Mix Design for Concrete Roads as Per IRC_15-2011

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  Posted inMix Design,Research Papers|Email This Post|  ByKaushal Kishore, Materials Engineer, Roorkee ABSTRACT: The stresses induced in concrete pavements are mainly flexural. Therefore flexural strength is moreoften specified than compressive strength in the design of concrete mixes for pavementconstruction. A simple method of concrete mix design based on flexural strength for normal weightconcrete mixes is described in the paper. INTRODUCTION: Usual criterion for the strength of concrete in the building industry is the compressive strength, which is considered as a measure of quality concrete.However, in pavement constructions, such as highway and airport runway, the flexural strength of concrete is considered more important, as the stressesinduced in concrete pavements are mainly flexural. Therefore, flexural strength is more often specified than compressive strength in the design of concrete mixes for pavement construction. It is not perfectly reliable to predict flexural strength from compressive strength. Further, various codes of theworld specified that the paving concrete mixes should preferably be designed in the laboratory and controlled in the field on the basis of its flexuralstrength. Therefore, there is a need to design concrete mixes based on flexural strength.The type of aggregate can have a predominant effect, crushed rock aggregate resulting in concrete with higher flexural strength than uncrushed (gravel)aggregates for comparable mixes, assuming that sound materials are used. The strength of cement influences the compressive and flexural strength of concrete i.e. with the same water-cement ratio, higher strength cement will produce concrete of higher compressive and flexural strength. MIX DESIGN DETAILS IRC: 15-2011 specified that for concrete roads OPC should be used. This code also allowed PPC as per IS: 1489 (Part-1) with flyash content not morethan 20 percent by weight of PPC. Accordingly OPC + fly ash may be used in concrete roads. Flyash shall be not more than 20 percent by weight of cementitious material. However, IS: 456-2000 specified that fly ash conforming to grade-1 of IS” 3812 may be used as part replacement of OPC provided uniform blended with cement is essential. The construction sites where batching plants are used this may be practicable. In ordinary sites where mixer or hand mixing are done uniform blending of fly ash with cement is not practicable. At such construction sites, PPC may be used. PPC should be used withcaution where rapid construction methods like slip form is being used. Joints cutting also need early strength.1Characteristic Flexural Strengthat 28 days:4.5 N/mm 2 2Cement:Three mixes are to be designed  MIX-A With PPC (Flyash 18 percent based)conforming to IS:1489-part-I-1991. 7 daysstrength 37.5 N/mm 2 . Specific Gravity :3.00 MIX-B With OPC-43- Grade conforming to IS:8112-1989. 7 days strength 40.5 n/mm 2 .Specific Gravity : 3.15 MIX-C With OPC of Mix-B and Fly ash conformingto IS:3812 (Part-I)-2003 Specific Gravity :2.20 Concrete Floor Profiler  www.Dipstick.comDipstick®Is the Most Accurate and the MostSpecified in 63 Countries Rotary Kiln Incinerator  www.rotary-dryer-machine.com/Minggong Rotary Kiln Incinerator Energy-saving,Reliable Supplier Concrete Batching Mixing www.conmixcrusher.comSpecialize Mobile Concrete Batching MixingPlant 12m3 to 42m3 Capacity Shine Heaven,Guwahati www.shinerealtors.comInvest in a dream home now! 1,2,3 BHK Available, 15-60 Lacs Mix Design For Concrete Roads As Per IRC:15-2011http://www.engineeringcivil.com/mix-design-for-concrete-roads-as-per-i...1 of 103/13/2013 7:49 PM  Note: Requirements of all the three mixesare the same. Fine Aggregate, CoarseAggregate and Retarder Super plasticizer arethe same for all the three mixes.3Fly ash replacement:20% Fly ash is required to be replaced withthe total cementitious materials.4Maximum nominal size of aggregates:31.5 mm Crushed aggregate5Fine aggregate and coarseaggregate grading:Given in Table 16Minimum cement content for 4.5 N/mm2 characteristic flexuralstrength::(a) OPC shall not be less than 360 kg/m 3 .