Question

1. How does the toughness of road aggregates differ from their compressive strength? Can you write a mathematical relationship, if any?
2. A test group of the class used an old aggregate impact test machine. The weight of the hammer was about 1 kgf lower than the standard weight. Determine the percentage error in the impact value of the aggregate.
3. Should a poor quality road aggregate give a low impact value? Justify your answer.

Answer 1

Compressive strength is the resistance against gradual loading and it is determined by aggregates crushing value test but Toughnessis the resistance againest the impact loading.

There is no mathematical formula to determine compressive strength or toughness. But there is a test to determine Aggregates crushing value for compressive strength and aggregates imact value for toughness.

These are determined by the ratio of weight of residue aggregates after passing over a standard sieve to the weight of initial aggregates.

There is no mathematical formula to calculate impact value by using hammer weight however we can compare by using energy transfer by hammer to the aggregates.

standard weight of hammer = W1 = 14 kgf

now using weight of hammer = W2 = 13 kgf

Potential energy PE = W*h

h = height of fall = constant for both

hence PE is directly proportional to weight

or error 7.14 %

If we use poor quality of aggregates then we get high impact value because more aggregates is deformed under standard weight of hammer ans height of fall,

Aggregate Impact value is determined by the ratio of weight of residue aggregates after passing over a standard sieve to the weight of initial aggregates.

If poor quality of aggregates then more aggregates is residue at the end of test.

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