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By : Dr.(Mrs.) V. Tare Professor. Civil Engg. & applied Mechanics Deptt. ,S.G.S.I.T.S. ,Indore 1 Process of selecting suitable ingredients of concrete and determining their relative proportions with object of producing concrete of certain minimum strength and durability as economically as possible. 2 Concrete mix proportion should be such as to ensure the workability of the fresh concrete and when concrete is hardened it shall have the required strength, durability and surface finish. DMC (Design Mix Concrete) NMC (Nominal Mix Concrete) ≤ M20 – nominal may be used with permission of engineer in-charge and likely to consume more cement. 3 W/C ratio Cement content or Aggregate Cement ratio Gradation of Aggregate Workability Admixtures 4 5 Minimum --- will lubricate the mass while fresh and after hardening will bind the aggregate Particles together and fill the space between them. More --- Excess paste greater cost, greater drying shrinkage, greater susceptibility to percolation of water. Aggregate Cement ratio 1:2:4 --- A/C =6 1:1.5:3 --- A/C = 4.5 6 Minimum voids. Well graded agg. Minimum voids --- will require minimum paste--- less cement ----economy Paste is weaker link in concrete If paste is more --- permeable, attack of aggressive chemicals, greater drying shrinkage, more cost, hence importance of good grading. Sieve analysis is done Grading limits for CA. IS-383 Grading limits of fine agg. IS-383 7 8 9 A workable conc. is one that in cohesive, flows well, and without segregation be fully compacted. It depends on types of aggregate – rounded, angular, flaky grading of CA & FA Quantity of cement paste Consistency of the paste 10 CF 0.75 TO 0.80 UsingFlowTable 11 Plasticizers Superplastisizers Grouting Admixtures Pozzolonic Admixtures Fungicidal, germicidal and insecticidal 12 The action of plasticizer is mainly to fluidify the mix and improve the workability of concrete, mortar or grout. When Plasticizers are used ,they get adsorbed on the cement particles. The adsorption of charged polymer on the particles of cement creates particle-to-particle repulsive forces which overcome the attractive forces. This repulsive forces called Zeta Potential. the overall result is that the cement particle are deflocculated and dispersed. when cement particles are deflocculated, the water trapped inside the flocs gets released and now available to fluidity the mix 13 The mechanism of action of super plasticizer are more or less same as ordinary plasticizer. Only thing is that the super plasticizer are more powerful as dispersing agents and they are high range water reducers. 14 In concrete variables are material and construction process. Strength varies from batch to batch & within batch. The aim of quality control is to limit the variability as much as practicable. The basis of acceptance of sample is that a reasonable amount of concrete work can be provided by ensuring probability of test result falling below the design strength is not more than a specific tolerance level. Assumed standard deviation as per IS 456-200. 15 Grade of conc. M10 M15 M20 M25 M30 M35 M40 M45 M50 Assumed standard deviation N/mm2 3.5 4.0 5.0 16 Target strength = fck + ks fck= characteristics compressive strength k = Himsworth constant s = standard deviation 17 Percentage of results below the characteristic strength k 50 0 16 1 10 1.28 6.6 1.5 5 1.65 2.5 1.96 1.0 2.33 0.5 2.58 0 Infinity Target strength = Fck+1.65s 18 IS method ACI method DoE method Murdock method 19 Data required:Characteristics compressive strength fck Maximum Size of agg. shape of agg. workability Type of exposure Sp. Gravity Of cement Sp. Gravity Of FA. Sp. Gravity Of CA. 20 1.)Target mean strength = fck + ks 2.)Selection of W/C ratio (graph is available) 21 3. Estimation of entrapped air :Max. size of agg.