FOLAGBADE, Samuel Olufemi / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.674-679674 | P a g eEffect of cement additions on the plastic density and workabilityof concreteFOLAGBADE, Samuel OlufemiDepartment of Building, Faculty of Environmental Design and Management, Obafemi Awolowo University, Ile-Ife, 0220005, Nigeria.ABSTRACTThis paper reports the effect of cementcombinations containing Portland cement, flyash, silica fume and metakaolin on the plasticdensity and workability of concrete. The resultsshow that cement additions would reduce theplastic densities of Portland cement concrete withincreasing content. However, while fly ash binarycement concretes had plastic densities less than2400 kN/m3, silica fume and metakaolin binarycement concretes had plastic densities equal to orgreater than 2400 kN/m3. However, at a totalreplacement level less than 55%, all the cementcombination concretes achieved plastic densitiesbetween 2350-2450 kN/m3. Since fly ash reducedsuperplasticiser dosage and silica fume andmetakaolin increased superplasticiser dosage, thesuperplasticiser dosages of the ternary cementconcretes reduced with increasing content of flyash. The cement additions improved the cohesionand stability of concrete. However, due to theirincreased surface area, concrete becomes stickyresulting in poor finish with increasing content ofsilica fume and metakaolin. Also, metakaolinconcretes had higher plastic densities andrequired higher superplasticiser dosage thansilica fume concretes at equal replacement level.Keywords: cement additions; cementcombinations; cohesion; finishability; plasticdensity; workability.1. IntroductionFor good quality of workmanship, freshproperties of concrete like plastic density andworkability are very relevant to contractors andconcrete suppliers. While the plastic density couldbe used to assess the extent of the early strength ofconcrete, the workability could be used to assess theease of handling and placing of concrete. Hence,these properties would assist in making appropriatedecisions on handling (transportation), placing(including choice of formwork), compacting andfinishing of concrete.Also, for improved performance ofconcrete consistent with cost and environmentalcompatibility, the use of cement combinationconcrete has been supported by cement and concretestandards like BS EN 197- 1, BS 8500 and BS EN206- 1. Due to its availability, low cost and qualitystandard, fly ash constitutes the primary pozzolanain blended cements. Despite its slow early ageperformance, it generally contributes to later-agestrength development and improvedresistance[3,4,5]. Also, its spherical shape[6,7] andthe electronic dispersion of its fine particles hasresulted in reduced water demand and improvedworkability of concrete. Silica fume andmetakaolin, due to their fineness, would generatemore nucleation sites to accelerate hydrationreactions[11,12,13] and enhance both early and laterage performance of concrete[14,15,16] but their fineparticle size and high reactivity would causeworkability problems[17,18,19, 20]. While BS EN197- 1 permits the use of fly ash of up 55%, silicafume and metakaolin because of their high costscould only be used, respectively, in small quantititesof about 5-10% and 5-15% by mass ofcement[21,22]. However, when combined, thesecement additions would compliment each other inconcrete performance.Hence, to support the use of cementcombinations within these permitted limits, thispaper investigated the effect of the binary andternary combinations of the cement additions on theplastic density and workability of concrete.2. Experimental materialsThe cements used were Portland cement(PC, 42.5 type) conforming to BS EN 197- 1,siliceous or Class F fly ash (FA) conforming to BSEN 450, silica fume (SF) in a slurry form (50:50solid/water ratio by weight) conforming to BS EN13263 and a calcined natural pozzolana (metakaolin,MK) conforming to BS EN 197- 1. The propertiesof the cements are presented in Table 1. Theaggregates consisted of 0/4mm fine aggregates and4/10mm and 10/20mm coarse aggregates. Thecoarse aggregates were uncrushed and they come invaried shapes. The 4/10mm aggregates have roughtexture and the 10/20mm aggregates were smooth.The properties of the aggregates are presented inTable 2.
