Building Materials, Third Edition

QQT f2w—

—

(iii) Decrease in the value of water-

cement ratio by nil

(0.50–0.40) = 0.10

overall adjustment +1.5 per cent –3.5 per cent

Thus after incorporating the above adjustments the sand content = 35–3.5 = 31.5

and the water content = 186 + 1.5 ×^186

100

= 188.8 lit.

Step 4: Determination of cement contents:

Water-cement ratio = 0.40

Quantity of water after adjustment = 188.8 liters

Therefore, cement content =

1 88. 8

0 .40

= 472 kg

This cement content has now to be checked against the minimum cement content required
for mild exposure condition in reinforced concrete. The minimum cement content specified in
Table 11.1 is 320 kg/m^3 from durability considerations. Therefore the value of 472 kg/m^3 is
acceptable.
Step 5: Now quantities of coarse and fine aggregates are worked out per m^3 of concrete as
given below.
Volume of concrete = 1– 0.02 (entrapped air)
= 0.98 m^3
= 980 litres.

980 = 

472

1 88.8

3.15 0.315 2.66

fa

fa= 537.39 kg

Similarly,

980 = 



472

1 88.8

3.15 (1 0.315) 2.72

Ca

Ca= 1195 kg

Therefore, the mix proportion becomes:

Cement Water Sand Coarse aggregate

472 188.8 537.39 1195

or 1 0.40 1.138 2.531

Adjustments required for water absorption:

Water absorbed by coarse aggregates

=

1195 0.5
 2 5.98 lit

100

0.10

0.05

×(1) = 2.0