Question

The approximate ratio between the strength of cement concrete at 7 days and 28 days is

• A. $\frac{1}{3}$
• B. $\frac{1}{2}$
• C. $\frac{2}{3}$
• D. $\frac{3}{4}$

Answer 1

The correct option is C $\frac{2}{3}$

Age of cement	Age factor for low strength concrete
7 days	0.65 - 0.7
1 month	1.0
3 months	1.1
12 months	1.2

$\frac{\text{Strength of concrete at 7 days}}{\text{Strength of concrete at 28 days}}=0.67=\frac{2}{3}$