The quality and composition of lime used as a building material are assessed through laboratory tests according to the Indian Standard code, IS 6932-1973. These tests are divided into two main categories: routine tests and special tests.
Routine tests are the first category of tests used to evaluate the quality of building lime. These tests include assessing the physical and chemical properties of the lime, such as its color, texture, and consistency. They also examine its ability to absorb water, the presence of impurities, and the amount of active ingredients, such as calcium oxide.
The second category of tests, known as special tests, is more specific in nature and includes examining the lime’s behavior under certain conditions. These tests evaluate the lime’s ability to resist weathering, its durability under extreme conditions, and its ability to adhere to surfaces. The tests also analyze the lime’s compatibility with other building materials, such as mortar, bricks, and stones.
By conducting these tests on building lime, it is possible to determine its suitability as a construction material. The results of these tests can be used to ensure that the lime meets the required quality standards for use in building projects. Ultimately, these tests are essential in helping to ensure the safety, durability, and effectiveness of buildings constructed with lime as a building material.
Laboratory Tests on Building Lime as per Indian Standards
The different test that is conducted under routine tests on building limes are:
1. Determination of Residue on the Slaking of Lime
The following test is described in IS 6932 (Part 3). The initial step involves sieving the sample through a 2.36mm IS sieve. If any residue remains, it is broken up and sieved again. This process is repeated until the entire sample has passed through the sieve. The quantity of water required for slaking is equal to four times the mass of the quicklime. However, for high calcium lime, the amount of water required will be eight times the mass of the sample.
To conduct the test, two samples of quicklime, each weighing 5kg, are slaked by adding them in smaller quantities with the required amount of water. The temperature is maintained at 50 and 100 ± 2 degrees Celsius for 5 minutes, while the mixture is continuously stirred. After this, the mixture is allowed to stand for 24 hours, during which time it is stirred twice. The final stirring is done one hour before the 24-hour period ends.
The supernatant liquid is passed through an 850 micron IS sieve, followed by a 300 micron IS sieve. The residue obtained from this process is then stirred and passed through the same sieve again. The remaining residue is washed and dried at a temperature of 100±10 degree Celsius to a constant mass. The residues obtained from both samples are weighed separately and expressed as a percentage of the mass of the quicklime test sample.
2. Fineness Test on Building Lime
The test being conducted is based on IS: 6932 (Part 4) and involves 100 grams of hydrated lime. The setup consists of a series of sieves arranged in a decreasing order of coarseness from top to bottom. A moderate jet of water is used to wash the hydrated lime through the sieves from the top, with the entire process being completed in under 30 minutes. After the sieving is complete, the residue left on each sieve is dried at a temperature of 100±10 degree Celsius until a constant mass is achieved. The dried residue is then weighed to obtain the percentage mass of the hydrated lime sample.
3. Workability Tests on Building Lime
The workability tests for building lime are conducted using a standard flow table, as depicted in the figure provided. The flow table serves as the standard apparatus for assessing the workability of building lime.
Fig.1: Standard Flow Table Apparatus for Workability of Building Lime
The hydrated lime test begins by mixing 500g of hydrated lime with an equal mass of water at a temperature of 27 ± 2 oC. This mixture is left to stand for 224 hours, and is then passed through the mixer twice to create a plastic putty-like consistency. The lime putty is spread to a thickness of 110 mm on the lower part of the lime putty, and is subjected to a bump in the standard flow table. No deviation of more than 1 mm is expected. If the lime putty is too stiff, more water is added, and if it is too watery, it is allowed to withdraw by placing it over a dry absorbing surface. This process continues until the lime putty sample acquires the standard consistency. The sample is then filled into molds, while taking care to avoid trapping air bubbles. The temperature is maintained at 27 ± 2 oC throughout the process. The top of the cone is cleaned and leveled, and the cone with the material is placed in the center of the table. The mold is then removed, and the handle of the table is turned at a rate of one turn per second. The spread of the material is measured as the average of three diameters that are measured with a 60-degree gap, which gives the average diameter of the spread.
4. Soundness Tests on Building Lime
The quality of lime can be determined using the Le Chatelier apparatus, which helps to assess its unsoundness or disintegration properties. Overburnt material, also known as cores, may be present in the lime, and if used in plastering, can lead to undesirable popping over time. To avoid this, the lime used should be completely slaked and free from overburnt material.
The test for lime quality is conducted using a mix ratio of 1:3:12 for cement, hydrated lime, and standard material. The mixture is gauged and mixed with water in a specific proportion. The molds used for testing are greased, and three of them are filled with the prepared mix. The molds are then placed over a standard dry plate and covered with a non-porous plate. A small weight is placed on each mold, and the setup is left undisturbed for an hour.
Afterward, the distance between the indicator is measured, and the molds are kept in damp air and then in steam at atmospheric pressure for 48 and 3 hours, respectively. They are allowed to cool down, and the distance between the pointers is measured again, with a reduction of 1 mm made to account for the expansion of cement.
This method effectively checks the quality and slaking of lime and ensures that the material used is free from overburnt material, preventing popping issues in plastering applications.
5. Setting Time Tests on Building Lime
The test being conducted follows the guidelines set forth in the IS:6932 PART 11 standard. In this particular test, the Vicat’s apparatus is utilized and the testing procedure is conducted in a similar manner to that used for Portland cement. The purpose of the test is to evaluate the behavior of the sample material under specific conditions and to determine its Vicat softening point. By adhering to the standard testing procedures and utilizing the appropriate equipment, accurate and reliable results can be obtained.
6. Strength Tests on Building Lime
This test is carried out as per IS:6932- Part 7.
Compressive strength:
The experiment involved 12 50mm cube specimens made with standard lime to sand mortar mixed in a 1:3 ratio. The specimens were subjected to temperature conditions of 72 hours in humidity at 90% followed by placement in air for 4 days. Six of the twelve specimens were cured in water for 7 days, while the remaining six were cured for 21 days. The compressive strength of the specimens was determined at 14 days and 28 days by subjecting them to a gradual load of 150N per minute until they crushed. The average strength of the specimens at 14 and 28 days was calculated.
Transverse Strength Test:
The mortar specimens, measuring 25 x 25 x 100 mm, were prepared using a standard mix of lime to sand at a ratio of 1:3. They were then cured for 28 days in molds under controlled conditions of 90% relative humidity and a temperature of 27±2oC. After the curing period, the molds were removed and the specimens were cured in water for 30 minutes. The transverse testing was carried out using a testing machine with two rollers spaced 80mm apart. A concentrated load was applied uniformly at the center of the specimen at a rate of 150±15N per minute until the specimen broke. The modulus of rupture or transverse strength at 28 days was determined from the test results.
The relationship between the breaking load (W) and the spacing between rollers (L) can be expressed using the equation W = f(L). Additionally, the dimensions of the specimen, such as its breadth (b) and depth (h), are important parameters to consider. The breadth of the specimen is denoted by the variable b, while the depth is denoted by h. The relationship between these dimensions and the breaking load can also be included in the equation as W = f(b, h). By incorporating these variables, the equation can provide insights into how the breaking load of the specimen may vary based on the spacing between rollers as well as its breadth and depth.