As per latest code IS 10262 : 2019

Projects requirements

  • High strength Concrete of M70
  • Type of cement used OPC 53 grade cement conforming to IS 269
  • Silica Fume ( Advantageous for grades M50 and above) Conforming to IS 15388.
  • Maximum nominal size of aggregate : 20 mm. 
  • Exposure condition : Severe exposure condition defined as per table 3 Page no 18 of IS 456 2000 . Requirements for RCC in severe exposure condition as per table 5 Page no 20 IS 456 2000
  • Workability : 120 mm (slump)
  • Method of concrete placing : Pumping
  • Degree of supervision : Good
  • Type of aggregate : Crushed angular aggregate
  • Maximum cement content : 450 kg per cum
  • hemical admixture type : Super-plasticizer (Polycarboxylate ether based)

Basis for design calculations

  • Material properties
  • Specific gravity of cement : 3.15
  • Specific gravity of coarse aggregate (at SSD conditions ) : 2.74
  • Specific gravity of Fine sand ( at SSD condition) : 2.65
  • Specific gravity of fly ash : 2.20
  • Specific gravity of Silica fume : 2.20
  • Specific gravity of Chemical admixture : 1.08
  • Water absorption of coarse aggregate : 0.5 percent
  • Water absorption of fine aggregate : 1.0 percent
  • Moisture content of coarse and fine aggregate : NIL

Aggregate properties

  1. Sieve analysis of coarse aggregate Conforming to Table 7 page no 6 of IS 383 2016 i). 90 to 100 percent passed from 20 mm IS Sieve ii)25 to 55 percent passed from 10 mm IS sieve iii). 0 to 10 percent passed from IS sieve
  2. Sieve analysis of Fine aggregate conforming to Grading Zone II of Table 9 page 7 of IS 383 2016 i). 90 to 100 percent passed from 4.75 mm IS Sieve ii). 75 to 100 percent passed from 2.36 mm IS sieve no iii). 55 to 90 percent passed from 1.18 mm IS Sieve. iv). 35 to 59 percent passed from 600 micron IS Sieve v). 8 to 30 percent passed from 300 micron IS Sieve vi). 0 to 10 percent passed from 150 micron IS Sieve

Target Strength for Mix Proportioning as per clause number 4.2 Page no 02 of IS 10262 : 2019

As per IS 10262 : 2019 Table 1 and Table 2 of page no 3 F’ck = fck + 1.65 X Standard deviation
OR
F’ck = fck + factor based on grade of high strength concrete of m70, whichever is higher For M70 grade concrete Factor based on grade of concrete = 8.00
Standard Deviation = 6.00 F’ck= 70 + 1.65 X 6 = 79.90 N/mm2
F’ck = 70 + 8 = 78.00 N/mm2. Hence higher value of F’ck = 79.90 N/mm2 is to be used for design calculations As per Table 1 para 2 page 3 of IS 10262:2019 (for grades M65 and above, the standard deviation may also be established by actual trials based on assumed proportions , before finalizing the mix)

Approximate Air content

As per clause number 6.2.3 Table no 6 ,page no 7 of IS 10262 : 2019
For 20 mm nominal maximum size of aggregate, 0.5 percent of entrapped air of total volume of concrete. If site data is available then actual values of air content can also be adopted

Calculations of cement content

Water content (As per Table 4 , page no 5 of IS 10262 ) for 20 mm nominal maximum size of saturated surface dry aggregate is 186 kg per cum ( for 50 mm slump without using superplasticiser ) . As per clause number 6.2.4 , page no 8 of IS 10262: 2019 , For the desired workability other than 50 mm slump , the required water content may be increased or decreased by about 3 percent for each increase or decrease of 25 mm slump. Hence estimated water content for 120 mm slump = 186 + ( 186 X 8.4 percent) = 202 kg/cum

Super plasticisers

As per clause number 6.2.4 , page no 7 of IS 10262: 2019, Polycarbonate ether based super plasticisers reduce water content by 30 percent or above at appropriate dosages. Water content with using appropriate dosages of super plasticisers =202 X 0.7 =141.4 kg/cum

water – cementitious material ratio (w/cm ratio)

As As per table 8 , page no 9 of IS 10262 : 2019 , for target compressive strength at 28 days of 80 N / mm2 , water – cementitious material ratio for 20 mm nominal maximum size aggregate is 0.29. The revised w/cm (+ or – 10 percent) may be established on the basis of experience

