Question

A Marshall specimen is prepared for bituminous concrete with a bitumen content of 5% by weight of total mix. The theoretical and the measured unit weights of the mix are $2.442gm/c{m}^3$ and $2.345gm/c{m}^3$, respectively. The bitumen has a specific gravity of 1.02. The percent voids in mineral aggregate filled with bitumen (VFB) are

• A. 73.55
• B. 34.55
• C. 74.3
• D. 35.9

Answer 1

The correct option is C 74.3

Theoretical unit weight,
$G_t=2.442g/c{m}^3$

Measured unit weight,
$G_m=2.345g/c{m}^3$

Percent air voids
$=\frac{G_t-G_m}{G_t}$
$=\frac{2.442-2.345}{2.442}\times 100$
$=3.972\text{\% of the total volume of sample}$

Assuming the weight of sample = 100 g
$\Rightarrow$ Volume,
$V=\frac{100}{2.345}=42.644c{m}^2$

Volume of air voids,
$V_a=3.972\text{\% of V}$
$V_a=\frac{3.972}{100}\times 42.644=1.694c{m}^3$

Volume of bitumen,
$V_b=\frac{5}{1.02}=4.902c{m}^3$

Void filled with bitumen
$=\frac{V_b}{V_a+V_b}=\frac{4.902}{1.694+4.902}$
$=0.7432=74.3\%$