Question

In an aggregate mix, the proportions of coarse aggregate, fine aggregate and mineral filter are 55%, 40% and 5%, respectively. The values of bulk specific gravity of the coarse aggregate, fine aggregate and mineral filler are 2.55, 2.65 and 2.70, respectively. The bulk specific gravity of the aggregate mix (round off to two decimal places) is _____

Answer 1

Concept:

Theoretical Specific gravity or apparent specific gravity:

It is the specific gravity without considering air voids is given as

 \({G_t} = \frac{{{W_1} + {W_2} + {W_3} + {W_4}}}{{\frac{{{W_1}}}{{{G_1}}} + \frac{{{W_2}}}{{{G_2}}} + \frac{{{W_3}}}{{{G_3}}} + \frac{{{W_4}}}{{{G_4}}}}}\)

If weight of constituents are given in percent of total mix, then

 \({G_t} = \frac{{100}}{{\frac{{{W_1}(\% )}}{{{G_1}}} + \frac{{{W_2}(\% )}}{{{G_2}}} + \frac{{{W_3}(\% )}}{{{G_3}}} + \frac{{{W_4}(\% )}}{{{G_4}}}}}\)

Calculation:

Given,

Proportions of coarse aggregate (W₁%) = 55%

Proportions of fine aggregate (W₂%) = 40%

Proportions of mineral filler (W₃%) = 5%

G₁ = 2.55, G₂ = 2.65, G₃ = 2.70

Theoretical specific gravity is given by, \({G_t} = \frac{{100}}{{\frac{{{W_1}(\% )}}{{{G_1}}} + \frac{{{W_2}(\% )}}{{{G_2}}} + \frac{{{W_3}(\% )}}{{{G_3}}}}}\)

 \({G_t} = \frac{{100}}{{\frac{{55}}{{2.55}} + \frac{{40}}{{2.65}} + \frac{5}{{2.70}}}}\)

G_t = 2.60