Specific gravity and water absorption test are significant tests on aggregates. Perhaps aggregates are the fundamental and essential components of concrete and play a significant role in the design mix of concrete. More than 70 to 80 per cent of the volume of concrete is aggregate. Hence the water absorption and specific gravity test are essential and significant tests .
The specific gravity is the measure of strength of aggregates, while water absorption indicates the porosity of aggregates.
Also Read : Quality tests to be done on Concrete
Also Read : Bitumen – 9 quality tests on bitumen
Tests on Aggregates
Aggregates are the second major ingredient of concrete that contributes around 60 to 70% of its volume. One of the major contributing factors to the concrete quality is the quality of aggregates used therein. The test methods of aggregates are done as per IS 2386 part-4 assists in assessing the quality of aggregates. Following are the tests for analysing the quality of aggregate.
- Aggregate Crushing test
- Abrasion test
- Soundness test on aggregate
- Impact test
- Shape test
- Water absorption test
- Bulk specific gravity test
This article is about Specific Gravity and Water absorption test on Aggregate.
Specific gravity and water absorption test
The specific gravity is an indirect measure of the strength of aggregate. Through this test, the general identification of the aggregate becomes easier. Low specific gravity aggregates are weak. Hence, they are not suitable for construction.
Water absorption of aggregate measures the weather resistance. It is the percentage of water the aggregate absorbs when immersed in water. The test method for specific gravity and water absorption test is as follows.
Relevant IS code for specific gravity and water absorption test
- IS:2386(Part 4)-1963
Apparatus used for specific gravity and water absorption test
- Weighing machine
- Drying oven
- Wire mesh
- Container
Test procedure
- For this test, take about 2000g of aggregate and wash them thoroughly with water.
- Remove the fine particles and dust, then drain the water and place them in the wire basket.
- Then immerse this in distilled water with a temperature between 22 and 32 degree Celsius for 24 hours.
- Then Weigh the basket with aggregates and record them as A1.
- After 24 hours, remove the aggregates from the mesh and weigh them as A2.
- Then drain the water from the aggregate and Again weigh the dried aggregate. B
- Place the sample in the dry oven for 24 hours. after the oven drying weighs them and record as C.
- Now calculate the specific gravity and water absorption of the aggregate using the given formula.
Specific gravity = C / (B- A)
Water absorption = {(B-C)/C} * 100
where, A= A1 – A2, ie weight of the saturated aggregate in water
B = weight of drained aggregate
C = weight of oven-dried aggregate.
Aggregate with high specific gravity has good strength. The normal value of specific gravity is 2.5 to 3.0. The water absorption should not exceed 0.6%. Thus this test helps to determine the quality, strength and water absorption.