FOLAGBADE, Samuel Olufemi / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.674-679675 | P a g eTable 1: Physical and chemical properties of cementsPROPERTYCEMENTSPC FA MK SFBlaine fineness, m2/kg 395 388 2588 *Loss on ignition, % a)1.9 6.1 b)0.9 2.7Particle density, g/cm33.17 2.26 2.51 2.17% retained by 45µm sieve b)- 11.0 - -Particle size distribution, cumulative % passing by mass c)125 µm 100 100 100 100100 µm 98.2 99.2 100 10075 µm 93.2 96.5 99.8 10045 µm 81.8 87.0 99.4 10025 µm 57.1 66.2 96.0 98.810 µm 30.1 40.6 76.2 93.85 µm 13.5 24.1 50.7 87.52 µm 5.6 10.9 18.2 85.51 µm 2.9 4.8 4.7 78.70.7 µm 1.3 1.9 1.4 50.70.5 µm 0.2 0.3 0.1 10.5* Fineness for SF = 15,000-30,000 m2/kga) In accordance with BS EN 196-2b) In accordance with EN 450- 1c) Obtained with the Laser Particle SizerThe concrete mix proportions, for the cementcombinations in Table 3, were based on the BREDesign Guide using a normal weight of 2400kN/m3and a free water content of 165 kg/m3toavoid excessively sticky mixes. Potable water(conforming to BS EN 1008) and a superplasticiser(conforming to EN 934-2) were used for mixingthe concretes. To provide a uniform basis forcomparing the superplasticiser dosages, concretewere produced to a consistence level of S2 (BS EN206- 1) defined by a nominal slump of 50-90 mm.Table 2: Physical properties of fine and coarse aggregatesPROPERTYFINE AGGREGATES 1)0/4 mmCOARSE AGGREGATES 1)4/10 mm 10/20 mmShape, visual - Varied VariedSurface texture, visual - Rough SmoothParticle density 2)2.6 2.6 2.6Water absorption, % 3)1.0 1.7 1.2% passing 600 µm sieve 55.0 - -1) Aggregates were obtained from Wormit Quarry.2) In accordance with BS EN 1097- 63) In accordance with BS EN 1097- 6, Laboratory-dry condition
FOLAGBADE, Samuel Olufemi / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.674-679676 | P a g e3. Experimental methodTo investigate the effect of cementcombinations on workability, the superplasticiserdosages and extent of cohesion or stability andfinishability of the concretes were assessed. Theslump test which could be used to determine thecapacity of concrete to hold water and coarseaggregates has been used to assess theworkability properties. The superplasticiserdosages for the cement combinations weredetermined at a consistence level of S2 defined bya nominal slump of 50-90 mm in BS EN 206- 1.Concrete was prepared to BS EN 12390- 2and slump test was carried out to BS EN 12350- 2.A dampened truncated cone (100mmФ x 200mmФx 300mm) placed on a horizontal base plate andheld firmly in position with the aid of the foot rests,was filled with fresh concrete placed in threelayers, each approximately one-third of the heightof the cone when compacted. Each layer wascompacted with 25 strokes of the tamping rod(16mmФ x 600mm) uniformly distributed over thecross-sections and depths of the layers. The toplayer was over-filled and the excess, after tamping,was removed by the sawing and rolling movementof the compacting rod. After this, the spilledconcrete was removed from the base plate and thecone was carefully lifted vertically and placedinverted next to the slumped concrete. Thedifference between the height of the mould and thehighest point of the slumped concrete was thenmeasured, to the nearest 5mm with the aid of aruler, as the slump and the quantities ofsuperplasticiser required at a consistence level ofS2 were obtained for the mixes. Cohesion andfinishability were visually assessed. Cohesion wasassessed by the extent of the firmness or loosenessof the slumped concrete when tamped many timeswith a rod. Finishability was assessed by thequality of finish.Plastic density test was determined to BSEN 12350- 6 using the concrete mixes at aconsistence level of S2. Concrete was compactedinto a rigid and water-tight container of knownvolume and mass and weighed to determine itsmass and hence its density. The container afterbeing calibrated to obtain its volume and weighedto obtain its mass, was filled with fresh concrete inthree layers to ensure the full compaction of theconcrete. The container with its content, at eachstage, was carefully compacted with the vibratingtable while being held firmly against the table. Thetop surface of the concrete was smoothened with asteel float and skimmed with a straight edge. Aftercleaning the outside surface of the container, thecontainer was weighed and the plastic density wascalculated by dividing the mass of the concretewith the volume of the concrete.4. Analysis and discussion of resultsTable 3 shows that plastic densitygenerally reduced with increasing water/cementratio and increasing total content of the cementadditions. Hence, compared with Portland cement,the addition of the cement additions reduced theplastic densities of concretes. However, while silicafume and metakaolin binary cement concretesachieved plastic densities greater than 2400 kN/m3,the plastic densities of the fly ash binary cementswere lower than 2400 kN/m3. While the plasticdensities of the ternary cement concretes werelower than 2400 kN/m3all the cement concretes ata total replacement level of less than 55% haveplastic densities within the range of 2350 and 2450kN/m3generally used for normal weight concrete.Metakaolin as a binary or ternary cementcomponent produced concretes with higher plasticdensities than silica fume at equal replacementlevel and this is probably due to its higher particledensity (Table 1).Table 3 shows that superplasticiser dosagereduced with increasing water/cement ratio. Whilefly ash, as a binary cement component, reducedsuperplasticiser dosage with increasing content,silica fume and metakaolin, as both binary andternary cement component, increasedsuperplasticiser dosage with increasing content atequal water/cement ratio. Also, the superplasticiserdosages of the ternary cement concretes reducedwith increasing content of fly ash. Metakaolinrequired higher superplasticiser dosage than silicafume at equal replacement level. As silica fume isfiner than metakaolin and should require highercontent of superplasticiser than metakaolin at equalwater/cement ratio, the higher superplasticiserdosages recorded for metakaolin concretes wouldtherefore be due to the fact that the effect ofangular shape of metakaolin supercedes the effectof the higher fineness of silica fume on waterrequirement.
