Question

In Marshall method of mix design the coarse aggregate, fine aggregate, fines and bitumen having respective value of G as 2.6, 2.7, 2.65 and 1.01 are mixed in the relative proportions (% by wt) of 55, 35.8, 3.7, and 5.5 respectively. The theoretical sp. gravity of the mix and effective specific gravity of the aggregate in mix respectively are

• A. 2.42 and 2.93
• B. 2.42 and 2.63
• C. 2.64 and 2.78
• D. 2.42 and 2.78

Answer 1

The correct option is B 2.42 and 2.63

Theoretical specific gravity,

$G_t=\frac{w_1+w_2+w_3+w_4}{\frac{w_1}{G_1}+\frac{w_2}{G_2}+\frac{w_3}{G_3}+\frac{w_4}{G_4}}$
$G_t=\frac{100}{\frac{55}{2.6}+\frac{35.8}{2.7}+\frac{3.7}{2.65}+\frac{5.5}{1.01}}$
$=2.424$

Let effective specific gravity of aggregates (coarse + fine )
be G'

$G^{\prime }=\frac{(55\times 2.6)+(35.8\times 2.7)}{55+35.8}$
$=2.639=2.64$