Aggregates used in the construction, should be strong enough to resist crushing. If the aggregates are weak, the stability of the structure is likely to be adversely affected. The strength of coarse aggregates is assessed by aggregate crushing test. The aggregate crushing value provides a relative measure of resistance to crushing under gradually applied compressive load. Lesser the aggregate crushing value stronger is the given sample of aggregates.
Object: To determine aggregate crushing value by compressive testing machine.
1. Steel cylinder open with both ends
2. Steel tamping rod
3. UTM (Universal Testing Machine)
4. Cylindrical measure and plunger
5. IS sieves of sizes- 12.5mm and 10mm
1)The aggregates are sieved using 12.5 mm IS sieve and those retained on 10 mm IS sieve are taken and oven dried at 100-110 Celsius for 3-4 hrs.
2)The cylindrical apparatus is then filled with coarse aggregate in 3 layers and each layer tamped 25 times such that there are minimum voids occupied.
3)The weight of the aggregates is then weighed (Wt. A)
4)The top layer is leveled and the plunger is inserted.
5)The whole set up is then kept in the UTM and the compressive loading is done at a uniform rate such that 40 tons is achieved in 10 minutes.
6)The cylinder is taken out and the crushed aggregates are sieved through IS sieve 2.36 mm and the weight of aggregates passing through this sieve is weighed “Weight B”.
Calculations: Aggregate Crushing Value = (B/A) * 100 %
* The value is higher when more percentage of aggregates crush and break into smaller pieces which indicates the aggregates are of a lower quality.
* Aggregate crushing value < 45% for aggregates used for concrete for non wearing surfaces and <25% for wearing surfaces like runways and roadways.