DETERMINATION OF STRIPPING VALUE OF ROAD AGGREGATES
IS: 2386 - Part 4
Some types of aggregates have lesser affinity towards bitumen than water. The phenomenon of stripping is observed when the pavement layer is subjected to prolonged soaking under water. In the state of Kerala where long periods of rain prevail, this property of the aggregate is very relevant. Hence to assess the suitability of aggregates for bituminous construction, the stripping characteristics of the binder from the aggregates by water is determined by various tests. Several anti-stripping agents are available in the market which when added to the bituminous mix is found to reduce stripping. The procedure for determining stripping value of road aggregates with bitumen or tar binders by static immersion method is explained below.
(i) Thermostatically controlled water bath.
(ii) Oven to heat aggregate.
(iii) Sieves of sizes 20 mm and 12.5 mm.
(iv) Beaker of 500 ml capacity.
(v) Mixer to mix aggregate and bitumen.
a) Take 200 gm of clean and dry aggregate passing 20 mm IS sieve and retained on 12.5 mm sieve in a mixer or heating pan.
b) The dried, clean aggregates are heated up to 150°C and mixed with bitumen binder amounting to 5% by weight of aggregate heated to 160°C.
c) The aggregate and binder are mixed thoroughly till they are completely coated and mixture is transferred to the beaker.
d) The mix is then allowed to cool at room temperature for about 2 hours.
e) Distilled water is then added to immerse the coated aggregates. The beaker is covered and kept in a water bath maintained at 40°C.
f) After 24 hours, the beaker is taken out and the extent of stripping is visually estimated while the specimen is still immersed in water.
a) The stripping value of the aggregate is the area bitumen stripped measured by visual observation expressed as a % of the total surface area of the sample mix.
b) A comparison, of aggregates with bitumen coating stripped off and remaining intact, can made from the figures (1) and (2) given above. Stripping Value = Uncovered area observed visually Total area of the aggregates (100%)
The mean of the three results shall be reported as stripping value of the tested material and shall be expressed to the nearest whole number.