Building stones undergo several tests to determine their properties and assess their suitability for various construction purposes. These tests generate information on both physical and chemical properties, as well as strength and hardness characteristics. By subjecting building stones to these tests, engineers and architects can gather essential data that helps them make informed decisions about which stones to use for different construction projects.
Tests on Building Stones
There are various tests available to evaluate the properties of building stones. One of these is the acid test, which involves applying an acid to the surface of the stone to determine its chemical composition. Another test is the attrition test, which measures the resistance of the stone to wear and tear.
The crushing test is another way to assess the strength of the stone by subjecting it to a compressive load. Crystalline test determines the percentage of crystalline substances present in the stone. The freezing and thawing test examines the resistance of the stone to changes in temperature.
The hardness test is used to determine the scratch resistance of the stone while the impact test assesses its resistance to sudden forces or impacts. The water absorption test measures the amount of water absorbed by the stone over a specific period of time.
Microscopic testing can also be carried out to examine the internal structure of the stone. Lastly, Smith’s test is a type of impact test that is commonly used to determine the toughness and durability of stones. These tests provide valuable information about the quality and durability of building stones and help in selecting the most suitable material for construction purposes.
Acid Test on Building Stone
To determine the presence of calcium carbonate in building stone, a test is conducted using a sample of stone weighing approximately 50 to 100 grams. The sample is placed in a solution of hydrophobic acid with a strength of one percent and is left for a duration of seven days. During this period, the solution is agitated at intervals.
After the seven-day period, the state of the stone is examined to evaluate its quality as a building material. A good building stone is expected to maintain its sharp edges and keep its surface free from any signs of powder formation. However, if the edges are broken, and powder is present on the surface, it indicates the presence of calcium carbonate. Stones with such a composition will have poor weathering quality. This test is commonly performed on sandstones.
Attrition Test on Building Stone
The purpose of this test is to determine the rate of wear of stones used in road construction, which measures their resistance against the grinding action caused by traffic. The testing procedure involves taking samples of stones and breaking them into pieces about 60mm in size. These pieces, weighing 5 kg, are then placed in both cylinders of the Devil’s attrition test machine, which have a diameter and length of 20 cm and 34 cm, respectively. The cylinders are closed, and their axes are set at a 30-degree angle with the horizontal. The cylinders are then rotated about the horizontal axis at a rate of 30 rpm for a period of 5 hours. After this time, the contents are removed from the cylinders and passed through a sieve with a mesh size of 1.5mm. The weight of the material that remains on the sieve is measured, and the percentage wear is calculated using the formula: Percentage wear = (Loss in Weight/Initial Weight) x 100.
Crushing Test on Building Stone
The given scenario describes a testing procedure for stone cubes, which involves cutting them into a standard size of 40 x 40 x 40 mm and finishing them to a fine quality. Only a maximum of three cubes can be tested at a time, and they must be placed in water for approximately 72 hours before the test to ensure saturation.
During the test, a load is applied axially on the cube using a crushing test machine. The load-bearing surface is covered with a 5mm thick layer of plaster of paris and plywood. The rate of loading is set at 140 kg/sq.cm per minute.
The crushing strength of the stone per unit area is determined by dividing the maximum load at which the sample crushes or fails by the area of the bearing face of the specimen. This test is used to evaluate the strength and durability of the stone and is important for construction and engineering projects that require the use of natural stone.
Crystalline Test on Building Stone
The experiment involves taking at least four cubes of stone with a side length of 40mm. The cubes are first dried for a period of 72 hours and then weighed to determine their initial weight. After this, the cubes are immersed in a 14% solution of Na2SO4 for 2 hours. They are then dried at a temperature of 100 degrees Celsius and weighed again to determine the weight difference.
This process of drying, weighing, immersion in Na2SO4 solution, and reweighing is repeated at least five times. Each time, the change in weight is recorded and expressed as a percentage of the original weight. The purpose of this experiment is to observe the effect of repeated immersion in the Na2SO4 solution on the weight of the stone cubes.
The decay of stone due to weathering is often caused by the crystallization of CaSO4 in the pores of the stone. However, CaSO4 has low solubility in water and is not used in this experiment.
Freezing and thawing test
The experiment involves subjecting a stone specimen to various conditions and observing its behavior. Firstly, the stone is immersed in water for a duration of 24 hours. Subsequently, it is placed in a freezing machine set at -12 degC for another 24 hours. To prevent any interference from external factors such as wind, sun rays or rain, the thawing or warming process is conducted in the shade, at atmospheric temperature. This sequence is repeated multiple times and the response of the stone is carefully monitored throughout the experiment.
Hardness Test on Building Stone
To determine the hardness of a stone, a test is carried out using Dorry’s testing machine. A cylindrical sample is taken from the stone, with a diameter and height of 25mm each, and it is weighed. The sample is then placed in the testing machine and subjected to a pressure of 1250 gm.
Next, an annular steel disc is rotated at a speed of 28 rpm, and coarse sand of standard specification is sprinkled on top of the disc. This process is continued for 1000 revolutions. After this, the specimen is taken out and weighed again.
