Project on Concrete Mix Design for various grades of Concrete
Answer (1):- 1: REQUIREMENTS OR STIPULATIONS TO BE KNOWN STRENGTH, MATERIALS TO BE USED, WORKABILITY, EXPOSURE CONDITIONS, MINIMUM AND MAXIMUM VALUES OF CEMENT AND WATER, IF SPECIFIED GRADE DESIGNATION M50
TYPE OF CEMENT
OPC 53 GRADE (IS-12269) TYPE OF MINERAL ADMIXTURE FLY ASH CONFIRMING TO IS 3812 PART-1
iv. MAXIMUM NOMINAL SIZE OF AGGREGATE 20MM
V. MINIMUM CEMENT CONTENT 320 KG/CUM FOR SEVERE EXPOSURE OF RCC
vi. MAXIMUM WATER CEMENT RATIO
vii. WORKABILITY 0.45 150-175MM SLUMP
viii. EXPOSURE CONDITION
ix.bMETHOD OF CONCRETE PLACING
X. DEGREE OF SUPERVISION
Xi. TYPE OF AGGREGATE SEVERE FOR RCC
PUMPING GOOD CRUSHED ANGULAR AGGREGATE
xii. MAX CONTENT (OPC CONTENT)
xiii. CHEMICAL ADMIXTURE TYPE 450 KG/CUM (IS 456) SUPERPLASTICISER (PC BASED-30% REDUCTION)
2: TEST DATA FOR MATERIALS SP GR OF-CEMENT, FLY ASH,CA,FA, ADMIXTURE WATER ABSORPTION OF CA AND FA SIEVE ANALYSIS OF CA AND FA FOR KNOWING GRADE AND ZONE.
i. CEMENT USED-OPC 53 GRADE CONFIRMING TO IS 12269
ii. SPECIFIC GRAVITY OF CEMENT 3.15
iii. FLY ASH CONFIRMING TO-IS 3812 PART-1
iv. SP. GR. OF FLY ASH
v. CHEMICAL ADMIXTURE TYPE SUPERPLASTICISER (PC BASED-30% REDUCTION)
vi. SP. GR. OF COARSE AGGREGATE 2.72
vii. SP. GR. OF FINE AGGREGATE - 2.72
viii. WATER ABSORPTION COARSE AGG. 0.6
ix. WATER ABSORPTION FINE AGG.1.3%
X FREE MOISTURE COARSE AGGREGATE NIL
Xi. CONSIDERED IN SSD CONDITION FREE MOISTURE FINE AGGREGATE NIL CONSIDERED IN SSD CONDITION
Xii. COARSE AGGRESSIVE 20 AND 10MM
CONFIRMING TO IS 383 TABLE-2
RATIO OF CA 20MM AND 10MM (60:40)
Xiii. FINE AGGREGATE (SAND)-CONFIRMING TO ZONE II TABLE 4 OF IS 383
STEP-1: FIND TARGET STRENGTH OF MIX USING fCK = fck+ 1.65 S WHERE fck is target average compressive strength at 28 days fck is characteristic compressive strength at 28 days Is standard deviation AS PER IS 10262 TABLE -1 S=5 FOR M30 TO M55 GRADES OF CONCRETE THEREFORE, TARGET STRENGTH fck' = 50+1.65X5=58 25
STEP-2:W/C RATIO FROM IS 456 TABLE-5 FROM TABLE-5 OF IS 456 MAXIMUM FREE WATER CEMENT RATIO IS 0.45 SEVERE EXPOSURE CONDITIONS AND 20MM NOMINAL SIZE OF AGGREGATE.
FOR THIS IS IRRESPECTIVE OF GRADE OF CONCRETE.WE MAY ADOPT LESSER W/C RATIO BASED ON EXPERIENCE. LET US ADOPT W/C RATION 0.42 BASED ON EXPERIENCE HERE. SINCE 0.42<0.45 HENCE OK.
