

properties such as concrete strength, durability andimpermeability. They are used either as partial substitutesof Portland cement or as an addition . The main componentof pozzolanic additives is usually active SiO2 in theamorphous phase. Pozzolanic reaction is a simple acid-

based reaction between calcium hydroxide (Ca(OH)2) andsilicium acid (H4SiO4) .The current pozzolans in use aresuch as fly ash, silica fume and slag. Development andinvestigation of other sources of pozzolan such as kaolin

will be able to provide more alternatives for the engineer toselect the most suitable cement replacement material fordifferent environments. This study focuses on the strength

performance of concrete with metakaolin, silica fume andits blend. Strength is the most important property ofconcrete since the first consideration in structural design isthat the structural elements must be capable of carrying theimposed loads. Strength characteristic is also important

because it is related to several other important propertieswhich are more difficult to measure directly. With regard tothis matter, the development of compression strength ofmetakaolin, silica fume and its blend concrete is studied.Cement replacements by 5%, 10%, 15%, 20% with

metakaolin, silica fume and its blend are studied. Concretetests are conducted on the concrete samples at the specificages. All the strength tests are limited to the ages of 28d

II. CEMENT REPLACING MATERIALS USED FORINVESTIGATION

1. Silica Fume :

Fig. 1. Silica fume powder

Silica fume, also referred to as microsilica or condensedsilica fume, is a byproduct material that is used as a

pozzolan This byproduct is a result of the reduction of high-purity quartz with coal in an electric arc furnace in themanufacture of silicon or ferrosilicon alloy. Silica fumerises as an oxidized vapor from the 2000°C (3630°F)furnaces. When it cools it condenses and is collected inhuge cloth bags. The condensed silica fume is then

processed to remove impurities and to control particle size.Condensed silica fume is essentially silicon dioxide(usually more than 85%) in noncrystalline (amorphorous)form. Since it is an airborne material like fly ash, it has a

spherical shape. It is extremely fine with particles less than1 μm in diameter and with an average diameter of about 0.1μm, about 100 times smaller than average cement particles.The relative density of silica fume is generally in the rangeof 2.20 to 2.5. Portland cement has a relative density ofabout 3.15. The bulk density (uncompacted unit weight) ofsilica fume varies from 130 to 430 kg/m3 (8 to 27lb/ft3).Silica fume is sold in powder form but is morecommonly available in a liquid. Silica fume is used inamounts between 5% and 10% by mass of the totalcementitious material. It is used in applications where ahigh degree of impermeability is needed and in highstrength concrete. With the addition of silica fume, the

slump loss with time is proportionally increased in concretemix. Due to the high surface area of silica fume particles inthe concrete mix, workability and consistency of concrete



2.1.1. Effect of silica fume on strength, on chemical, ondurability :Increase in compressive strength by using silica fume alsoresults an increase in the tensile and flexural strength.Increased tensile strength causes a possible reduction inslab thickness while maintaining high compressivestrengths. Hence, it reduces the overall slab weight and cost. Research has shown that addition of silica fume decreasesefflorescence due to the refined pore structure andincreased consumption of the calcium hydroxide. Theaddition of untreated silica fume to steel reinforcedconcrete enhances the corrosion resistance of thereinforcing steel. Silica fume decreases bleedingsignificantly. The durability of silica fume concrete tofreeze thaw is normally satisfactory at silica fume contentof less than 20%. The addition of silica fume to mortarenhances the freeze-thaw durability in spite of the poor airvoid system. The permeability of chloride ions in concretereduces by the addition of untreated silica fume.

2. Metakaolin :

Fig 2. Raw kaoliniteKaolinite is the clay minerals which provide the plasticity

of the raw material and change during firing to produce a permanent material. Kaolin is a phyllosilicate, consisting ofalternate layers of silica and alumina in tetrahedral andoctahedral coordination. Kaolinite is the mineralogical termfor hydrated aluminum disilicate, Al2Si2O5(OH)4, the

primary constituent of kaolin (40-70%). Other mineralscomprising kaolin include quartz, muscovite-like micas,and rutile.

Fig.3 Atomic arrangements of (a) Si 2O5 and (b) AlO(OH) 2

Metakaolin is usually produced by thermal treatment, i.e. ,calcination of kaolin clays within a definite temperaturerange. The main process important for production high

reactivity pozzolana from kaolin clay is calcination. Theheating process drives off water from the mineral kaolinite(Al2O3 2SiO2 2H2O), the main constituent of kaolin

The process is known as dehydroxylation , and is presented by simple equation:

Al 2O 3 2SiO 2 2 2O 3 2SiO 2 + 2H 2O↑ (1) 2.2.1. Effect of metakaolin on workability

Workability of concrete decreases as percentage ofmetakaolin or silica fume increases from 5% to 11% atintervals of 2% by replacement in OPC .By adding 10 %activated flyash in both the mixes of silica fume andmetakaoline workability is improved.

2.2.2. Effect of metakaolin on strength:Calcium hydroxide accounts for up to 25% of the hydratedPortland cement, and calcium hydroxide does notcontribute to the concrete’s strength or durability.Metakaolin combines with the calcium hydroxide to

produce additional cementing compounds, the materialresponsible for holding concrete together. Less calciumhydroxide and more cementing compounds means strongerconcrete. Metakaolin, because it is very fine and highlyreactive, gives fresh concrete a creamy, nonsticky texturethat makes finishing easier. Metakaolin aggressivelyconsumes calcium hydroxide.

III. Tests and Experimental Work done :Other than the two pozzolanic materials the materials usedwere ,Cement , Aggregates – fine and coarse, Water as per themix designTests on each of the above materials are conducted andthere results are as given ,3.1. Tests on Cement:1.Fineness test2.Standard Consistency3.Initial and Final setting time

Table.1.Physical Characteristics of CementSr.no Property Result Permissible

limit as perIS:12269

1. Normalconsistency

36 % -----------

2. Initial settingtime

200min >30 min

3. Final setting time 500min < 600 min4. Fineness

modulus98% passesthrough 90

micronsieve

----------

Ordinary Portland cement of 53 grade conforming to IS:12269 – 1987 being used for the experimentalinvestigation.The specific gravity of cement is 3.10

3.2. Tests on Aggregates:1.Aggregate impact value2.Aggregate Crushing Value3.Shape Test4.Specific Gravity5.Moisture content of aggregates6.Los Angeles Abrasion Value

Table.2.Physical property of fine aggregate, coarse aggregateSr.no Property Fine

AggregateCoarseAggregate



Modulus than 4.75mm 20mm2 Specific

Gravity2.50 2.68

3 CrushingValue

NA 16.5

4 Impact Value NA 5.65 Abrasion

Value NA 23.16

Table.3.showing the physical and chemical characteristics of materialsused

Physical property OPC SILICAFUME

METAKAOLIN

Specific gravity 3.1 2.2 2.54Mean grain size (μm) 22.5 0.15 2.54Specific area cm2/gm 3250 150000-

300000150000-180000

Colour greyish White Pinkish

Chemical property OPC SILICAFUME

METAKAOLIN

Silicon dioxide (SiO2) 20.25 85 60-65Calcium oxide (CaO) 63.61 0.2-0.8 0.2-0.8

Magnesium oxide(MgO)

4.56 0.2-0.8 0.2-0.8

Sodium oxide (Na2O) 0.08 0.5-1.2 0.5-1.2Potassium oxide(K2O)

0.51

Loss on ignition 3.12 <6.0 <1.4

In this study, the early age properties of fresh concrete andmechanical performance and durability of hardenedconcrete were examined. All tests were conducted using thefollowing sample groups:(1) an ordinary cement paste or concrete,(2) pastes or concrete substituted with 10% MK by mass.(3) pastes or concrete substituted with 10% silica fume by

mass.(4) pastes or concrete substituted with 5% silica fume bymass and 5% MK by mass,(5) pastes or concrete substituted with 5% silica fume bymass and 10% MK by mass,(6) pastes or concrete substituted with 5% silica fume by

mass and 15 % MK by mass(7) pastes or concrete substituted with 5% silica fume bymass and 20 % MK by mass

IV. RESULT AND DISCUSSION:Results of fresh and hardened concrete with partialreplacement of silica fume and metakaolin in combinationare discussed in comparison with those of normal concrete.For the above combinations of concrete mixes three cubes

were being casted each for varying curing days of 3,7,28days. Tests for the same being conducted undercompressive testing machine of capacity 2000KN

The following table shows the compressive as well as thetensile strength of the cubes casted .

