Lime is a popular binding material in the construction industry due to its versatility in applications such as mortar making, plastering, and whitewashing. It is produced through the calcination of limestone, which occurs naturally. To determine the properties and ingredient proportions of limestone, various tests are performed. This article will provide an explanation of the tests and their procedures.
Tests on Limestone
Limestone or powdered limestone has been subjected to four different tests to determine its properties. The physical test aimed to examine the material’s physical characteristics, while the heat test aimed to evaluate its behavior when subjected to high temperatures. The acid test was conducted to investigate the material’s reaction to acidic substances, and the ball test was performed to determine its hardness and resistance to impact. Overall, these tests aimed to provide a comprehensive understanding of the properties and behavior of the limestone/powdered limestone under different conditions.
1. Physical test
Lime can be characterized by various physical properties, such as its color, smell, and texture. The color of lime can provide clues about its purity and composition. For instance, white-colored lime usually indicates pure limestone, while bluish-grey, brown, or dark-colored lime may suggest the presence of hydraulic limestone.
In addition to color, the texture and smell of lime can also provide insights into its properties. Hydraulic limestone typically has a clay-like texture and produces an earthy smell when exposed. Furthermore, if lime appears glittering or shining, it may contain free salts.
Lastly, the presence of bulges or bumps in lime can indicate the type of lime it is. For example, if lime has bulges or bumps, it may be quick lime. Overall, understanding the physical properties of lime can provide valuable information about its composition and potential uses.
2. Heat Test
The purpose of a heat test is to determine the amount of calcium oxide, commonly known as lime, present in a sample of limestone. To conduct this test, a dry sample of limestone is weighed and then heated for a period of four hours over an open flame. During this process, any carbon dioxide present in the limestone will evaporate, resulting in a reduction in weight.
After the four hours of heating, the sample is again weighed to determine the amount of weight lost during the process. This loss of weight is then recorded and used to determine the amount of calcium oxide content present in the sample of limestone. Overall, the heat test is a useful method for analyzing the chemical composition of limestone and determining the amount of calcium oxide it contains.
3. Acid Test
The acid test is a method to determine the amount of calcium carbonate and type of lime present in limestone. The procedure involves adding a teaspoon of powdered lime to a test tube and then adding 10 ml of dilute hydrochloric acid. After stirring the mixture thoroughly, it is left to rest for 24 hours.
After 24 hours, the mixture is observed. If there is high effervescence and less residue at the bottom of the tube, it indicates a high amount of calcium carbonate, which represents pure limestone. On the other hand, if there is less effervescence and more residue left at the bottom of the test tube, it indicates a lower amount of calcium carbonate, and the limestone is treated as impure or hydraulic limestone.
To classify the lime present in the limestone, another test continuation is performed. The test tube is inverted, and the gel formed above the residue is observed. If the gel formed does not move even when the test tube is inverted, it is designated as class A lime. If the gel formed tends to flow when the test tube is inverted, it is designated as Class B lime. If there is no gel formation, then it is designated as class C lime.
The classification table distinguishes between class A, B, and C limes based on the gel formation.
| Lime Class | Lime Type | Lime Percentage | Uses |
| Class A | Eminently Hydraulic Lime | 60 – 70 | Mortar for foundation works, damp place works, etc. |
| Class B | Semi Hydraulic Lime | 70-75 | Mortar for masonry, flooring, etc. |
| Class C | Non-Hydraulic Lime / Fat lime | 93-95 | Plastering, white washing, etc. |
4. Ball Test
The ball test is a common procedure used to determine the class of lime present in a given sample. The test involves several steps, which include the preparation of balls made from powdered lime and water.
To begin, powdered lime is taken and mixed with water until a stiff consistency is achieved. This mixture is then used to prepare balls that are 40 mm in size. The balls are left undisturbed for six hours to allow them to dry and set.
After the six-hour period, the balls are then immersed in a basin of water. Depending on the behavior of the balls in the water, the class of lime present can be determined. If the balls expand and disintegrate within minutes of being submerged in the water, this indicates the presence of class C lime. On the other hand, if there is little to no expansion and numerous cracks are visible on the balls, this indicates the presence of class B lime.
Overall, the ball test is a simple and effective way to determine the class of lime present in a given sample. By following the prescribed steps, it is possible to obtain accurate results and make informed decisions regarding the use of lime in various applications.
FIg 4: Powdered Limestone