Revised w/cm =00.26
Silica fume = 5 percent
Fly ash = 15 percent

Hence revised ( Cement and fly ash or other cementitious material ) content = 141/0.26 = 542 kg /cum

Silica fume quantities per cum for high strength concrete of M70

Silica fume = 542 X 0.05 = 27 kg/cum
Volume of silica fume = ( Mass of silica fume /( Specific gravity of silica fume X1000) = 27/(2.2X1000) = 0.0123

Fly ash quantities per cum

Fly ash = 542 X 0.15 = 81 kg / cum
Volume of Fly ash = ( Mass of fly ash /( Specific gravity of fly ash X1000) = 81/(2.2X1000) = 0.037 cum

Cement quantities per cum

Cement = 542-27-81 = 434 kg/cum
which is less than maximum cement content of 450 kg/cum. Hence OK
Volume of cement = ( Mass of cement /( Specific gravity of cement X1000) = 434/(3.15X1000) = 0.138 cum

Water quantities per cum

Water = 141 kg /cum
Volume of water = ( Mass of water /( Specific gravity of water X1000) = 141/(1X1000) = 0.141 cum

Admixture quantities per cum


Weight of admixture ( assumed 0.5 percent super plasticisers used) = 542 X 0.005 = 2.71 kg/cum
Volume of admixture ( assumed 0.5 percent super plasticisers used )= (2.71) / (1.08 X1000) = 0.0025 cum

Volume of entrapped air

Volume of entrapped air = 0.005 cum

Volume of coarse and fine aggregate

Hence Volume of coarse aggregate and fine aggregate = 1 – (0.0123-0.037-0.138-0.141-0.0025-0.005) = 0.664 cum

Proportion of volume of coarse aggregate and fine aggregate

As per clause number 6.2.7 , Table 10 page number 10 of IS 10262 : 2019 . For Zone II 20 mm nominal maximum size aggregate, Volume of coarse aggregate and fine aggregate = 0.66 per unit volume . Hence volume of fine aggregate = 1 – 0.66 = 0.34 per unit volume of total aggregate . ( for pumpable mixes 10 % coarse aggregate should be decreased and the same percentage of fine aggregate is to be increased)

Coarse aggregate quantities per cum

Volume of coarse aggregate = 0.664 X 0.66 = 0.438 cum
Weight of coarse aggregate = 0.438 X 2.74 X1000 = 1200.00 kg/cum

Fine aggregate quantities per cum


Volume of fine aggregate = 0.664 X0.34 = 0.226 cum
Weight of Fine aggregate = 0.226 X 2.65 X 1000 = 599.00 kg/ cum

concrete

First trial

Cement : 434 kg/cum
Fly ash : 81 kg / cum
Silica fume : 27 kg/cum
Water : 141 kg / cum
Fine aggregate :599 kg/ cum
Coarse aggregate :1200 kg/cum
Chemical admixture : 2.71 kg/cum
W/cm : 00.26

  • cement OPC 53 Grade : 434 kg/ cum = 8.68X 490.00 =Rs. 4253.00
  • Water  : 141 kg / cum = Free of cost = 0.00
  • Fine aggregate  :599 kg/ cum= 0.226 Cum X 2700.00 = Rs. 610.00
  • FLY ASH : 81 kg/cum =81 kg X Rs. 8.00 per kg =Rs. 648.00
  • Silica fume : 27 kg/cum X Rs 20.00 per kg = Rs 540.00
  • Coarse aggregate  :1200 kg/cum = 0.438 cum X 2700.00 = Rs. 1183.00
  • Super-plasticizer (Polycarboxylate ether based) : 2.71 kg /CUM @ Rs 125.00 per kg = Rs. 339.00
  1. Cost of high strength concrete of m70 with admixture (Approx) = Rs. 7573.00

Note : 1. Two more trials having variation of + or – 10 percent of water – cementitious material ratio shall be carried out and a graph between these water cementitious materials ratios and their corresponding strengths shall be plotted to work out the mix proportions for the given target strength for field trials . Considering the durability requirements too. 2. Aggregate shall be used in saturated surface dry conditions if otherwise , when computing the requirements of mixing water , allowances shall be made for the free surface moisture contributed by the fine and coarse aggregate. And if the aggregate is dry the amount of mixing water shall be increased by an amount equal to the moisture likely to be absorbed by the aggregate