Replacementlevels(%)

Compressive Strength (MPa) SplitTensiletest resultsSilica

fumeMetakaolin 3 days 7 days 28 days

0 0 30.885 36.775 42.33 4.1570 10 29.77 32.67 41.56 3.28910 0 29.64 32.11 39.11 4.675 5 26.97 31.20 46.22 2.55

5 20 26.03 33.46 41.67 3.67

Fig.4.Effect on compressive strength as per curing days onvarious % of cement replacement

4.1 Experimental Investigation for Durability conceptsregarding Acid Attack on Concrete:

The materials used for this purpose is as listed above in andtested as per the code provisions made in the above clauses. Even the mixes and mix proportion made according to therequirement is also mentioned in the above clause . BIScode procedure as per IS: 10262-1982 was followed forfinding the mix proportions of all the concrete specimens.Water binder ratio was considered as 0.4 to the optimum.

Testing methods for durability assessment :

a. Mass lossShowing the effect of acid solution on concrete byloss of mass

Mix Designation ConcreteGrade

Weightof

Concrete blocks beforeimmersi

on inacid

solution(kg)

Weight ofConcrete blocksafter 30

daysimmersion

in acidsolution

(kg)

Loss ofmass ofconcrete

due toacidic

reaction(%)

OPC M40 8.750 8.130 7.085

0PC+10%MK M40 8.560 8.180 4.439

0PC+10%SF M40 8.600 8.230 4.302

5%SF+5%MK M40 8.550 8.195 4.152

5%SF+10%MK M40 8.500 8.200 3.529

5%SF+15%MK M40 8.650 8.310 3.931

5%SF+20%MK M40 8.560 8.180 4.439

The OPC mix suffered the most deterioration interms of mass loss when immersed in 5% HClsolutions. The mass loss at 30 days cured M40grade PCC specimens was 7.085%. reaches the10% loss level within two weeks of immersion

period in 5% H2SO4. During the curing period,

level of mass loss increases and it shows that thehydration process of cementitious materials wasnot fully completed within 28 days curing.

0

10

20

30

40

50

60

0&0 0&10 10&0 5&5 5&10 5&15 5&20

c o m p r e s s i v e s t r e n g t h

( M P a )

Replacement of cement by SF and MK (%)



losses considerably. The mass loss of specimenswas approximately reduces 30% – 40% mass lossof PCC when immersed in 5% HCl solutions. Theminimum mass loss was observed in5%SF+10%MK concrete only. The M40 gradespecimens were shown only less than 10% massloss within the observation period of 4 weeks.

The results show that the resistance against theacid attack increased when cement replaced by SFand MK and the main reason for the increasedacid resistance of blended concrete investigatedwas the formation of dense hardened cement pasteand aggregate interface with low porosities.

The formation of unstable ettringite causes theconcrete matrix to be more porous and susceptibleto the acid attack through the capillary pores .

b. Strength deterioration factor (SDF)Showing the effect of acid solution on concrete bystrength loss

MixDesignation

ConcreteGrade

28 dayscompressivestrength onnormalcuring(N/mm 2)(f cw)

Compressivestrength ofconcrete cubesimmersed inacidic solutionof 5% HCl(N/mm 2) (f ca)

Loss ofstrengthofconcretedue toacidicreaction(%)

OPC M40 42.33 32.44 23.36

0PC 10% M40 41 56 35 78 13 90

0PC+10%SF

M40 39.11 35.12 10.20

5%SF+5%MK

M40 46.22 36.44 21.16

5%SF+10%MK

M40 47.56 44.00 7.48

5%SF+15%MK

M40 52.11 44.00 15.56

5%SF+20%MK

M40 41.67 33.78 18.93

The reduction of compressive strength due to acidattack was expressed in the form of strengthdeterioration factor (SDF). Figures above showthe SDF at30 days cured specimens of M40 gradeconcrete immersed in 5% HCl solution.

The PCC specimens are severely affected the acidattack and hence the SDF values of PCCspecimens were more than 23%. The rate ofchange SDF for PCC specimen was observed asrapid change up to 4 weeks of immersion period.The SDF for 5%HCl were shown in figures above.

