Behaviour of self compacting concrete using Portland pozzolana cement with different levels of fly ash.pdf



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Technical Report Behaviour of self compacting concrete using Portland pozzolana cement with different levels of fly ash P Dinakar ⇑ , M Kartik Reddy, Mudit Sharma School of Infrastructure, Indian Institute of Technology, Bhubaneswar 751 013, India a r t i c l e i n f o Article history: Received 22 August 2012 Accepted 9 November 2012 Available online 23 November 2012 a b s t r a c t The influence of including fly ash (FA) on the properties of self-compacting concrete (SCC) is
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  Technical Report Behaviour of self compacting concrete using Portland pozzolana cement withdifferent levels of fly ash P Dinakar ⇑ , M Kartik Reddy, Mudit Sharma School of Infrastructure, Indian Institute of Technology, Bhubaneswar 751 013, India a r t i c l e i n f o  Article history: Received 22 August 2012Accepted 9 November 2012Available online 23 November 2012 a b s t r a c t The influence of including fly ash (FA) on the properties of self-compacting concrete (SCC) is investigatedPortland pozzolana cement (PPC) was partially replaced with 10–70% fly ash The water to binder ratiowas maintained constant at 030 for all mixes Properties included were self-compactibility properties(slump flow, V-funnel time and L-box blocking ratio) mechanical properties (compressive strength, split-ting tensile strength and elastic modulus), and durability properties (water absorption, water penetrationdepth and chloride permeability) The results indicate that fly ash along with PPC can be used in SCC toproduce high strength high performance concretes Replacing 30% of PPC with FA resulted in strength of nearly 100 MPa at 56 days Splitting tensile strength and elastic modulus values have also followed thesame trend High absorption values were obtained with increasing amount of FA, however, all the SCCsexhibited initial absorption values of less than 3% The water penetration depths in SCCs were lower at10% and 30% replacements of fly ash but remained higher at 50% and 70% replacements There is a sys-tematic reduction in the chloride permeability of SCCs at 30% replacement of fly ash   2012 Elsevier Ltd All rights reserved 1 Introduction Self Compacting Concretes (SCCs) require high flowabilitythrough a superplasticiser, and to remain cohesive during handlingoperations special attention is needed in terms of the sand andpaste content apart from a viscosity-modifying admixture to en-hance stability [1] It is well established earlier that the use of min-eral admixtures such as fly ash and blast furnace slag couldincrease the slump of the concrete mixture without increasing itscost, while reducing the dosage of superplasticiser needed to ob-tain similar slump flow compared to concrete made with Portlandcement only [2] Also, the use of fly ash improves rheological prop-erties and reduces the cracking potential of concrete as it lowersthe heat of hydration of the cement [3] It was proved from earlierstudies that up to replacement of 30% fly ash results in a significantimprovement of the rheological properties of flowing concretes[4,5] The use of fly ash reduces the demand for cement, fine fillersand sand [6], which are required in high quantities in SCC More-over, the incorporation of fly ash also reduces the need for viscos-ity-enhancing chemical admixtures [7]High-volume fly ash (HVFA) concretes at about 60% cementreplacement have been reported to achieve excellent mechanicaland durability properties [8] There are no studies reported onthe production of SCC when PPC was used with additional replace-ment of fly ash Bouzoubaa and Lachemi [9] reported on the pro-duction of HVFA–SCC that was flowable, cohesive, and developeda 28-day compressive strength of about 35 MPa Researchers alsoattempted to produce high-volume fly ash SCCs by replacing upto 70% of Portland cement with class F fly ash [10–12] Coal bottomash has also been successfully used as sand replacement in thedevelopment of self compacting concrete [13] Fly ash in high vol-umesinSCCs also improvedthe durabilityand corrosionpropertiesstudied [10,11,14] In order to extend the general concept of HVFAconcreteand its applications to a widerrange of infrastructure con-struction, this paper outlines the results of a research projectaimed at producing and evaluating the behavoiur of SCCs incorpo-rating high volumes of class F fly ash when Portland pozzolanacement (PPC) was used 2 Research significance The approach of manufacturing of SCC was recently modifiedand developed to produce SCC with high performance and high-strength characteristics [15–17] However, all previous effortsand attempts in the field of SCC were concerned with OrdinaryPortland cement (OPC) and mineral blends such as fly ash, slagand limestone powder, there is a lack of knowledge regarding theutilisation of Portland pozzolana cement (PPC) with mineral blendsin the development of SCC Generally, there is a great interest