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29th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 25 - 26 August 2004, Singapore

EFFECT OF BLENDING OF PORTLAND CEMENT WITH GROUND GRANULATED BLAST FURNACE SLAG ON THE PROPERTIES OF CONCRETE

Kamran Muzaffar Khan*, University of Engineering &Technology Taxila, Pakistan Usman Ghani, University of Engineering & Technology Taxila, Pakistan

ABSTRACTPortland cement, already being a very expensive material constitutes asubstantial part of the total construction cost of any project and the situation has furtherbeen aggravated by the energy crisis, which has further increased the cost ofproduction of Portland cement. Therefore, it is of current importance for the country toexplore and develop cementing materials cheaper than Portland cement. In thisresearch, GGBS (Ground Granulated Blast furnace Slag) was collected from Steel MillsKarachi (Pakistan) and pulverized to a very fine degree from a pulverizer. Physicall

Chemical properties, such as, compressive strength, fineness, setting times, soundnessand chemical composition of GGBS (Ground Granulated Blast furnace Slag) wereinvestigated and comparison has been made with the relevant properties of cementEffect of replacement was seen on workability, compressive strength, tensile strength,modulus of rupture, equivalent cube strength by casting mixes of different ratios;1 2:4,1 :1.5:3,1 :1.25:2.50, 1:1 :2. WIC ratio for first two mixes was kept as 0.65 and forrest two mixes as 0.45.After cost comparison of GGBS and Ordinary Portland Cement itis concluded that p rice of G GBS is 25% to 50% less than that of Ordinary PortlandCement. This aspect of GGBS makes it economical.Key words. GGBS, Cement replacement materials, concrete

1. IntroductionConsidering the high prices of Portland cement, a considerable need in our Pakistan forpromoting cementitious materials cheaper than ordinary Portland cement. Planners, economists andscientists are keenly alive to the need of materials to meet the ever-increasing demand and very highprices of Portland cement. Another outstanding feature of GGBS is its resistance to alkali aggregate reactions .Cement replacement materials can partially replace Portland cement to some extent. ForPakistan the development of cement replacement materials as substitute of cement is of currentimportance as the country has large irrigation, highway networks and building programmes and big plansfor their expansion in the near future.It is to present that the finely ground GGBS can be used as a partial substitute of Portlandcement to make concrete with satisfactory material properties similar to that shown by normal concrete.The research work overall aimed at to compare the different properties of fresh & hardened concrete

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made with different cement replacement levels of GGBS, with concrete having pure OPC (OrdinaryPortland cement).Following properties of concrete using pure cement and blended cements with GGBS weretested and compared1. Workability2. Compo Strength

3. Tensile strength4. Modulus of rupture.2. Literature Review2.1 Workability. P.J.Wainwright reported that for concretes made with equal slump, lower water content isrequired compared to O.P.C. [9] The report given by ACI describes the presence of GGBS in the miximproves workability and makes the mix more mobile but cohesive. [2]2.2 Compressive. StrengthIf a slag cement concrete and an OPC concrete are designed to have the same 28-day strength,the slag cement concrete will require higher cement content. At one year, however, the slag concrete willhave achieved a significantly higher strength than the Portland cement concrete.[1]2.3 Tensile StrengthThe development of tensile strength of slag cement concretes is similar to that of compressivestrength and is influenced by the same factors (i.e. temperature, humidity, replacement level, compositionof slag and cement). When comparisons are made on the basis of equal compressive strengths thenslag cement concretes have a higher tensile strength than Portland cement concrete. [1]2.4 Modulus of ElasticityThe rate of gain of modulus at early ages for slag cements increases far more with an increase intemperature than an equivalent Portland cement concrete [1]3. Properties of GGBS3.1 Chemical Composition of GGBSOxide composition of GGBS was found using X-ray Diffraction Machine with the cooperation ofBestWay Cement Pakistan GGBS contains 36.53% CaO, 31.54% Si02 , 13.03% A1 20 3, 8.68% MgO,1.13% S033.2 FinenessFineness in terms of specific surface area was found in lab using Blain's Air permeabilityapparatus as 3800cm2/gm.4. Testing of concrete. Four mixes namely 1 2:4, 1:1 :5:3, 1: 1.25:2.50& 1.1:2 at three different replacement levels of cement i.e., 0%, 25%, 50% by GGBS were made and tested. Various properties of concrete (fresh and hardened) have been investigated in this research work. Their results are represented in the table 1. 5. Discussion5.1 Workability of ConcreteThe workability for various mixes, for specified replacement levels of Portland cement by finelyground GGBS, maintaining a constant water cement ratio was measured by slump test.As evident from the results of Table (1) and graph-1, there was an appreciable increase in theworkability of concrete with increaSing the percent replacement of cement by GGBS. Also duringmoulding of test specimens and handling of GGBS mixed concrete reflected the plasticizing effect of fineparticles in increasing the mobility of the aggregate in the concrete.Also replacement by weight resulted in a considerably greater volume of the cementitiousmaterial due to substantial difference in the specific gravitates of cement (3.10) and finely ground GGBS(2.90). Therefore, GGBS was more plastic, having an improved finishibility and easier placing.

