To determine the stripping value of the given aggregate sample by static immersion method.

STATIC IMMERSION TEST

(AASHTO T 182, ASTM D 3625)

OBJECT: TO DETERMINE THE STRIPPING VALUE OF THE GIVEN AGGREGATE SAMPLE BY STATIC IMMERSION METHOD

PERFORMANCE OBJECTIVE:

Upon successful completion of this lab experiment, the student will able to:

Determine the stripping value of the aggregates by static immersion method that is the stripping of the coated binder from the aggregate due to the presence of water.

EQUIPMENT:

1) Thermostatically controlled oven. 2) Water bath 3) Beaker 4) Mixer

DISCUSSION:

Stripping Value:

It is the ratio of the uncovered area observed visually to the total area of aggregates in each test expressed in percentage.

Bitumen and tar adhere well to all normal types of aggregates provided they are dry and are not exceptionally dusty. In the absence or water, there is practically no adhesion problem in bituminous road construction. Two problems are observed due to the presence of water.

First, if the aggregate is wet and cold, it is normally not possible to coat it with a bituminous binder. The problem can be dealt with by removing the water film on the aggregate by drying and by increasing the mixing temperature.

The second problem is the stripping of the coated binder from the aggregate due to the presence of water. This problem of stripping is experienced only with bituminous mixtures which are permeable to water.

PROCEDURE:

I. Take 200g of dry and clean aggregates by passing a 19 mm sieve and retained on a 12.5 mm sieve.

1. Heat them to 150⁰C when these are to be mixed with bitumen and the aggregates are heated up to 100⁰C when these are to be mixed with tar.
   
2. Take Five percent by weight of the bitumen binder and heat it for 160⁰C (100⁰C in the case of tar biI1der).
   
3. Mix thoroughly aggregate and binder till they are completely coated transfer the mixer to a 500ml beaker and allow it to cool at room temperature for about two hours.
   
4. Add distilled water to immerse the coated aggregates.
   
5. Cover the beaker and keep it in a water bath by maintaining a temperature of 40°C.
   

(Take care that the level of water in the water bath is at least half the height of the beaker.)

1. After 24 hours take out the beaker and cool at room temperature and the extent of stripping is estimated visually while the specimen is still under water.
   

Note:

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 to the nearest 5 percent.

APPLICATIONS:

Some types of aggregates have lesser affinity with bitumen in comparison with water and hence stripping of the bituminous binder occurs when the mix is immersed in water. Thus an adhesion test such as the simple static immersion test or the stripping test would be suitable to assess whether the binder would adhere to the aggregates when immersed in water. Indian Roads Congress (IRC) has specified the maximum stripping value as 25 percent for aggregates to be used in bituminous construction like surface dressing penetration macadam, bituminous macadam, and carpet.

RESULT:

COMMENTS:

Aggregates Immersed in solution Aggregates outside solution