Tests on Stones
To determine the required properties of stones, the following tests Could be conducted:
(a) Crushing Strength Test
(b) Water Absorption Test
(c) Abrasion Test
(d) Impact Test
(e) Acid Test
Crushing Strength Test of Stone
For conducting this test, a specimen of size 40 × 40 × 40 mm is prepared from parent stone. Afterward, the sides are finely dressed and placed in water for three days. The saturated specimen is provided with a layer of plaster of paris on its top also bottom surfaces to get even surface so that load applied is distributed uniformly.
Uniform load distribution could be obtained satisfactorily by providing a pair of 5 mm thick plywood instead of using plaster of paris layer also. The specimen so placed in the compression testing machine is loaded in the rate of 14 N/mm2 per minute. The crushing load is noted.
Then crushing strength is equal to this crushing load divided by the area where the load is applied. At least three specimens must be tested, and the average ought to be taken as crushing strength.66
Water Absorption Test of Stone
With this test cube specimen weighing about 50 grams are Ready, and the test is carried out at the steps given below:
• Note the weight of dry specimens as W1.
• Place the specimen in water for 24 hours.
• Take out the specimen, wipe out the surface with a piece of cloth, and weigh the specimen. Let its weight be W2.
• Suspend the specimen freely in weight and water it. Let its weight be W3.
• Place the specimen in boiling water for 5 hours. Then take it out, wipe the surface with a cloth, and weigh it. Let this weight be W4. Then,
Percentage absorption by weight = (W2 – W1) / W1 x 100 ……….(1)
Percentage absorption by volume = (W2 – W1) / (W2 – W3) x 100 ……….(2)
Percentage porosity by volume = (W4 – W1) / (W2 – W3) x 100 ……….(3)
Density = W1 / (W2 – W1) x 100 ……….(4)
Specific Gravity = W1 / (W2 – W3) x 100 ……….(5)
Saturation Coefficient = Water Absorption / Total Porosity = (W2 – W1) / (W4 – W1)
Abrasion Test of Stone
This test is carried out on stones that are used as aggregates for road construction. The test result indicates the suitability of stones against the grinding action under traffic.
Anyone of the following tests could be conducted to find out the suitability of aggregates:
(1) Los Angeles Abrasion Test
(2) Deval Abrasion Test
(3) Dorry’s Abrasion Test.
However, the Los Angeles abrasion test is preferred since these test results have a good correlation with the performance of the pavements.
The Los Angeles apparatus [Below Figure] consists of a hollow cylinder 0.7 m inside diameter and 0.5 m long with both ends closed. It is mounted onto a frame so that it could be rotated about a horizontal axis. IS code has standardized the test procedure for different gradations of specimens.
Together with the specified weight of the specimen, a specified number of cast iron balls of 48 mm diameter are placed in the cylinder.
Los Angeles Testing Machine
Then the cylinder is rotated at a speed of 30 to 33 rpm for a specified number of times (500 to 1000). Then the aggregate is removed along with sieved on 1.7 mm. IS sieve. The weight of aggregate passing is found.
Then Los Angeles value is found as = (Weight of aggregate passing through sieve / Original weight ) x 100
The following values are recommended for road works:
| For bituminous mixes | 30% |
| For base course | 50% |
Impact Test of Stone
The resistance of stones to impact is found by conducting tests in impacting the testing machine [Below Figure]. It consists of a frame with guides where a metal hammer weighing 13.5 to 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, every layer being tamped 25 times. The same is then transferred into the cup and again tamped 25 times. The hammer is then allowed to fall freely onto the specimen 15 times.
The specimen is then sieved through a 2.36 mm sieve.
Then, Impact value = W2 / W1
where,
W2 = Weight of Fines.
W1 = Original Weight.
The recommended impact values for various works are:
(a) for wearing course ≯ 30%
(b) for bituminous macadam ≯ 35%
(c) for water-bound macadam ≯ 40%
Acid Test of Stone
This 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 hydrochloric acid for seven days.
The solution is agitated at intervals. A good building stone maintains its sharp edges and keeps its surface intact. If edges are broken, and powder is formed on the surface, it indicates the presence of calcium carbonate. Such stones will have poor weather resistance.
FAQ: Stone Testing Methods
What are the primary tests conducted on stones to determine their suitability?
The primary tests include Crushing Strength Test, Water Absorption Test, Abrasion Test (such as the Los Angeles Abrasion Test), Impact Test, and Acid Test.
How is the Crushing Strength Test performed?
A specimen of stone is prepared, saturated with water, and placed in a compression testing machine. The crushing load is applied at a uniform rate, and the crushing strength is calculated as the load divided by the area of application.
What does the Water Absorption Test reveal about stones?
This test assesses the amount of water absorbed by the stone, which helps determine its porosity and density. It involves soaking the stone specimen, measuring weight changes, and calculating parameters like percentage absorption and specific gravity.
Which abrasion test is commonly used to evaluate stones for road construction?
The Los Angeles Abrasion Test is preferred due to its correlation with pavement performance. It involves subjecting stone aggregates to abrasive forces in a rotating cylinder and measuring the weight loss.
How is the Impact Test conducted on stones?
Stones are tested for their resistance to impact using a testing machine where a hammer falls onto the specimen. The impact value is determined by measuring the weight of fines produced relative to the original weight of the stone.
Why is the Acid Test performed on stones?
The Acid Test helps assess the presence of calcium carbonate in stones like sandstone, which affects their weather resistance. Stones that react by forming powder or losing sharp edges indicate poor weathering quality.
How many specimens are typically tested for each stone property?
For reliable results, at least three specimens are tested for properties such as crushing strength and water absorption. The average of these tests is considered for assessment.
What are the recommended values from these tests for various construction applications?
Recommended values, such as crushing strength for different types of stone or impact values for specific construction works like wearing courses or macadam, are provided based on industry standards and requirements.
How are the results of these tests used in practice?
The results guide engineers, architects, and construction professionals in selecting stones suitable for specific applications, ensuring durability, safety, and performance in various environmental conditions.
What are the standard procedures and guidelines for conducting these tests?
The Indian Standard (IS) codes and other international standards prescribe detailed procedures and guidelines for conducting each test, ensuring consistency and reliability in the results obtained.
