Question

The approximate ratio of the strength of cement concrete at 7 days to that at 28 days is

1. 0.45
2. 0.60
3. 0.87
4. 1.15

Answer 1

Correct Answer - Option 2 : 0.60

Concept:

Characteristic compressive strength(f_ck):

28 days compressive strength is the characteristic compressive strength (fck) of concrete when a cube of standard size of 150 mm is tested in compressions testing machine after 28 days from casting.

Tensile strength of concrete = 10% of compressive strength

Bending strength of concrete = 15% of compressive strength

Shear strength of concrete = 20% of compressive strength

Days	Strength of concrete
3	\(\frac{1}{2}\)× Fck
7	\(\frac{2}{3}\)× Fck
14	0.9 Fck
28	Fck

Hence, the most appropriate option would be ‘0.60’.