STEP-3:WATER QUANTITY CALCULATION FOR GIVEN SLUMP AND
ADMIXTURE FROM TABLE-2 OF IS 10262 MAXIMUM FREE WATER CONTENT FOR 20MM NOMINAL SIZE OF AGGREGATE=186 KG (FOR 25 TO 50 MM SLUMP) ESTIMATED WATER CONTENT FOR 50-175 AM SLUMP÷186÷15% OF 186=213.9 |((BECAUSE AS PER
CODE WATER MAY BE INCREASED BY FOR EVERY ADDITIONAL 25MM SLUMP)
AS SUPERPLASTICISER IS BEING USED. REDUCTION IN WATER CONTENT UP TO 30%. TAKE REDUCTION.
THEREFORE, REDUCED WATER QTY 2139-25% 021-9-160.43 KG OR LITRE
STEP-4:CEMENT AND FLY-ASH CONTENT CALCULATION AS PER IS CODE 456W/C RATIO=0.42CEMENTITIOUS MATERIAL(CEMENT+FLY ASH) CONTENT =160.43/0.42=381.98||| KG WHICH IS THAN 320KG AS PER TABLE 5 CONDITIONS, HENCE OK.
REQD FOR SEVERE EXPOSURE NOW DECIDE THE % OF FLY ASH TO BE USED (LIMITS 15 TO 35%), HERE WE ARE USING ONLY 20% IN CERTAIN SITUATIONS INCREASE IN CEMENTITIOUS MATERIAL CONTENT MAY BE WARRANTED BASED ON EXPERIENCE AND TRIAL. HERE WE ARE INCREASING 15 CEMENTITIOUS MATERIAL CONTENT.
CEMENTITIOUS MATERIAL CONTENT=381.98X1.15-439.28 KG/CUM-WATER CONTENT=160.43 KG/CUMSO, WATER-CEMENT RATIO=160.43/439.28-0.365 WHICH IS <0.45 FLY ASH@ 20% OF TOTAL CEMENTITIOUS MATERIAL CONTENT-439.28X20%-87.86 KG/CUM CEMENT (OPC-53 GRADE)=439.28-87.86-351.42 KG/CUM
SO FAR WE HAVE CALCULATED
. QTY OF CEMENT
QTY OF FLY ASH
. QTY OF WATER
QTY OF ADMIXTURE GIVEN BY SUPPLIER
ONLY REMAINING IS
QTY OF COARSE AGGREGATE
QTY OF FINE AGGREGATE
NOW WE WILL CALCULATE OTY OF AGGREGATES
STEP-5:FIND VOLUME OF COARSE AGGREGATE
AND FINE AGGREGATE
FROM TABLE-3 OF IS 10262, VOLUME OF COARSE AGG CORRESPONDING TO 20MM SIZE AGG. AND FA(ZONE-2) FOR W/C RATIO OF 0.50 IS =0.62
IN THE PRESENT CASE W/C RATIO IS 0.42.
• THEREFORE, VOLUME OF COARSE AGG. IS REQD TO BE INCREASED TO DECREASE THE FA CONTENT.
AS THE W/C RATIO IS LOWER BY 0.08 FROM 0.50,THE PROPORTION OF VOLUME OF CA ISINCREASED BY (0.080/0.05)X0.01-0.016• (AT THE RATE OF -/+0.01 FOR EVERY +-0.05 CHANGE IN W/C RATIO) THEREFORE, CORRECTED PROPORTION OF VOLUME OF CA FOR W/C RATIO OF 0.42=0.60+0.016-0.616 FOR PUMPABLE CONCRETE THESE VALUES SHOULD BE REDUCED BY 10 PERCENT .THEREFORE ,AGGREGATE VOLUME OF COARSE=0.616X0.9=0.554AND THUS VOLUME OF FINE AGG. CONTENT=1-0.554-0.446 STEP-6: MIX CALCULATIONS-WEIGHTS OF DIFFERENT CONSTITUENTS THE MIX CALCULATIONS PER UNIT VOLUME OF CONCRETE SHALL BE AS FOLLOWS:VOL OF CONC. (A)=VOL. OF CEMENT (B)+VOL. OF FLY ASH(C)+VOL. OF WATER(D)+VOL OF CHEM ADMIX (E)+VOL OF ALL IN AGGREGATES(F) NOTE-AGGREGATES SHOULD BE USED
IN SATURATED SURFACE DRY
CONDITION (SSD). OTHERWISE
MOISTURE CORRECTION TO BE APPLIED
FOR FINE AND COARSE AGGREGATES.