Types of Test on Stones; Crushing strength test
Types of test on stones, there are five types in this list to ascertain the required properties of stones, the following tests can be conducted (Crushing strength test):
1.Crushing strength test
- Water absorption test
- Abrasion test
- Let us describe all the above types.
- Types of testes on stones, Crushing Strength Test For conducting this test, a specimen of size 40 × 40 × 40 mm is prepared from parent stone. Then the sides are finely dressed and placed in water for 3 days (Crushing strength test).
- The specimen is provided with a layer of plaster of Paris on its top, and bottom surfaces to get an even surface so that load applied is distributed uniformly in the material Crushing strength test).
- this type of load distribution can be obtained satisfactorily by providing a pair of 5 mm thick plywood instead of using plaster of Paris layer also.
- This specimen so placed in the compression testing machine is loaded at the rate of 14 N/mm2 per minute. The crushing load is noted Crushing strength test).
- The crushing strength is equal to the crushing load divided by the area over which the load is applied. And least three specimens should be tested, and the average should be taken as a crushing strength test).
Water Absorption Test
- This water Absorption Test For this test cube specimen weighing about 50 grams prepared and the test is carried out in the steps are given below:
- Note the weight of the dry specimen as W1.
- Place the specimen in water for 24 hours
- Take out the specimen from the machine, wipe out the surface with a piece of cloth, and weigh the specimen. Let its weight be W2.
- Now Suspend the specimen freely in water and weight it. Let its weight be W3.
- Place the specimen in boiling water for 5 hours. After taking it out, wipe the surface with a cloth and weigh it the specimen. Let this weight be W4. Then Crushing strength test),
Brownstones are used as aggregates for road construction.
- The test result was indicating the suitability of stones against the grinding action under traffic. Anyone of the following tests may be conducted to find out the suitability of aggregates:
- Los Angeles abrasion test
- Deval abrasion test
- Dory’s abrasion test.
- However, The Los Angeles abrasion test is preferred since these test results are having a good correlation with the performance of the pavements.
- The Los Angeles apparatus consists of a hollow cylinder 0.7 m inside diameter and 0.5 m long with both ends closed. It is mounted on a frame so that it can be rotated about the horizontal axis in this method.
- IS code has standardized the Los Angeles test procedure for different gradation of specimens. This specified weight of specimen a specified number of cast iron balls of 48 mm diameter is placed in the cylinder in this machine.
- The cylinder is rotated at a speed of 30 – 33 rpm for a specified number of times (500 – 1000).
- The aggregate is removed and sieved on 1.7 mm in IS sieve. Now the weight of aggregate passing is found, and next to Los Angeles value is found as
=Weight of aggregate passing through sieve/
Original weight × 100
- The following value is recommended for the road works only: (For bituminous mixes is 30% For the base course to 50%.)
- Impact Test is the resistance of stones to impact is found by conducting tests in impacting testing machine It consists of a frame with guides in which a metal hammer weighing 13.5 – 15 kg can freely fall from a height of 380 mm.
- Aggregates of size 10 mm to 12.5 mm are filled in a cylinder in 3 equal layers; each layer being tamped 25 times. The same is then transferred to the cup and again tamped 25 times.
- This Hammer is then allowed to fall freely on the specimen 15 times. The specimen is after sieved through a 2.36 mm IS sieve.
- for bituminous McAdam >/ 35%
- for water-bound McAdam >/ 40%
- An acid test is normally carried out on sandstones to check the presence of calcium carbonate, which weakens the weather resisting quality.
- In this test, a sample of stone weighing about 50 to 100 gm is taken and kept in a solution of one percent hydrochloride acid for seven days. The solution is agitated at intervals.
- These good building stone maintains its sharp edges and keeps its surface intact. In case edges are broken and powder is formed on the surface, it indicates the presence of calcium carbonate. Such stones will have poor weather resistance.