Building lime is a crucial material used in construction, known for its binding properties. It has been a staple in building practices for centuries, particularly in masonry work and plastering. However, to ensure the material’s suitability for use in construction, it is essential to test its quality and composition. These tests, as per the Indian Standard code IS 6932-1973, provide guidelines for determining whether the lime meets the required standards for performance and durability. The tests are categorized into routine and special tests, each serving a specific purpose in evaluating the lime’s properties. In this article, we explore these tests and their significance in ensuring that building lime is of the highest quality.
Types of Tests on Building Lime
The testing procedures for building lime can be broadly classified into two categories:
- Routine Tests
- Special Tests
These tests focus on assessing the key characteristics of lime that affect its suitability as a building material. Let’s examine the different tests under each category.
Routine Tests on Building Lime
Routine tests are conducted regularly to evaluate the basic properties of building lime. These tests assess the physical characteristics and behavior of lime in different conditions.
1. Determination of Residue on the Slaking of Lime
The determination of residue on the slaking of lime is a crucial test to assess the quality of lime. This test, outlined in IS 6932 (Part 3), helps to determine how much residue remains after slaking quicklime with water. The process begins by sieving the lime sample through a 2.36mm IS sieve. Any residue is then broken and re-sieved, repeating the process until the sample passes through the sieve.
During the slaking process, a precise amount of water is added to the lime. For high calcium lime, the amount of water is typically eight times the mass of the sample. The test conditions require that the slaked lime be maintained at a temperature of 50-100°C for five minutes and stirred continuously. After a 24-hour period, the residue is dried at 100±10°C and weighed to determine the mass percentage of residue.
This test is significant because it ensures that the lime is free of impurities or over-burnt material that could affect its performance.
2. Fineness Test on Building Lime
The fineness of building lime plays a crucial role in its strength and workability. As per IS 6932 (Part 4), a 100g sample of hydrated lime undergoes a sieve test. The lime is washed through a series of sieves, with coarser sieves placed at the top. Water is used to wash the hydrated lime through the sieves within 30 minutes, and the residue on each sieve is dried at 100±10°C.
The percentage of the residue is then calculated to determine the fineness of the lime. Finer lime particles generally contribute to better strength and workability in construction applications, making this test an essential part of lime assessment.
3. Workability Tests on Building Lime
Workability is a critical property of building lime, particularly when used in plastering and masonry. To assess the workability, hydrated lime is mixed with an equal mass of water at a temperature of 27±2°C. The mixture is allowed to stand for 24 hours, after which it is stirred twice to form a plastic putty. The consistency of the putty is tested by placing it on a standard flow table apparatus.
The material’s spread on the table is measured by calculating the average diameter of the spread at three different points, forming an angle of 60 degrees. The consistency of the mixture can be adjusted by adding or removing water to ensure that it meets the required workability standards.
4. Soundness Tests on Building Lime
Soundness refers to the ability of lime to resist disintegration after it has been slaked. This test is essential for ensuring that lime used in construction will not undergo undesirable expansion or cracking over time. The test is conducted using the Le Chatelier apparatus, which measures the expansion of lime when exposed to steam.
The lime sample is mixed with water in a specified ratio, and the mixture is placed in molds that are subjected to damp air and steam under controlled conditions. The distance between pointers in the apparatus is measured to determine the degree of expansion. Excessive expansion indicates the presence of unsound lime, which can lead to structural problems like cracking and “popping” in plaster.
5. Setting Time Tests on Building Lime
The setting time of lime is a critical factor that affects its usability in construction. The Vicat’s apparatus, commonly used for cement testing, is employed to measure the setting time of building lime as per IS: 6932 (Part 11). The apparatus consists of a needle that is lowered into the lime paste at regular intervals. The time taken for the needle to penetrate to a specific depth indicates the initial and final setting times.
Understanding the setting time is vital because it informs construction workers about when the lime mixture can be worked with and when it will begin to harden. This knowledge ensures that the material is applied efficiently during construction.
Special Tests on Building Lime
While routine tests assess the general properties of lime, special tests provide more in-depth analysis, especially in terms of its strength and durability under load.
1. Strength Tests on Building Lime
Strength tests are essential for determining the load-bearing capacity of lime in construction. These tests typically include compressive and transverse strength evaluations.
- Compressive Strength Test:
The compressive strength test involves preparing 12 cubes (50mm each) of lime mixed with sand in a 1:3 ratio. The samples are cured under controlled conditions (72 hours in 90% humidity, then placed in air for 4 days). After curing for 7, 14, and 28 days, the cubes are subjected to a gradual compressive load until failure. The maximum load sustained by the cubes is used to calculate the compressive strength. - Transverse Strength Test:
This test measures the ability of lime mortar to resist bending or breaking under stress. Mortar specimens (25x25x100 mm) are prepared and cured for 28 days under specified humidity and temperature conditions. After curing, the specimens are placed on rollers, and a transverse load is applied until the specimen fractures. The modulus of rupture, or transverse strength, is then calculated.
Both these tests provide insights into the structural integrity of lime and its suitability for different building applications.
Laboratory tests on building lime, as per the Indian Standard IS 6932-1973, are essential for ensuring the material meets the required specifications for use in construction. These tests, ranging from simple residue determination to complex strength evaluations, provide a comprehensive understanding of lime’s properties. By conducting these tests, builders and engineers can ensure that the lime used in construction projects is of high quality, durable, and capable of withstanding the stresses and strains of everyday use. Adhering to these standards ensures safer, more reliable construction and contributes to the longevity and stability of buildings and infrastructure.