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5.2 Compressive Strength of ConcreteFrom the examination of the compressive strength test results on different concrete mix ratios (1 :2: 4, 1 1.5:3, 1 1.25:2.50, 1:1 :2) by varying the % replacement of cement with GGBS (0%, 25% & 50%),following observations are made.1) There was a decrease in early age strength i.e. 3 day and 7 day, as the replacement level wasgradually increased from 25 percent 50 percent. Whereas there was an appreciable gain in strength after7 days up to 28 days, as GGBS mixed concrete giving almost same strength as that of the plain cementconcrete. However, mixes with 50 percent replacement level have yielded slightly lowest strengths2. Compressive strength decreases as the % replacement of cement is increased but the % reduction instrength is different at different ages of concrete . I.e. more % reduction in 3 days strength and lesser in28-day's strength.3) Another important thing which was observed that % strength reduction was more in case of 1 2:4 mixratio than 1 1.5:3 and % strength reduction was more in case of mix ratio 1 1.25:2.50 than 1:1 2.Minimum % strength reduction was in case of mix ratio 1:1:2 and maximum in case of 1 2:4. It meansthat with the increase in the cement quantity, the strength reduction can be minimized4) A more important thing which was observed that if water cement ratio is decreased using waterreducers, % strength reduction can be minimized in addition to the other benefit of using GGBS as partialreplacer of cement.Graphically results are represented in graph (2,3,4,5).5.3 Tensile Strength of ConcreteThe results of splitting tensile strength for plain and GGBS mixed on concrete of the fourtraditional mixes are shown in the following tables &graphs.It is evident from the splitting tensile strength test results that in al/ the four mixes, effect ofdecrease in the early age strength due to replacement of cement by GGBS is less pronounced ascompared to compressive strength. Further more there is no substantial decrease in 28 day splittingtensile strength even up to 50 percent replacement levels. Up to 25 percent replacement the GGBSmixed concrete is yielding almost the same splitting tensile strength as that of plain cement concrete .Graphically results are represented in graph (6).5.4 Modulus of Rupture of ConcreteBehaviour of Modulus of rupture Of Concrete is found to be quite different from that ofcompressive strength. Rate of % reduction in flexural strength is low as replacement levels increasesGraphically results are represented in graph (7).6. ConclusionsAs there was an appreciable increase in the workability of concrete with increasing percentreplacement of cement with ggbs, therefore wlc ratio can be reduced keeping the slump constant, whichwill result in an increase in compressive strength. Even if wlc ratio is decreased using water reducers,compressive strength can be increased up to strength of normal cement concrete.

Effect of partial replacement was very small tensile strength and modulus of rupture .i.e, betweenstrength of control mix & the blended cement concrete. GGBS is a waste product and only grindingmakes it fit for use. so it very economical cement replacement material. Consequently it also reduces thecost of concrete. Using ggbs as cement replacement material is a suitable way for its disposal, so thistechnique is environment friendly.

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Table .1 RESULTS OF CONCRETE TESTING MixRatio W/CRatio WaterContent(Kg/m3)

%ReplacementSlump(mm) Compressive Strength (psi) TensileStrength(psi)

Modulus ofRupture(psi)EquivalentCube Strength(psi)

3 Days 7 Days 28Days1:2:4 0.65 204 0 25 2310 2966 4101 380 639 394325 45 1686 2467 3789 368 639 360750 65 1062 1592 2810 344 581 30001:1.5:3 0.65 260 0 126 2435 3422 4682 418 710 4800

25 Collapse 2000 3060 4247 400 681 443450 Collapse 1405 2185 3528 368 649 35001 1.25 :2.50 0.45 208 0 65 3795 3997 5777 515 897 549925 87 2623 3778 5152 489 865 500850 103 2092 3029 4715 423 810 45031:1 :2 0.45 247 0 86 4340 5589 6339 563 981 624525 100 3029 4997 6058 500 978 587350 120 2536 4247 5277 461 963 4978

