3Cement Concrete Mix Design means, determination of the proportion of the concrete ingredients i.e. Cement, Water, Fine Aggregate,Coarse Aggregate which would produce concrete possessing specified properties such as workability, strength and durability with maximum overall economy.
4Methods of Concrete Mix Design I.S. MethodBritish MethodA.C.I. Method etc.
5These Methods are based on two basic assumptions Compressive Strength of Concrete is governed by its Water-Cement RatioWorkability of Concrete is governed by its Water Content
6Data required for concrete mix design Grade of ConcreteEg: RCC-M30-A20Slump required in mmEg: 25 – 75 mmDegree of Site ControlEg: GoodType of ExposureEg: ModerateGrade of CementEg: OPC 43 Grade
7Workability (Clause 7.1, IS:456-2000) Placing Conditions Degree of WorkabilitySlump (mm)123Blinding Concrete;Shallow Sections;Pavements using paversVery LowSee 7.1.1Mass Concrete;Lightly reinforced sections in Slabs, Beams, Walls, Columns; Floors;Hand placed Pavements;Canal lining; Strip FootingsLow25-75Heavily reinforced sections in Slabs,Beams, Walls, Columns;Slip form work; Pumped Concrete.Medium50-100Trench fill; In-Situ Piling; Tremie ConcreteHigh
8Degree of Site Control (Table 8, IS:456-2000) Good Site control having proper storage of cement;weigh batching of all materials;Controlled addition of water,regular checking of all materials,aggregate grading and moisture content;And periodical checking of workability and strength.FairSite control having deviation from the above.
9Type of Exposure (Table 3, IS:456-2000) Sl.No.EnvironmentExposure Conditions123i)MildConcrete surfaces protectedagainst weather or aggressive conditions,except those situated in coastal area.ii)ModerateConcrete surfaces sheltered from severe rain or freezing whilst wet.Concrete exposed to condensation and rain.Concrete continuously under water.Concrete in contact or buried under non-aggressive soil/ground water.Concrete surfaces sheltered from saturated salt air in coastal area.iii)SevereConcrete surfaces exposed to severe rain, alternate wetting and drying or occasional freezing whilst wet or severe condensation.Concrete completely immersed in sea water.Concrete exposed to coastal environment.iv)Very SevereConcrete exposed to sea water spray, corrosive fumes or severe freezing conditions whilst wet.Concrete in contact with or buried under aggressive sub-soil/ground water.v)ExtremeSurface of members in tidal zone.Members in direct contact with liquid/solid aggressive chemicals.
10Approximate Quantity of Materials required for concrete mix design Cement : 200 Kg.Fine Aggregate : 240 Kg.Coarse Aggregate : 180 Kg. (20 mm)180 Kg. (10 mm)
11STEPS INVOLVED IN CONCRETE MIX DESIGN Step I:- Determine the physical properties ofconcrete ingredients.I. CEMENT (OPC 43 Grade)Sl.No.Particulars of TestResultSpecificationsAs per IS:1Standard consistency(% by weight)25.62Setting Time in minutesa) Initialb) Final9521030 Minimum600 Maximum3Compressive Strength in N/sq.mm at the age ofa) 3 daysb) 7 daysc) 28 days24354623 Minimum33 Minimum43 Minimum4Specific Gravity3.005Fineness in Sq.m/Kg337225 Minimum
12Specifications for Zone–II FINE AGGREGATE1. Sieve AnalysisSieve Size% PassingSpecifications for Zone–IIAs per IS:10.0 mm1004.75 mm90-1002.36 mm9875-1001.18 mm6555-90600 micron4235-59300 micron88-30150 micron0-102. Specific Gravity : 2.603. Unit Weight in Kg/Cu.ma) Loose : 1460b) Rodded : 15804. Materials Finer than 75 micron : Max(% by weight)
13III. 20.0mm COARSE AGGREGATE 1. Sieve Analysis Sieve Size% PassingSpecificationsAs per IS:GradedSingle Sized40.00mm10020.00mm9095-10085-10010.00mm325-550-204.75mm0-100-52. Specific Gravity : 2.653. Unit Weight in Kg/Cu.ma) Loose : 1467b) Rodded : 1633
14IV. MECHANICAL PROPERTIES Sl.No.Particulars of TestResultSpecificationsAs per IS:1Crushing Value in %2830 MaximumFor wearing surfaces45 MaximumFor other concrete2Impact Value in %243Los Angeles Abrasion Value in %3050 Maximum