(b) PPC shall not be less than 425 kg/m 3 .Fly ash in it 20% maximum by weight of total cementitious materials(c) OPC + Fly ash mix OPC shall not beless than 340 kg/m 3 . Fly ash 20% maximum by weight of cementations material7Maximum free W/C Ratio:(a) For OPC 0.45(b) For PPC 0.508Workability:40 mm slump at pour the concrete will betransported from central batching plantthrough transit mixer, at a distance of 15 Kmduring June, July months. The averagetemperature last year during these monthswas 30 0 C.9Exposure condition:Moderate10Method of placing:Fully mechanised construction11Degree of supervision:Good 12Maximum of cement content:(a) OPC 425 kg/m 3 (b) PPC 425 kg/m 3 13Chemical admixture:Retarder Super plasticizer conforming toIS:9103-1999. With the given requirementsand materials, the manufacturer of Retarder Super plasticizer recommends dosages of 1% bw of OPC, which will reduce 15% of water without loss of workability. For flyash included cement dosages will berequired to be adjusted by experience/trials.2% maximum by weight of cementitious material14Values of Z x (for NationalHighway):1.96 x 0.40 TEST DATA FOR MATERIALS AND OTHER DETAILS 1. The grading of fine aggregate, 1 & 2 aggregates are as given in Table. 1.2. Properties of aggregatesTestsFine aggregateAggregate 1Aggregate 2Specific Gravity2.652.652.65Water Absorption %0.80.50.53. Target average flexural strength for all A, B and C mixesS = S+ Zq =4.5 + 1.96 x 0.40 Mix Design For Concrete Roads As Per IRC:15-2011http://www.engineeringcivil.com/mix-design-for-concrete-roads-as-per-i...2 of 103/13/2013 7:49 PM  = 5.3 N/mm 2 at 28 days age4. For Mix A, B and C free W/C ratio with crushed aggregate and required average flexural target strength of 5.3 N/mm 2 at 28 days from Fig. 1 Curve Dfound to be 0.42. This is lower than specified maximum W/C ratio value of 0.45 for OPC and 0.50 for PPC. Note:In absence of cement strength, but cement conforming to IS Codes, assume from Fig. 1Curve C and D for OPC 43 GradeTake curves C and D for PPC, as PPC is being manufactured in minimum of 43 Grade of strength.5. Other data’s: The Mixes are to be designed on the basis of saturated and surface dry aggregates. At the time of concreting, moisture content of siteaggregates are to be determine. If it carries surface moisture this is to be deducted from the mixing water and if it is dry add in mixing water the quantityof water required for absorption. The weight of aggregates are also adjusted accordingly. DESIGN OF MIX-A WITH PPC a) Free W/C ratio for the target flexural strength of 5.3 N/mm 2 as worked out is 0.42 for first trial. b) Free water for 40 mm slump from Table 2 for 31.5 mm maximum size of aggregate.2/3×170 + 1/3×200= 180 kg/m 3 From trials it is found that Retarder Super plasticizer at a dosages of 1.3% bw of PPC may reduce 15% water without loss of workabilityThen water = 180 – (180 x 0.15) = 153 kg/m 3 c) PPC = 153/0.42 = 364 kg/m 3 (Required minimum PPC is 425 kg/m 3 )d) Formula for calculation of fresh concrete weight in kg/m 3 U m = 10 x G a (100 – A) + C m (1 – G a /G c ) – W m (Ga – 1)Where,U m =Weight of fresh concrete kg/m3G a =Weighted average specific gravity of combined fine and coarse aggregate bulk, SSDG c =Specific gravity of cement. Determine actual value, in absence assume 3.15 for OPC and 3.00 for PPC (Fly ash based)A=Air content, percent. Assume for trial entrapped air 1.5%For 31.5 mm maximum size of aggregateThere is always entrapped air in concrete. Therefore