andtendency between researchers and concrete technologists to 0261-3069/ - see front matter    2012 Elsevier Ltd All rights reservedhttp://dxdoiorg/101016/jmatdes201211015 ⇑ Corresponding author Tel: +91 674 2306353 E-mail addresses:  pdinakariitbbsacin, pdinakarrediffmailcom (P Dinakar), kartikiitbbsacin (M Kartik Reddy), muditiitbbsacin (M Sharma) Materials and Design 46 (2013) 609–616 Contents lists available at SciVerse ScienceDirect Materials and Design journal homepage: wwwelseviercom/locate/matdes  develop concretes by multi-unique characteristics, which wouldnot be attained in traditional NWC With the growth of buildingactivities in India there is severe cement crisis to meet the de-mands of the construction industry To meet the demands now adays almost all the major cement manufacturers are producingblended cements consisting of Portland pozzolana cement (PPC)and Portland slag cement (PSC) where PPC has a significant pres-ence in the Indian market as far as the production and usage is con-cerned Now there is an urgent need to design concretes usingthese blended cements to address the demands of the constructionindustry Therefore, an attempt was carried out herein to investi-gate the effect of fly ash replacements on the properties of SCCwhen PPC was used 3 Experimental studies  31 Materials The following materials were employed:   The cement used in all mixture was Portland pozzolana cement(PPC) conforming to IS 1489 Part 1 [18] The percentage blend-ing of fly ash in PPC is 28% In addition fly ash was also used as amineral additive Their chemical composition is specified inTable 1   Good quality aggregates have been procured for this investiga-tion Crushed granite with nominal grain size of 20 mm andwell-graded river sand of maximum size 475 mm were usedas coarse and fine aggregates, respectively The specific gravitiesof aggregates were determined experimentally The coarseaggregates with 20, 125 mm fractions had specific gravities of 291 and 280, whereas the fine aggregate had specific gravityof 273, respectively   Commercially available poly carboxylate ether (PCE) – basedsuper-plasticizer (SP) was used in all the concrete mixtures Itis an F-type high-range water reducer, in conformity withASTM: C 494  32 Mixture proportions Four SCC mixtures were designed in order to obtain differentfresh-statepropertiesThedetailsofthemixesforthestudyarepre-sented in Table 2 Four different mixes (SCC10, SCC30, SCC50 andSCC70) were employed to examine the influence of fly ash in SCCson the fresh, mechanical and durability properties when PPC ce-ment was used The water–binder ratio for all the mixes was keptconstant at 030 In mixes SCC10, SCC30, SCC50 and SCC70 cementcontent was replaced with 10%, 30%, 50% and 70% fly ash (by mass)respectively The essential component of SCC is a high range waterreducer (HRWRA) which is also known as superplasticizer SCCmixtures always include a high-range water-reducing admixture(HRWRA) to ensure concrete is able to flow under its own mass[19]Severaltrialmixeswereconductedtodeterminetheoptimumdosage of superplasticiser for each of the mixtures in order toachieve the required self compacting properties as per EFNARCstandardsThedosageofsuperplasticiserforeachmixwascarefullyselected as over dosage may induce bleeding and strength retarda-tion As far as the aggregate grading is concerned, in the presentinvestigation a combined aggregate grading as recommended bythe DIN 1045 [20] standards was utilised The aggregates 20, 125and 475 mm were combined in such a way, so that it meets nearlythecombinedgradingspecificationof DIN ‘B’curveThe percentagefractions of aggregates used for 20 mm – 21%, 125 mm – 30% and475 mm–49%ofthetotalaggregatecontentrespectivelyBlendingaggregates in this fashion will result in high strength cohesive self compactingconcretes[12]Effectofcoarseaggregateblendingwith20 mm and 10 mm on the short-term mechanical properties of SCChas also been carried out earlier [21]  33 Mixing and casting details All the materials were mixed using a pan mixer with a maxi-mum capacity of 80litres The materials were fed into the mixerin the order of coarse aggregate, PPC, fly ash and sand The materi-als were mixed dry for 15 min Subsequently three-quarters of thewater was added, followed by the superplasticiser and the remain-ing water while mixing continued for a further 6 min in order toobtain a homogenous mixture Upon discharging from the mixer,the self compactibility tests were conducted on the fresh proper-ties for each mixture The fresh concrete was placed into the steelcube moulds and compacted without any vibration Finally, surfacefinishing was done carefully to obtain a uniform smooth surface  34 Fresh concrete tests For determining the self-compactibility properties (slump flow, T  50  time, V-funnel flow time, L-box blocking ratio) tests were per-formed on all the mixtures The order of testing was:(a) Slump flow test and measurement of   T  50  time(b) V-funnel flow test(c) L-box blocking test, respectively The tests were performedin accordance with EFNARC [22] standards  35 Specimens and curing  The following specimens were cast from each mixture:   Three 100    100    100 mm cubes for the compressive strength   Three 100    200 mm cylinders for the splitting tensile test   Three 150    300 mm cylinders for the modulus of elasticitytest  Table 1 Chemical composition and physical properties of the Portland pozzolana cement(PPC) and fly ash Chemical composition PPC Fly ashCaO 457 17SiO 2  391 625Al 2 O 3  103 262Fe 2 O 3  582 42MgO 179 08SO 3  228 02Na 2 O 014 012K 2 O 071 114Loss in ignition 172 10 Physical properties Specific gravity 30 22Blaines fineness (m 2 /kg) 406 350Blending of fly ash in PPC 28 –  Table 2 Details of the mix proportions in kg/m 3 Constituent SCC10 SCC30 SCC50 SCC70Cement 495 385 275 165Water 165 165 165 165Fine aggregate 836 818 800 78320 mm 382 374 366 357125 mm 525 514 503 491Fly ash 55 165 275 385HRWR 66 715 715 880VMA 055 110 110 275610  P Dinakar et al/Materials and Design 46 (2013) 609–616     Two 100    100    100 mm cubes for water absorption study   Three 150    150    150 mm cubes for the water penetrationdepth test   Two 100    200 mm cylinders for the rapid chloride penetrabil-ity test Samples of 100    50 mm were prepared from thesecylindersAftercasting,all the specimenswerecovered withplasticsheetsand water saturated burlap, and left at room temperature for 24 hThe specimens were demoulded after 24 h of casting and werethen cured in water at approximately 27   C until the testing day  36 Test procedures The unconfinedcompressive strength wasobtained, at a loadingrate of 25 kN/s at the age of 3, 7, 28 and 90 days on 3000 kN ma-chine The average compressive strength of three specimens wasconsidered for each age The split tensile strength was also testedon the same machine at the age of 28 and 56 daysThe elastic modulus was determined at the age of 28 and56 days The specimens were fixed with a longitudinal compress-ometer, placed vertically between the platens of the compressiontesting machine and tested as shown in Fig 1 This test conformsto ASTM: C 469 for static modulus of elasticity of concrete in com-pression All the specimens were tested on saturated surface dryconditionThe water penetration depths under pressure were performedon150 mmcubesasperEN12390-8[23]at28and56 daysThetestmethod involves the study of water penetration on 15 cm cubesover a 5 bar pressure for a period of 72 h The experimental setupusedforthisstudywasshowninFig2Afterthetestthe specimenswere split exactly into two halves and the water penetration frontwas marked on the specimen as shown in Fig 3 The maximumdepthof penetrationunderthe test area wasdeterminedusingver-nier caliper and recorded it to the nearest millimetreThe absorption test was carried out on two 100 mm cubes asper ASTM: C 642 at 28 days of water curing Saturated surfacedry cubes were kept in a hot air oven at 100–110   C till a constantweight was attained These are then immersed in water and theweight gain was measured at regular intervals until a constantweight is reached The absorption at 30 min (initial surface absorp-tion) and final absorption (at a point when the difference betweentwo consecutive weights at 12 h interval was almost negligible) isreported to assess the concrete quality The final absorption in allcases is observed to be at 72 hThe rapid chloride penetrability test was conducted in accor-dance with ASTM: C 1202 These were also determined at 28 and56 days This test measures the ease with which concrete allowsthe charge to pass through and gives an indication of the concreteresistance to chloride-ion penetration Two specimens of 100 mmin diameter and 50 mm in thickness conditioned according to thestandard were subjected to 60 V potential for 6 h The total chargethat passed through the concrete specimens was determined andused to evaluate the chloride penetrability of each concrete mix-ture The reported results evaluated by the Coulomb charge arethe average of two tests 4 Test results and discussion 41 Fresh properties411 HRWR and VMA demand Table 3 presents the demand of HRWR and VMA admixturesused in all SCC mixtures It can be seen that the addition of flyash in Portland pozzolana cement has a significant influence onthe flow characteristics of SCC It can be observed that as the flyash content increases the demand for HRWR and VMA also in-creases For 70% replacement SCC demanded 16% and 05% of HRWR and VMA The reason could be that at 70% replacementthere was an abnormal increase in the paste volume of the SCC,this high paste volume is due to the low specific gravities of PPCand fly ash Also the PPC used in this investigation has got a veryhigh fineness of 406 m 2 /kg For 70% replacement several trailswere conducted to optimise the HRWR and VMA dosages Initiallyat low VMA dosage of around 02% the concretes seems to be cohe- Fig 1  Test set up for determining the elastic modulus Fig 2  Permeability test set up for determining the water penetration depth Fig 3  Water penetration dept front marked after the test P Dinakar et al/Materials and Design 46 (2013) 609–616   611