15V. 10.0mm COARSE AGGREGATE 1. Sieve Analysis 2. Unit Weight in Kg/Cu.m Sieve Size% PassingSpecificationsAs per IS:GradedSingle Sized12.50mm100–10.00mm8585-1004.75mm190-202.36mm0-52. Unit Weight in Kg/Cu.ma) Loose : 1427b) Rodded : 1587
16VI. BLENDING OF COARSE AGGREGATE: Sieve size(mm)IS:Specifications(Graded)% Passing20 mm10 mm60%+40%50%+50%401002095-1009094951025-55385444.750-10197
17Step II:- Compute Target Mean Compressive Strength: Fck = fck + t * SFck = Target Mean Compressive Strength at 28 days inN/Sq.mmfck = Characteristic Compressive Strength at 28 days inS = Standard Deviation in N/Sq.mmt = A Statistic, depending on accepeted proportion oflow results.= for 1 in 20 accepted proportion of lowresults
18Accepted proportion of low results Values of tAccepted proportion of low resultst1 in 5, %0.841 in 10, 10%1.281 in 15, %1.501 in 20, 5%1.651in 40, %1.861 in 100, 1%2.33
19Assumed Standard Deviation (Table 8, IS: )Grade of ConcreteAssumed Standard Deviation(N/Sq.mm)Good Site ControlFair Site ControlM10, M153.54.5M20, M254.05.0M30, M35M,40,M45M506.0
20Step III:- Select the Water-Cement ratio of trial mix from experience No.ConcreteGradeMinimum expected W/C1M100.92M150.73M200.554M250.505M300.456M350.407M400.358M450.30
21Maximum size of Aggregate Water Content per cubic metre of concrete Step IV:- Select the water content per cubic metre ofconcrete from table2 of I.S:Maximum size of Aggregate(mm)Water Content per cubic metre of concrete(Kg)102082018640165
22Maximum Size of Aggregate Approximate water content (Kg)per cubic metre of concrete(Table 32, SP: )Slump(mm)Maximum Size of Aggregate10204030-5020518516080-100225200175240210
23Volume of Coarse Aggregate per Unit Volume of Total Aggregate (Table 3, IS: )Maximum Size of Aggregate(mm)Volume of Coarse Aggregate per Unit Volume of Total AggregateZone IVZone IIIZone IIZone I100.500.480.460.44200.660.640.620.60400.750.730.710.69
25Step V:- Compute the quantity of cement as follows. WaterCement =W/C Ratio= 185 / 0.45 = 411 Kg.
26Step VI:- Then we find the quantities of Fine & Coarse aggregate by absolute volume method. V = (W+C/Sc+(1/p) * (fa/Sfa)) * (1/1000) (Eq.1)andV = (W+C/Sc+(1/(1-p)) * (ca/Sca)) * (1/1000) (Eq.2)WhereV = Absolute volume of fresh concrete = 1 m3W = Mass of Water (Kg) per m3 of concreteC = Mass of Cement (Kg) per m3 ofconcretep = Percentage of fine aggregate.fa = Mass of fine aggregateca = Mass of coarse aggregateSc = Specific gravity of cement.Sfa = Specific gravity of fine aggregate.Sca = Specific gravity of coarse aggregate.
27Substituting the values in Eq(1), we get 1000 = /3.0 + (1/0.36) * fa /2.6)= fa/0.936= fa/0.936fa = (1000 – 322) * 0.936= 678 * 0.936= 635 Kg.
28Substituting the values in Eq(2), we get 1000 = /3.0 + (1/0.64) * ca /2.65)= ca/1.696= ca/1.696ca = (1000 – 322) * 1.696= 678 * 1.696= 1150 Kg.
29So the mix proportion works out to be W : C : fa : ca= 185 : 411 : 635 : 1150= : 1 : 1.55 : 2.80This mix will be considered as Trial Mix No.2
30Step VII:- Make slump trials to find out the actual weight of water to get required slump. Make corrections to the watercontent & %FA, if required.Step VIII:- Compute 2 more trial mixes with W/C ratios as 0.40 &0.50, taking %FA as 34% and 38% respectively.
31Trial Mix No. 1:-Cement = 185 / 0.4 = Kg.Substituting the values in Eq(1), we get1000 = /3.0 + (1/0.34) * fa /2.6)fa = 584 Kg.Substituting the values in Eq(2), we get1000 = /3.0 + (1/0.66) * ca /2.65)ca = 1156 Kg.So the mix proportion works out to beW : C : fa : ca= 185 : : 584 : 1156= 0.4 : 1 : 1.26 : 2.50
32Trial Mix No. 3:-Cement = 185 / 0.5 = 370 Kg.Substituting the values in Eq(1), we get1000 = /3.0 + (1/0.38) * fa /2.6)fa = 683 Kg.Substituting the values in Eq(2), we get1000 = /3.0 + (1/0.62) * ca /2.65)ca = 1136 Kg.So the mix proportion works out to beW : C : fa : ca= 185 : 370 : 683 : 1136= 0.5 : 1 : 1.85 : 3.07
33Step IX:- Cast atleast 3 cubes for each trial mix. Step X:- Test the cubes for compressive strength at 28 days.