FOLAGBADE, Samuel Olufemi / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.674-679677 | P a g eTable 3: Superplasticiser dosage and plastic density of concrete at a consistence class S2 in BS EN 206-1(defined by a nominal slump of 50-90 mm)MIX COMBINATIONSUPERPLASTICISER DOSAGE AND PLASTIC DENSITYOF CONCRETEw/c = 0.35 w/c = 0.50 w/c = 0.65SPa,%PDb,kN/m3SPa,%PDb,kN/m3SPa,%PDb,kN/m3100%PC 0.41 2420 0.33 2395 0.25 238580%PC+20%FA 0.37 2390 0.30 2375 0.23 236580%PC+15%FA+5%MK 0.43 2390 0.35 2375 0.26 237080%PC+15%FA+5%SF 0.40 2390 0.31 2375 0.24 236565%PC+35%FA 0.33 2370 0.27 2360 0.20 235565%PC+30%FA+5%MK 0.40 2370 0.35 2360 0.27 235565%PC+25%FA+10%MK 0.45 2375 0.39 2365 0.31 236065%PC+30%FA+5%SF 0.38 2365 0.29 2360 0.23 235565%PC+25%FA+10%SF 0.40 2365 0.35 2360 0.26 235545%PC+55%FA 0.31 2340 0.26 2340 0.19 234045%PC+45%FA+10%MK 0.38 2345 0.34 2345 0.27 234545%PC+40%FA+15%MK 0.41 2350 0.37 2345 0.28 234545%PC+45%FA+10%SF 0.36 2340 0.31 2340 0.24 234095%PC+5%MK 0.43 2415 0.35 2390 0.26 238090%PC+10%MK 0.47 2410 0.39 2390 0.29 238085%PC+15%MK 0.51 2405 0.43 2385 0.33 237595%PC+5%SF 0.43 2410 0.35 2390 0.26 238090%CEM I+10%SF 0.46 2400 0.38 2385 0.28 2375a) % Superplasticiser (SP) is related to the total cement content.b) Plastic density of concreteThe cohesion of the concrete mixes wasalso assessed as described earlier with the aid of theslumped concretes. Cohesion of concrete wasobserved to generally reduce with increasingwater/cement ratio. Compared with Portland cementconcrete, the use of cement additions was observedto result in improved cohesion and thereforestability of the concrete mixes at equal water/cementratio. This is probably due to improved particlepacking, improved viscosity or higher water neededby the fine materials (especially silica fume andmetakaolin). Compared with the FA binary cementconcrete, the higher fineness of silica fume andmetakaolin also resulted in ternary cement concretewith higher cohesion. However, increasing cohesionwas observed to have a negative effect onfinishability. This is because the higher thecohesion, the higher the stickiness and the difficultyin obtaining a smooth finish.5. ConclusionThe plastic density of concrete wouldreduce with increasing water/cement ratio and thereplacement of Portland cement with cement
FOLAGBADE, Samuel Olufemi / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.674-679678 | P a g eadditions would reduce the plastic densities ofconcretes with increasing content. While only thesilica fume and metakaolin binary cement concretesachieved plastic densities of 2400 kN/m3or more,only the ternary and fly ash binary cement concretesat a total replacement levels less than 55% achievedplastic densities of 2350 kN/m3or more. Also,metakaolin due to its higher particle densityproduced concretes with higher plastic densitiesthan silica fume at equal replacement level.Superplasticiser dosage reduced withincreasing water/cement ratio and while the additionof fly ash would reduce superplasticiser dosage, theaddition of silica fume and metakaolin as bothbinary and ternary cement component wouldincrease superplasticiser dosage with increasingcontent. Hence, the superplasticiser dosages of theternary cement concretes reduced with increasingcontent of fly ash. Metakaolin requires highersuperplasticiser dosage than silica fume at equalreplacement level probably because the effect of thefineness and angular shape of metakaolin particlessupersedes the effect of the higher fineness andspherical shape of silica fume particles on the waterrequirement of concrete.The cohesion of the concrete reduced withincreasing water/cement ratio and due to improvedparticle packing and higher viscosity, the use ofcement additions would improve the cohesion andstability of concrete. Also, silica fume andmetakaolin due to their higher fineness would resultin concrete with higher