(mm) Entrapped air as % of volume 10 3.0 20 2.0 40 1.0 22 4.) Selection of water content and fine to total aggregate:- 23 5.) Correction applied for water content and fine to total aggregate :Change in condition Stipulated For tables Adjustment required in Water content % Sand in Total Aggregate For sand conforming to grading zone I, zone III or zone IV of table 4, IS:383-1979 0 +1.5% for Zone I -1.5% for Zone III -3% for Zone IV Increase or decrease in the value of compacting factor by 0.1 ` 3% 0 Each 0.05 increase or decrease in water-cement ratio 0 ` 1% -15kg -7% In water-cement ratio for rounded aggregate 24 6.)Calculation of cement content Cement Content = Water Content / W/C ratio 7.)Calculation of aggregate content :V = [W+(C/Se)+(1/P) x(FA/Sfa)]x(1/1000) CA = (1-p)/p)x(FA)x(Sca/Sfa) 8.)Calculation of mix proportion 25 Example:Design data : Characteristic comp. strength Fck = 30mpa MSA = 20mm Degree of workability = 0.85 (CF) Sp. gravity of cement = 3.15 Sp. gravity of fine agg.= 2.7 Sp. gravity of coarse agg. = 2.7 26 Steps of design 1) Target mean strength = 30+1.64x4=36.6 MPa 2) W/C ratio from graph = 0.45 3) Selection of water content = 175 kg/cum 4) Percent sand = 35% 5) Change in condition Change in condition Percent adjustment required Water content Sand in total aggregate For decrease in w/c ratio by (0.60-0.45) that is for (-0.15) 0 -3.0 (` 1% for w/c=0.6) For increase or decrease in compacting factor (0.8-0.85),that is for (+ 0.05) +1.5 (` 3%for cf=0.8) 0 For sand conforming zone ii of table 4, IS:383-1970 0 0 Total +1.5 -3.0 27 Therefore required sand content as percentage of total aggregate by absolute volume = 35 - 3.0 = 32.0 Required water content = 175 + (175 x 1.5/100) = 177.62 kg/cum 6.Determination of cement content :W/C ratio = 0.45 Water = 177.62 ltr Cement = 177.62 /0.45 = 394.7 = 395 kg/cum (say) 28 7.Determination of fine and coarse aggregate contents:0.98=[177.62 +(395/3.15)+(1/0.32) x(FA/2.7)]x(1/1000) 980=[177.62 +125.4+FA/0.864] FA= [980- 177.62 -125]x0.864 FA= [980- 303]x0.864 = 585 kg(say) Ca = [(1-0.32)/.32] x 585 x 2.7/2.7 ] = 2.125 x 585 = 1243 29 8.Proportion :Cement: Sand: agg 395 : 585 : 1243 1 : 1.48 : 3.15 By Weight [(1x1400)/ 1400] : [(1.48 x 1400)/1600] : [(3.15 x 1400)/1800] By volume 30 The code includes the use of 10 types of cement OPC,RHPC,PSC(Portland Slag Cement),PPC (fly ash based),PPC (calcined clay based),HC (Hydrophobic Cement), LHPC (Low Heat Portland Cement), SRPC (Sulphate Resistance Portland Cement). Aggregate should comply with IS 383. For RCC 20 mm aggregate is mostly used, sometime 40 mm may be permitted. Potable water should be used for making concrete. Admixtures if used should comply with IS 9103. 31 Min. grade of concrete should not be less than M20 for RCC works. M10,M15,M20- Ordinary Concrete. M25-M55- Standard Concrete. M60-M80- High Strength Concrete. Flexural Strength= 0.7 X (fck)1/2 fck – Cube Compressive Strength N/mm2 EC=5000 (fck)1/2 32 Thermal Expansion 0C (10-5) Quartzite=1.2-1.3 Granite=0.7-0.95 Sand Stone=0.9-1.2 Basalt=08-0.95 Lime Stone=0.6-0.9 Workability has been specified in terms of slumps mm. Durability clause has been enlarged. Exposure-mild, moderate, severe, very severe, Extreme. 33 Data required :Characteristics compressive strength fck Maximum Size of agg. shape of agg Type of exposure workability (Slump) Sp. Gr. Of cement Sp. Gr. Of FA Sp. Gr. Of CA Finess modulus of fine aggregate Bulk density of dry roded coarse aggregate 34 1.)Target mean strength = fck + ks 2.)Selection of W/C ratio 35 36 3.) for given slump at MSA find out water content in kg/cum 37 4.) find out cement content in kg/cum= water content /water cement ratio 5.) for msa and Finess modulus of sand find out bulk volume of dry rodded coarse aggregate per unit volume of concrete 38 6.) find out weight of coarse aggregate CA= result of step 5 x bulk density of dry rodded coarse aggregate in kg/cum 7.) From density of concrete calculate (FA = Density – cement – Coarse Aggregate – water ) kg/cum 8.) Proportion = Cement : Fine agg. : Coarse agg. 9.) Allowance for bulking, water absorption, moisture content, evaporation are made in field. 39 40