Challenge

Project on Concrete Mix Design for various grades of Concrete

PPulugurtha Sri Sai Bharghav15 Sept 2021

calculation of concrete mix design for M35 grade concrete with Fly ash:

. Data collection

grade designation = M35
Type of cement = OPC 43 grade conforming to Is 8112
Max nominal size of aggregate = 20mm
max w/c ratio = 0.45
workability = 100mm
exposure condition = severe
method of concrete placing = pumping
Degree of supervision = good
Type of aggregate = crushed angular aggregate
max cement content = 450 kg/m3
chemical admixture = super plasticizer.

specific gravity of cement = 3.15
specific gravity of flyash = 2.2
water absortion of coarse aggregate = 0.5%
water absorption of fine aggregate = 1.0%
specific gravity of coarse aggregate = 2.74
specific gravity of fine aggregate = 2.74
free surface moisture for coarse and fine aggregate is Nil because it is used in dry condition not wet condition

1- target mean strength for mix proportion’s

F'ck = Fck +1.65 S where S= 5 N/mm2

= 35+ 1.65*5= 42.5 N/mm2

2- Selection of w/c ratio

From the table 5 of Is 10262:2009 for sever condition exposure

max w/c ratio = 0.45

based on experience adopted w/c ratio is 0.38

0.38>0.45 hence ok

3- Selection of water content:

from table 2 IS 10262:2009 max water content for 20mm aggregate = 186 lit

estimated water content for 100mm slump is

= 186 + 6/100*186

= 197 lit

As super plastizers is used the water content can be reduced upto 20% and above based on trails water content reduction of 29% is achieved with plasticizers.

Hence the arrived water content = 197*0.71= 140 lit

4- Calculation of cement content:

w/c ratio = 0.38

cementitious material (cement + flyash / content)

= 140/0.38 = 368.42 kg/m3

From table 5 of IS 456 min cement content for sever exposed condition is 320 kg/m3

so 368.42 > 320 Hence ok

now to prapottinate a mix containing fly ash the following steps are suggested

a) The percentage of flyash needs to be decided based on project requirements and quality of materials

b) In dome cases incerase in cementitious material can be warented incerase in cementitious materialcontent and its percentage is based on its experience and trail

cementitious material incerased by 10%

= 368.42 * 1.10 = 405.26 kg/m3

water content = 140 lit

so w/c ratio = 140/405.26= 0.34

flyash @ 30% total cementitious material content = 405.26*30%= 121.57 Kg/m3

cement opc = 405.26-121.57= 283.69 kg/m3

saving cement while using fly ash= 405.26-283.69= 121.57 kg/m3

5- praportion of volume of coarse and fine aggregate:

from table 3 IS 10262:2009 volume of coarse aggregate corresponding to 20mm size aggregate and fine aggregate for w/c is 0.6

In the present case the w/c is 0.38

therefore the volume of coarse aggregates needs to be increased to decrease the fine aggregate content

As w/c ratio is lower by 0.10 the praportion od volume of coarse aggregate is incerased by 0.02

Corrected volume of coarse aggregate for the w/c ratio of 0.39 = 0.39+0.12= 0.51

for pumpable concrete these values are reduced by 10%

volume of coarse aggregate = 0.62*0.9= 0.56

volume of fine aggragate = 1- 0.56 = 0.44

6- mix calculations:

The mix calculations per unit volume of concrete shall be as follows

volume of concrete= 1m3
volume of cement = 283.69/3.15*1/1000= 0.090 m3
volume of flyash = 121.57/2.2*1/1000= 0.055 m3
volume of water = 140/1*1/1000 = 0.140 m3
volume of chemical admixtures = 7.61 / 1.145 * 1/1000= 0.06 m3
volume of aggregate (ca & fa )= (1-0.090+0.140+0.006)= 0.709m3
mass of coarse aggregate = 0.709*0.56*2.74*1000= 1087.88 kg/m3
mass of fine aggregate = 0.709*0.44*2.74*1000= 854 kg/m3

7- mix praportions for trail numbers

cement= 283.69 kg/m3
flyash = 121.57 kg/m3
water = 140 kg/m3
fine aggregate = 854 kg/m3
coarse aggregate = 1087.88 kg/m3
chemical admixture = 7 kg/m3
w/c ratio = 0.38
Trail mix ratio = 283.69:854:1087.88
= 1: 3.0: 3.83.

calculation of concrete mix design for M50 grade concrete without Fly ash: