Stripping Value Test On Road Aggregates

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What is Stripping Value Test?

The stripping value of aggregates is determined as the ratio of the uncovered area observed visually to the total area of aggregates, expressed as a percentage. Bitumen and tar adhere well to all normal types of aggregates provided they are dry and are not exceptionally dusty. This problem of stripping is experienced only with bituminous mixtures, which are permeable to water. This test gives the procedure for determination of the stripping value of aggregates by static immersion method, when bitumen and tar binders are used.

Aim:

To determine the stripping value of road aggregates by binders.

Apparatus Requires for Test:

The apparatus required for this experiment are:

1. Thermostatically controlled water bath.
2. Oven to heat aggregate.
3. Sieves of sizes 20 mm and 12.5 mm.
4. Beaker of 500 ml capacity.
5. Mixer to mix aggregate and bitumen.

Procedure:

1. 200 g of clean and dry aggregate passing 20 mm IS sieve and retained on 12.5 mm sieve are heated up to 150°C when these are to be mixed with bitumen.
2. Bitumen binder amounting to five percent by weight of aggregate is heated to 160°C.
3. The aggregate and binder are mixed thoroughly till they are completely coated and mixture is transferred to the beaker and allowed to cool at room temperature for about 2 hours.
4. Distilled water is then added to immerse the coated aggregates.
5. The beaker is covered and kept in a water bath maintained at 40°C, for 24 hours.
6.  After 24 hours, the beaker is taken out, cooled at room temperature and the extent of stripping is estimated visually while the specimen is still under water.

Result:

The result is reported as the percentage of stone surface that remains coated after the specified periods, the mean value of at least three visually estimated values, being rounded off to the nearest 5 percent. By visual estimation, stripping value of road aggregates is = _______ %

Specifications:

Indian Road Congress (IRC) has specified the maximum stripping value as 5 percent for aggregates to be used in bituminous construction like surface dressing penetration macadam, bituminous macadam and carpet.

Applications of stripping value test:

Some types of aggregates have a lesser affinity with bitumen in comparison with water and hence stripping value of the bituminous binder is done when the mix is immersed in water. The problem of stripping in coated aggregate is not so amenable to theoretical treatment. Thus an adhesion test such as the simple stripping test would be suitable to assess whether the binder would adhere to the aggregate when immersed in water. Several anti-stripping agents are available, which when used with the bituminous mix reduce the stripping.