The table below shows the grain size distribution for two aggregates and the spe

Question

The table below shows the grain size distribution for two aggregates and the specification limits for an asphalt concrete. Determine the blend proportion required to meet the specification limits. Report these blend percentages (% stockpile A and % stockpile B) and show your blended gradation in a table. You do not need to show all calculations, but do show an example calculation using the #4 sieve Determine the Fineness Modulus, Absorption, dry specific gravity, and SSD specific gravity of the blended stockpiles

Explanation / Answer

a) Blend proportion is calculated for each aggregate using the following formula-

Blend= % passing x percent aggregate proportion

Total blend = % blend of aggregate A + % blend of aggregate B.

Let us consider 50-50 proportion of aggregate.

sample calculation for #4 sieve,

% Blend of A = 20 x 0.50 = 10

% Blend of B = 85 x .5 = 42.5

Total % Blend = 10+ 42.5 = 52.5

But it is not within the specification limits of 70-50 so change the proportion.

consider 75-25 proportion of A and B respectively.

So total % blend = 20 x 0.75 + 85 x 0.25 = 36.25 .This is not within proportion limit.

So change proportion to 25-75 so

total % blend = 20 x .25 + 85 x .75 = 68.75.

so its within specification limits of 70 - 50.

So total blend of all aggregate in 25-75 proportions to be calculated and checked whether its within specification limits

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