AGGREGATE CRUSHING VALUE TEST
AIM: To find Aggregate Crushing value of the given aggregate sample.
APPARATUS:
Steel cylinder, cylindrical measure, Steel temping rod, Balance, Compressions testing machine
PROCEDURE:
The aggregate passing 12.5 mm sieve and retained on 10 mm IS sieve is selected for standard test. The aggregate should be in surface dry condition before testing. The aggregate may be dried by heating at a temperature 100o C for a period of 4 hours and is tested after being cooled to room temperature.
The cylindrical measure is filled by the test sample of aggregate in three layers of approximately equal depth, each layer being tamped 25 times by the rounded end of the tamping rod. After the third layer is tamped, the aggregate at the top of the cylindrical measure is leveled off by using the tamping rod as a straight edge. About 6.5 kg of aggregate is required for preparing two test samples. The test sample thus taken is then weighed. The same weight of the sample is taken in the repeat test.
The cylinder of the test apparatus is placed in position on the base plate; one third of the test sample is placed in the cylinder and tamped 25 times by the tamping rod. Similarly, the other two parts of the test specimen are added, each layer being subjected to 25 blows. The total depth of the material in the cylinder after tamping shall however be 10 cm. The surface of the aggregate is leveled and the plunger inserted so that it rests on this surface in level position. The cylinder with the test sample and plunger in position is placed on compression testing machine. Load is then applied through the plunger at a uniform rate of 4 tones per minute until the total load is 40 tones, and then the load is released. Aggregates including the crushed portion are removed from the cylinder and sieved on a 2.36 mm IS sieve. The material which passes this sieve is collected.
The above crushing test is repeated on second sample of the same weight in accordance with above test procedure. Thus two tests are made for the same specimen for taking an average value.
CALCULATION:
Total weight of dry sample taken = W1 gm.
Weight of the portion of crushed material passing 2.36 mm IS sieve = W2 gm Aggregate crushing value = 100 W2 / W1
RESULT:
The mean of the crushing value obtained in the two tests is reported as the aggregate crushing value.
APPLICATIONS OF AGGREGATE CRUSHING TEST
The aggregate crushing value is an indirect measure of crushing strength of the aggregates. Low aggregate crushing value indicates strong aggregates, as the crushed fraction is low. Thus the test can be used to assess the suitability of aggregates with reference to the crushing strength for various types of pavement components. The aggregates used for the surface course of pavements should be strong enough to withstand the high stresses due to wheel loads, including the steel tyres of loaded bullock-carts. However as the stresses at the base and sub- base courses are low aggregates with lesser crushing strength may be used at the lower layers of the pavement.
Indian Roads Congress and ISI have specified that the aggregate crushing value of the coarse aggregates used for cement pavement at surface should not exceed 30 percent. For aggregates used for concrete other than for wearing surfaces, the aggregate crushing value shall not exceed 45 percent, according to the ISS. However aggregate crushing values have not been specified by the IRC for coarse aggregates to be used in bituminous pavement construction methods.
AIM: To find Aggregate Crushing value of the given aggregate sample.
APPARATUS:
Steel cylinder, cylindrical measure, Steel temping rod, Balance, Compressions testing machine
PROCEDURE:
The aggregate passing 12.5 mm sieve and retained on 10 mm IS sieve is selected for standard test. The aggregate should be in surface dry condition before testing. The aggregate may be dried by heating at a temperature 100o C for a period of 4 hours and is tested after being cooled to room temperature.
The cylindrical measure is filled by the test sample of aggregate in three layers of approximately equal depth, each layer being tamped 25 times by the rounded end of the tamping rod. After the third layer is tamped, the aggregate at the top of the cylindrical measure is leveled off by using the tamping rod as a straight edge. About 6.5 kg of aggregate is required for preparing two test samples. The test sample thus taken is then weighed. The same weight of the sample is taken in the repeat test.
The cylinder of the test apparatus is placed in position on the base plate; one third of the test sample is placed in the cylinder and tamped 25 times by the tamping rod. Similarly, the other two parts of the test specimen are added, each layer being subjected to 25 blows. The total depth of the material in the cylinder after tamping shall however be 10 cm. The surface of the aggregate is leveled and the plunger inserted so that it rests on this surface in level position. The cylinder with the test sample and plunger in position is placed on compression testing machine. Load is then applied through the plunger at a uniform rate of 4 tones per minute until the total load is 40 tones, and then the load is released. Aggregates including the crushed portion are removed from the cylinder and sieved on a 2.36 mm IS sieve. The material which passes this sieve is collected.
The above crushing test is repeated on second sample of the same weight in accordance with above test procedure. Thus two tests are made for the same specimen for taking an average value.
CALCULATION:
Total weight of dry sample taken = W1 gm.
Weight of the portion of crushed material passing 2.36 mm IS sieve = W2 gm Aggregate crushing value = 100 W2 / W1
RESULT:
The mean of the crushing value obtained in the two tests is reported as the aggregate crushing value.
APPLICATIONS OF AGGREGATE CRUSHING TEST
The aggregate crushing value is an indirect measure of crushing strength of the aggregates. Low aggregate crushing value indicates strong aggregates, as the crushed fraction is low. Thus the test can be used to assess the suitability of aggregates with reference to the crushing strength for various types of pavement components. The aggregates used for the surface course of pavements should be strong enough to withstand the high stresses due to wheel loads, including the steel tyres of loaded bullock-carts. However as the stresses at the base and sub- base courses are low aggregates with lesser crushing strength may be used at the lower layers of the pavement.
Indian Roads Congress and ISI have specified that the aggregate crushing value of the coarse aggregates used for cement pavement at surface should not exceed 30 percent. For aggregates used for concrete other than for wearing surfaces, the aggregate crushing value shall not exceed 45 percent, according to the ISS. However aggregate crushing values have not been specified by the IRC for coarse aggregates to be used in bituminous pavement construction methods.