3428 Days Compressive Strengths of Trial Mixes W/C RatioC/W RatioCompressive Strength(Kg/Cm2)0.402.504570.452.224200.502.00360
35Step XI:- Draw a graph between compressive strength Vs C/W Ratio.
37Step XII:- From the graph, find the W/C ratio for the required target mean compressive strength.Step XIII:- Calculate the mix proportions corresponding tothe W/C ratio, obtained from the graph.
38Final Mix:-From the graph, for a target strength of 390 Kg/Cm2, W/C ratio = 0.47Cement = 185 / 0.47 = 394 Kg.Substituting the values in Eq(1), we get1000 = /3.0 + (1/0.38) * fa /2.6)fa = 675 Kg.Substituting the values in Eq(2), we get1000 = /3.0 + (1/0.62) * ca /2.65)ca = 1123 Kg.So the mix proportion works out to beW : C : fa : ca= 185 : 394 : 675 : 1123= : 1 : 1.71 : 2.85
39Step XIV:- Check the cement content & W/C ratio against the limiting values given in Table-5 of I.S: for given type of exposure & type of Concrete.
40Table-5 Minimum Cement content Maximum Water-Cement ratio and Minimum Grade of Concrete for different exposures with normal weight of aggregate of 20mm nominal maximum size.Sl.No.ExposurePlain ConcreteReinforced ConcreteMinimum Cement Content kg/m3Maximum Free Water Cement RatioMinimum Grade of Concretei)Mild2200.60-3000.55M20ii)Moderate240M150.50M25iii)Severe2503200.45M30iv)Very Severe260340M35v)Extreme2800.40360M40
41The W/C Ratio = 0.47 < 0.5 Hence Ok From the table 5 of IS: 456–2000, the minimum Cement content & W/C ratio, For moderate, for RCC are 300Kgs. & 0.5The Cement content = 394Kgs. > 300Kgs. Hence OkThe W/C Ratio = 0.47 < 0.5 Hence Ok
42Concrete Mix RCC M30 with 20.0mm M.S.A. TEST REPORTConcrete Mix RCC M30 with 20.0mm M.S.A.Sl.No.ParticularsResult1Characteristic Compressive strength in N/Sq.mm302Maximum size of Aggregate in mm20.03Type of ExposureModerate4Type of Site controlGood5Target Average Compressive Strength in N/Sq.mm38.26Workability in terms of Slump in mm25-757Mode of CompactionVibration8Mix Partiuclars:a. Water-Cement Ratiob. Materials per cubic metre of concrete in Kg.i) Waterii) Cement (OPC 43 Grade)iii) Fine Aggregateiv) Coarse Aggregatec. Mix Portion by weight0.4718539467511231:1.71:2.85
49The value of ‘S’ depends on Degree of Site control and grade of concrete as given in I.S: 456–2000 (Table.8)Sl.No.ConcreteGradeGoodFairS1.65XSFckN/mm2Kg/cm21M103.55815.81614.57.417.41782M1520.821222.42293M204.06.626.62715.08.328.32884M2531.632233.33395M3038.33906.09.939.94076M3543.344144.9458
50Step IV:-Fixation of Water Cement ratios for trial mixes. Sl.No.Required GradesTrial W/C1M20, M15, M100.55, 0.6, 0.92M25, M20, M150.5, 0.6, 0.7
51Final Mix for RCC-M25:-From the graph, for a target strength of 322 Kg/Cm2, W/C ratio = 0.57which is > 0.5, So, limit W/C ratio to 0.5 only.Cement = 185 / 0.5 = 370 Kg.Substituting the values in Eq(1), we get1000 = /3.0 + (1/0.38) * fa /2.6)fa = 683 Kg.Substituting the values in Eq(2), we get1000 = /3.0 + (1/0.62) * ca /2.65)ca = 1136 Kg.So the mix proportion works out to beW : C : fa : ca= 185 : 370 : 683 : 1136= : 1 : 1.85 : 3.07
52Specific Gravity of Cement [ IS : 4031 – 1988]: Specific gravity of cement (Sc)(W2 - W1)= x 0.79(W4 - W1) - (W3 - W2)Where,W1 = Weight of specific gravity bottle in gW2 = Weight of specific gravity bottle with about half filled cement in gW3 = Weight of specific gravity bottle with about half filled cement& rest is filled with kerosene in g.W4 = Weight of specific gravity bottle completely filled with kerosene in g0.79 = Specific Gravity of Kerosene.
53Specific Gravity of Fine Aggregate & Coarse Aggregate [ IS : 2386 (Part.3) - 1963]: DSpecific gravity (Gs) =C – ( A – B)Where,A = Weight of Pycnometer vessel containing sample & filled with distilled water in gB = Weight of Pycnometer completely filled with distilled water only in gC = Weight of saturated surface dry sample in gD = Weight of oven dried sample in g