Test: Highway Materials & Testing- 2

As per IS 2386 part 4, the steel balls are used as the charge for the test. They are of 48 mm diameter and each ball weighs around 416.67 g. Depending on the grading used for the test, the number of balls used changes.

Angularity number is obtained using the formula, 

Where W represents the mean weight of aggregate (g),
C represents the volume of the cylinder (g) and,
Ga represents the specific gravity
From the readings, mean value, 


The angularity number is represented as a whole number and is rounded off to nearest one.

The tests to determine the stripping value can be classified into six types. They are static immersion test, dynamic immersion test, chemical immersion test, immersion mechanical test, immersion trafficking test and coating test.

To conduct the soundness test, the aggregates are subjected to solutions of sodium sulphate or magnesium sulphate as per IS 2386. After cycles of immersion and drying, the loss in weight of aggregate is noted down in percentage and that gives the soundness result.

Combined index is obtained as the sum of both flakiness and elongation index. The sample is first subjected to flakiness test, then the non-flaky particles are subjected to the elongation test. Their indices are found out and added together.

Dorry abrasion test was used way back and is not used these days. The charge used for the test was sand. It was let into the machine to cause abrasive action. Crushed gravel cannot be used as it is the same material and it would cause attrition, not abrasion.

The sample after removing from the abrasion machine is passed through 1.7 mm sieve and the weight is noted down. 2.36 mm is used in the impact and crushing test on aggregates.

The aggregate impact value is obtained as the ratio of the weight of sample passing 2.36 mm sieve to the weight of the sample taken for the test. For the readings in the question, the aggregate impact value can be found out as

and is expressed as a whole number in percentage.

As per IS 2386 part 3, in the impact test, the sample is filled in three layers and given 25 tamping each. As per IS 2386 part 1, the sample is filled in three layers and tamped 100 times each for the angularity number. As per IS 2386 part 3, in the bulk density test, the sample is filled in three layers and given 25 tamping each. As per IS 2386 part4, the sample for crushing test is filled in three layers and tamped 25 times each.

There are two stages conducted for this test. The sample is polished in the first stage and subjected to pendulum type friction tester in the second stage. The result obtained is the skid number and the mean of two values of the same is taken as the polished stone value.