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Stripping value Test of Road Aggregate

 What is Stripping value of Road Aggregate ?

This test is conducted to determine the effects of moisture upon the adhesion of the bituminous film to the surface particles of the aggregate. This test is of significant value to ascertain the suitability of the two materials viz. bitumen (binder) and aggregates, because one particular aggregate may be satisfied with one binder and unsatisfactory with another; and the same being true for the binders. The static immersion method is also used to determine the stripping value.

Objectives

  • To determine the stripping value of aggregates used in road construction;
  • To ascertain the suitability of road aggregates for bituminous road construction.

Apparatus

  • Thermostatically controlled water bath.
  • Beakers of capacity 500 ml.

Procedure

The aggregate sample: the test sample consists of aggregate of size passing 25 mm sieve and retained on 12.5 mm sieve.

  • Obtain the material that passes through 25 mm sieve and is retained on 12.5 mm sieve.
  • Dry, clean and heat the binder and aggregates to 150-175 oC and 120-150 oC respectively and mix with 5 per cent binder by weight of aggregate.
  • After complete coating, allow the mixture to cool at room temperature in clean dry beaker.
  • Add distilled water to immerse the coated aggregates.
  • Cover the beaker and keep it undisturbed in a thermostatic water bath at a temperature of 40 oC for a period of 24 hours.
  • Estimate the extent of stripping by visual examination while the specimen is still under water and express as the average per cent area of aggregate surface uncoated.

Note: Three samples may be tested simultaneously so as to arrive at an average value. The stripping value is expressed to the nearest whole number.

Precautions

  • The aggregates should be thoroughly dried before mixing wih binder.
  • Distilled water should be used for the test.
  • Mix-up of the two separate samples should be uniform.

Record of Observations

  Sample 1 Sample 2 Sample 3
Percentage of Area of aggregate uncoated by immersion in water % % %
Average stripping value =                            %      

Interpretation of Results

The result of the stripping test give an indication regarding susceptibility of aggregates to the action of water, or moisture. The more the stripping value, the poorer are the aggregates from point of view of adhesion. IRC has specified the maximum stripping value of 25% for aggregates to be used in bituminous road construction.

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