The coefficient of hardness is then calculated using the following equation: Coefficient of hardness = 20 – (Loss of weight in gm/3). The loss of weight is determined by subtracting the weight of the sample after the test from its initial weight. The result is divided by three, and the quotient is subtracted from 20 to obtain the coefficient of hardness.
Impact Test
To determine the toughness of a stone, an impact test is conducted using a Page Impact Test Machine. The first step involves taking a cylindrical sample of the stone with a diameter and height of 25mm each. The sample is then placed on the cast iron anvil of the machine. A steel hammer, weighing 2 kg, is allowed to fall vertically in an axial direction onto the specimen.
The impact test is conducted by gradually increasing the height of the hammer’s fall. The first blow has a height of 1 cm, and the second blow has a height of 2 cm. This pattern is continued, with the height of each subsequent blow being increased by 1 cm. The number of blows required to break the specimen is noted. If the specimen breaks at the nth blow, then the value of ‘n’ represents the toughness index of the stone.
Microscopic Test
To examine the properties of a sample test, it is necessary to subject it to microscopic examination. This involves taking sections of stones and placing them under a microscope to study various aspects of their composition. One such property that is commonly studied is the average grain size of the stone. Additionally, the existence of pores, fissures, veins, and shakes can also be observed under the microscope.
Another aspect that is studied is the mineral constituents of the stone. This can be crucial in determining the quality of the stone and its suitability for a particular purpose. The nature of the cementing material in the stone is also analyzed to ascertain its strength and durability. It is important to identify the presence of any harmful substances that may be present in the stone and pose a threat to human health.
Finally, the texture of the stone is also studied to determine its appearance and how it may behave in different environments. All these properties can be observed and analyzed through microscopic examination, which is an essential process in determining the quality and suitability of a stone for various applications.
Smith’s Test
A test is conducted to determine if there is any soluble matter present in a sample of stone. This test involves taking a few chips or pieces of the stone and placing them inside a glass tube. Clear water is then poured into the tube, and the tube is left undisturbed for approximately an hour.
After the hour has elapsed, the tube is vigorously stirred or shaken. If the stone contains any earthy matter that is soluble, the water inside the tube will become dirty. On the other hand, if the stone is durable and free from soluble matter, the water will remain clear even after being shaken.
This test is important as the presence of soluble matter in the stone can lead to issues such as discoloration or even structural instability. By performing this simple test, one can quickly determine if the stone is suitable for a particular application.
Water Absorption Test
The test for determining the properties of a stone sample involves several steps. First, a cube weighing approximately 50gm is prepared from the sample and its actual weight, denoted as W1 gm, is recorded. The cube is then placed in distilled water for 24 hours and removed, with surface water wiped off using a damp cloth. The cube’s weight is measured again and recorded as W2 gm.
Next, the cube is suspended freely in water, and its weight is measured and recorded as W3 gm. The volume of displaced water can be calculated as W2 – W3. The percentage absorption by weight after 24 hours is obtained by using the formula (W2 – W1) x 100 / W1, while the percentage absorption by volume after 24 hours is calculated using (W2 – W1) x 100 / (W2 – W3).
The cube is then boiled in water for 5 hours before being removed and its weight recorded as W4 gm, with surface water wiped off using a damp cloth. The percentage porosity by volume is determined using (W4 – W1) x 100 / (W2 – W3), while the density is calculated as W1 / (W2 – W3) kg/m3. The specific gravity can also be calculated as W1 / (W2 – W3).
Finally, the saturation coefficient, which represents the ratio of water absorption to total porosity, is calculated using (W2 – W1) / (W4 – W1). These values provide information about the properties of the stone sample, such as its porosity, density, and absorption capacity.
FAQs
1. Which test is required to check the strength of stone?
Crystallization test is one of the common tests used to determine the strength and durability of stone. Another commonly used test is the flexural strength test, which measures the ability of the stone to resist bending or breaking under a load. There are also other tests such as the compressive strength test, which measures the stone’s ability to resist compression or crushing, and the abrasion resistance test, which measures the stone’s ability to resist wear and tear due to friction. The specific test used may depend on the type of stone and the intended use.
2. How do you identify a building stone?
To identify a building stone, it is necessary to identify its specific rock type and note its characteristics. The following are some common ways to identify a building stone:
1. Color: The color of the stone can provide important clues to its identity. For example, granite is typically gray, pink or white, while sandstone is often brown or red.
2. Composition: The composition of the stone can also provide important information. For example, limestone is composed primarily of calcium carbonate, while granite is composed of feldspar, quartz, and mica.
3. Texture: The texture of the stone can also provide important information. For example, sandstone has a coarse texture, while limestone can have a smooth, fine-grained texture.
4. Sedimentary structures: If the stone is a sedimentary rock, it may contain sedimentary structures such as bedding planes or ripple marks, which can help identify its origin.
5. Fossils: If the stone contains fossils, they can be used to identify the type of organism that lived in the area where the stone was formed.
6. Weathering appearance: The appearance of the stone after exposure to the elements can also provide important information. For example, some types of sandstone will weather to form distinctive features such as honeycomb patterns or pitting.
By examining these characteristics, it is possible to identify the specific rock type and determine the source of the building stone.