cohesion, stickiness andpoor finish than fly ash concrete.References Antiohos S. K., Papadakis V. G.,Chaniotakis E., Tsimas S., Improving theperformance of ternary blended cementsby mixing different types of fly ashes,Cement and Concrete Research, 37 (6),2007, 877-885. Lam L., Wong Y. L., Poon C. S., Effect offly ash and silica fume on compressive andfracture behaviours of concrete, Cementand Concrete Research, 28 (2), 1998, 271-283. Naik T. R., Singh S., Ramme B.,Mechanical properties and durability ofconcrete made with blended fly ash, ACIMaterial Journal, 95 (4), 1998, 454-462. Dhir R. K., Jones M. R., Development ofchloride-resisting concrete using fly ash,Fuel, 78 (2), 1999, 137-142. Papadakis V. G., Effect of supplementarycementing materials on concrete resistanceagainst carbonation and chloride ingress,Cement and Concrete Research, 30 (2),2000, 291-299. Concrete Society, The use of GGBS andPFA in concrete: Technical Report No 40(The Concrete Society, London, 1991). Mindess, S., Young, F. J. and Darwin, D.,Concrete (Prentice-Hall, 2003). Helmuth, R., Fly ash in cement andconcrete (Portland Cement Association,Skokie, Illinois, 1987). Dhir R. K., McCarthy M. J. and Paine K.A., Use of fly ash to BS EN 450 instructural concrete (Thomas Telford,2002). Thomas M. D. A., Shehata M. H.,Shashiprakash S. G., Hopkins D. S. andCail K., Use of ternary cementitioussystems containing silica fume and fly ashin concrete, Cement and ConcreteResearch, 29 (8), 1999, 1207-1214. Mehta, P, K. and Aitcin P. C., Principlesunderlying production of high-performanceconcrete, Cement, Concrete andAggregates, 12, 1990, 70-78. Langan B. W., Weng K. and Ward M. A.,Effect of silica fume and fly ash on heat ofhydration of Portland cement, Cement andConcrete Research, 32 (7), 2002, 1045-1051. Bai J. and Wild S., Investigation of thetemperature change and heat evolution ofmortar incorporating PFA and metakaolin,Cement and Concrete Composite, 24 (2),2002, 201-209. Shehata M. H. and Thomas M. D. A., Useof ternary blends containing silica fumeand fly ash to suppress expansion due toalkali-silica reaction in concrete, Cementand Concrete Research, 32 (3), 2002, 341-349. Wild S., Khatib J. M., Jones A., Relativestrength pozzolanic activity and cementhydration in superplasticised metakaolinconcrete, Cement and Concrete Research,26 (10), 1996, 1537-1544. Bai J., Sabir B. B., Wild S. and Kinuthia J.M., Strength development in concreteincorporating PFA and metakaolin,Magazine of Concrete Research, 52 (3),2000, 153-162. Bai J., Wild S., Sabir B. B. and Kinuthia J.M., Workability of concrete incorporatingpulverized fuel ash and metakaolin,Magazine of Concrete Research, 51 (3),1999, 207-216. Bouzoubaa N., Bilodeau A., SivasundaramV., Fournier B and Golden D. M.,Development of ternary blends for highperformance concrete, ACI MaterialJournal, 101 (1), 2004, 19-29. Park C. K., Noh M. H. and Park T. H.,Rheological properties of cementitious
FOLAGBADE, Samuel Olufemi / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.674-679679 | P a g ematerials containing mineral admixtures,Cement and Concrete Research, 35 (5),2005, 842-849. Wong H. S. and Abdul Razak, H.,Efficiency of calcined kaolin and silicafume as cement replacement material forstrength performance, Cement andConcrete Research, 35 (4), 2005, 696-702. Dunster A., Silica fume in concrete:Technical Information Paper 5/09 (BRE,2009). Advanced Cement Technologies, availableatwww.advancedcementtechnologies.com(accessed 10 April 2013). Holland, T. C., Silica Fume User’sManual: Technical report (Silica FumeAssociation, Lovettsville, VA 22180, USA,2005). Teychenne D. C., Franklin R. E. andErntroy H. C., Design of normal concretemixes, 2ndEd., amended by B. K. Marsh(Building Research Establishment, 1997). Metha P. K. and Monteiro P., Concrete:Microstructure, properties and materials(McGraw Hill, 1997).