ignoring entrapped air value as NIL will lead the calculation of higher value of density. Take exactvalue of air as obtained in the testW m =Mixing water required in kg/m 3 C m =Cement required, kg/m 3  Note:- The exact density may be obtained by filling and fully compacting constant volume suitable metal container from the trial batches of calculated design mixes. The mix be altered with the actual obtained density of the mix.U m =10 x G a (100 – A) + C m (1 – G a /G c ) – W m (G a – 1)=10 x 2.65 (100 – 1.5) + 425(1- 2.65/3.00) – 153 (2.65 -1)=2409 kg/m 3 e) Aggregates = 2409 – 425 – 153 = 1831 kg/m 3 f) Fine aggregate = 1831 x 0.45 = 824 kg/m 3 Aggregate 1 = 1831 x 0.29 = 531 kg/m 3 Aggregate 2 = 1831 x 0.26 = 476 kg/m 3 g) Thus for 4.5 N/mm2 flexural strength quantity of materials per cu.m. of concrete on the basis of saturated and surface dry aggregates: Water = 153 kg/m 3 PPC = 425 kg/m 3 Fine Aggregate (sand) = 824 kg/m 3 Aggregate (1) = 531 kg/m 3 Aggregate (2) = 476 kg/m 3 Retarder Super Plasticizer 1.3% bw of PPC = 5.525 kg/m 3 MIX- B WITH OPC a) Water = 180 – (180 x 0.15) = 153 kg/m 3 Mix Design For Concrete Roads As Per IRC:15-2011http://www.engineeringcivil.com/mix-design-for-concrete-roads-as-per-i...3 of 103/13/2013 7:49 PM   b) OPC = 153/0.42 = 364 kg/m 3 c) Density: 10 x 2.65 (100 – 1.5) + 364 (1 – 2.65/3.15) – 153 (2.65 – 1)= 2416 kg/m 3 d) Total Aggregates = 2416 – 364 – 153 = 1899 kg/m 3 Aggregate 1 = 1899 x 0.29 = 551 kg/m 3 Aggregate 2 = 1899 x 0.26 = 494 kg/m 3 Fine Aggregate = 1899 x 0.45 = 854 kg/m 3 e) Thus for 4.5 N/mm 2 flexural strength quantity of materials per cu.m of concrete on the basis of SSD aggregates are given below: Water = 153 kg/m 3 OPC = 364 kg/m 3 Fine Aggregate (sand) = 854 kg/m 3 Aggregate (1) = 551 kg/m 3 Aggregate (2) = 494 kg/m 3 Retarder Super Plasticizer 1% bw OPC = 3.640 kg/m3 MIX-C WITH OPC + FLY ASHWith a total cementitious material of 430 kg/m 3 ,OPC = 430 x 0.80 = 344 kg/m 3 Fly ash = 430 x 0.20 = 86 kg/m 3 Mix on the basis of SSD Aggregates,(1) Water as worked out earlier = 153 kg/m 3 (2) OPC = 344 kg/m 3 (3) Fly ash = 86 kg/m3Density = 10 x 2.65 (100 – 1.5) + 430 (1 – 2.65/3.00) – 153 (2.65 – 1) = 2410 kg/m 3 Total Aggregates = 2410 – 153 – 344 – 86 = 1827 kg/m 3 (4) Fine aggregate 0.45 x 1827 = 822 kg/m 3 (5) Aggregate (1) 0.29 x 1827 = 530 kg/m 3 (6) Aggregate (2) 0.26 x 1827 = 475 kg/m 3 (7) Retarder super plasticizer 1.5% bw of cementitious material = 6.450 kg/m 3  Note:(1) Cementitious material worked out as per IRC : 15-2011, which specified: In case fly ash (as per IS: 3912 Part 1) is blended at site, the quantity of flyash shall be restricted to 20 percent by weight of cementitious material and the quantity of OPC in such a blend shall not be less than 340 kg/m 3 .(2) After the first trial mix, its actual density is to be determined, as specified elase where in this paper. The mix proportions shall then be worked outaccordingly including the water content, the dosages of Retarder SP for required workability keeping the free w/c ratio with in the permissible limits and adjusting it according to the required flexural strength.(3) The mix proportions given in this paper are for first trial and to be adjusted as per actual site materials, conditions and requirements. For 4.5 N/mm 2 flexural strength quantity of material per cu.m of concrete on the basis of saturated and surface dry aggregates of Mix ‘A’, ‘B’and ‘c’ are given below: MaterialsMIX. ‘A’ with PPCMix. ‘B’ with OPCMix. ‘C’ withOPC+FlyashWater kg/m 3 153153153PPC kg/m 3 425–– OPC kg/m 3  –364344Flyash kg/m 3  ––86Fine Agg. kg/m 3 824854822Agg. (1) kg/m 3 531551530 Mix Design For Concrete Roads As Per IRC:15-2011http://www.engineeringcivil.com/mix-design-for-concrete-roads-as-per-i...4 of 103/13/2013 7:49 PM
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