Meantime the minimum SDF value of 7.48% wasobserved in 28 days cured M40 grade concreteafter the immersion period of 4 weeks. Theaddition of SF and MK in concrete specimensconsumes Ca(OH)2 and develop the secondaryhydration products (C-S-H gel) which reduces themicro pores of concrete and makes dense concretemass.

The ternary blended concrete specimens are lessaffected than that of the binary and controlconcrete mixes immersed in 5% HCl solutions.The presence of SF offered the resistance against

permeability during early ages and the MK

contents prevents the entry of acidic solutionsduring the latter ages. The ternary blendedcombination increases the impermeability ofconcrete in the higher order and hence theobserved SDF values were very less than that ofthe other mixes.

OPC

0PC+10%MK

0PC+10%SF

5%SF+5%MK

5%SF+10%MK

5%SF+15%MK

5%SF+20%MK

Weight of Concrete

blocksbefore

immersionin acid

solution (kg)

8.88.68.68.68.58.78.6

Weight of Concrete

blocks after30 days

immersion

in acidsolution (kg)

8.18.28.28.28.28.38.2

7.87.9

88.18.28.38.4

8.58.68.78.8



V. CONCLUSION :

From the above shown graph and results it is clearthat on 3 days strength there is not much change inincrease or gaining of strength by PCC and othersupplementary replacements of cement .

But as per the conventional curing for 28 days it isseen that the optimum results are obtained atreplacement of cement by 5%SF and 15%MK byweight of cement as highest strength is beingobtained.

Regarding split tensile strength still PCC holds

good results but it is seen that at metakaolinreplacement tensile strength can be improved.

Silica fume being finer holds good results against permeability and had shown good consistencyresults.

The PCC specimens of M40 grade concrete wereseverely deteriorated after immersion in 5%HClsolutions up to 4 weeks.

The mass loss within the concrete was the

maximum for OPC condition where as moderatefor the binary and least for the ternary conditions.

Thus as the acid concentration was beingmaintained throughout the immersion period of 4weeks in HCl solution still it shows appropriatemass loss and strength deterioration.

Even during strength deterioration the mostdrastically affected was the OPC cubes where asthe least affected were the ternary cubes.

Thus it proves that when cement is blended withcertain pozzolanic materials it gives better results

against durability and is safer than the normalcement concrete .

References :

1. Mohammad Panjehpou, Abang Abdullah Abang Ali, RamazanDemirboga1 “ A review for characterization of silica fume andits effects on concrete properties ”.

2. M. Mazloom, A.A. Ramezanianpour, J.J. Brooks, “ Effect of silica fume on mechanical properties of high-strengthconcrete”.

3. Brooks JJ, Megat Johari MA ., “ Effect of metakaolin on creepand shrinkage of concrete ” . Cem Concr Comp

4. Bai J, Sabir BB, Wild S, Kinuthia J ., “Strength developmentin concrete incorporating PFA and metakaolin ”

5. J.M. Justice, L.H. Kennison, B.J. Mohr, S.L. Beckwith, L.E.McCormick, B. Wiggins, Z.Z. Zhang, and K.E. Kurti s“Comparison of Two Metakaolins and a Silica Fume Used asSupplementary Cementitious Materials ”

6. Chan YN, Luo X, Sun W ., “Compressive strength and pore structure of high performance concrete after exposed to hightemperature up to 800_C ”. Cem Concr .

7. H. Abdul Razak, H.S. Wong (200 4), “ Strength estimationmodel for high-strength concrete incorporating metakaolin and

silica fume”. 8. J.M. Justice, L.H. Kennison, B.J. Mohr, S.L. Beckwith, L.E.

McCormick, B. Wiggins, Z.Z. Zhang, and K.E. Kurti s“Comparison of Two Metakaolins and a Silica Fume Used asSupplementary Cementitious Materials ”

9. G Christodoulou , “A comparative study of the effects of Silica fume, metakaolin and pfa on the Air content of fresh concrete”

G Christodoulou , School of Technology, University ofGlamorgan, Pontypridd, CF37 1DL, UK

OPC

0PC+10%

MK

0PC+10%SF

5%SF+5%

MK

5%SF+10%

MK

5%SF+15%

MK

5%SF+20%

MK

28 dayscompressivestrength for

normally curedcubes

42.3341.5639.1146.2247.5652.1141.67

compressivestrength of

blocks cured inacidic solution

32.4435.7835.1236.44 44 44 33.78

0

10

20

30

40

50

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