Graph (1) Relation b/w Workability & % Cement Replacement --------- - - - ----,

Workability of Concrte

200 r-:-..---- .. ....I ---+-1 :02 :04- ,150 ~ 0 - - v - 1 :1 .25 :2.50, 100 ~ : : : : : : : : ~ ~ = = = = : : ~t ;'f """*'-1 :01 :025 0 ~ ~ ____- - - - ~ ~ - - - - - - - - ~ J __ __ ~ - - - - - - ~ - - __ - - ~

0% 20% 40% 60% % Cement Rlplacement

Graph (2)Relation b/w Compressive Strength & % Cement Replacement

Compressive Strength of 1:2:4 Concrete at w/c=O.65I -30ays 1 li 5000 __ 7 Days ,!c 4000 o-- - - - - . lL --t:r- 28 Days i_ J

.1 f 3000r - - - ______: .!: 2000 r - - - - ~ ~ . : : : : : : : : ! a 1000 I

O + - - - - - - - ~ - - - - - - - r - - - - - - ~ COAl 20% 40% 60%

%Cement Replacement

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I


Compressive St,rength of 1:1.5:3 Concrete atw/c=O.65

I-+ - 3 Days 15000 lr - - - " - ( l _ ~ j-4-7 Days4000 L 28 DaysJ3000r---_ __m eeIl_ 2000r----....- __ - = ~ ell..CIl 1000oEoo O + - - - - - - - ~ - - - - - - - - ~ - - - - - - ~ 0% 20% 40% 60%

%Cement Replacement


Compressive Strength of 1:1.25:2.50Concrete atwlc=O.45 - - - .-+-3 Days7000 _ __ 7 Days

6000 IDc=' 5000 i - - - - f r -____ . . / \ y .-> '"1.eIl_ 1II.cD _ 4 0 0 0 : : : : : = - .....--_ _.. 01C1. c 3000ECI l 2000..ot i ; 1000O + - - - - - - - ~ - - - - ~ ~ - - - - ~ 0% 20% 40% 60%

%Cement Rsplacement


Compressive Strength of 1:1;2 Concrete at w/c=O,45

l.ea, 7500cI 6000 ~ = = = - - ~ r - - - ___A~ o o l : ~ - - - - ~ ~ - ~ : : : : ~ > II )'iii ~ o o o II) II l i 1500I E, 0 o + - - - - - - - - - ~ - - - - - - - - ~ - - - - - - ~1 0% 20% 40% 60%

%C .ement Re.placementL _ _

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Graph (6) Relation b/w Tensile Strength & % Cement Replacement

Tensile Strength of Concrte

- 600.. ioo. -+- 1 02-:04--15 0 0 4 ~ = = = = = = = - - ! p . = = = = = = = = ~ _ _ _ 01:1 .5:3.0 II4 o o ~ I L ~ = = = = = = = = ~ - = = = = = = = = ~ ~ ! 300. "P ' L 0 - 1 :1.25 :2.50 I; -M-1 :01 :02200:! 100~ O + - - - - - - - - r - - - - - - - - ~ - - - - - - _

0% 20% 40% 60% % Cement Replacement

Graph (7) Relation b/w Modulous of rupture & % Cement Replacement - - - - -- - - _._------ --

Modulous of ~ p t u r e of Concrte

: ; 1200....... 1:02:04.. 1000: I _ _ _ 01:1 .5:3.0-- 800 - 0 - 1 :1.25 :2.50 600

...0I. !0' a0:E400200

00% 20% 40%

-M-1 :01 :02

60%"10 Cement RBplacement

7.REFERENCES1 A. M. Neville Properties of Concrete, 4th Edition (2003).2 ACI226.1R-87, Ground Granulated Blast furnace Slag as a cementitious constituent in concrete,ACI Manual of concrete practice, part 1 Materials and general properties of concrete,16pp(Detroit Michigan, 1994)3 A. M. Neville Concrete Technology.4 F. M. Lie Chemistry of Cement.5 R.N.Swamy, Cement replacement materials (1986)6 BRITISH STANDARDS BS 6699:19927 ASTM C 989-948 Annual book of ASTM standards (1998).9 P.J.Wainwright. Blended Cements-The use of GGBS and PFA in Concrete.

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