LIME IN THE CONSTRUCTION INDUSTRY: ALL YOU NEED TO KNOW
Lime mortar is a traditional building material, and is now only normally used for restoration, and repair of old buildings. It was generally made with a mix ratio of about 1:3 (lime:sand), and sets by carbonation. Pozzolans such as volcanic ash or ground clay bricks, and tiles were often added to give a higher strength.
AS PER IS : 712 – 1984 SPECIFICATION FOR BUILDING LIMES
Building limes shall be classified as follows:
Class A – Eminently hydraulic lime used for structural purposes.
Class B – Semi-hydraulic lime used for masonry mortars, lime
concrete and plaster undercoat.
Class C – Fatlime used for finishing coat in plastering, whitewashing, composite mortars, etc, and with addition of pozzolanie materials for masonry mortar.
Class D – Magnesium/dolomitic lime used for finishing coat in
plastering, white washing, etc.
Class E – Kankarlime used for masonry mortars.
Class F – Siliceous dolomitic lime used for undercoat and finishing
coat of plaster.
Detailed tests on building lime are conducted in laboratory as per Indian Standard code, IS 6932-1973 to check quality and composition of lime suitable as a building material. These tests on building lime is generally are divided into two main classifications: the routine tests and the special tests. A detailed explanation of different tests that comes under each of this classification is explained below.
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
This test is provided in IS 6932 (Part 3). Initially, the sample for testing is sieved through a 2.36mm IS sieve. The residue if present is broken and again it is sieved. The process is repeated till the whole sample pass through the sieve. The quantity of water that is required for the slaking is equal to four times the mass of the quicklime.
Note: For high calcium lime the amount of water will be equal to eight times the mass of the sample. Two samples must be prepared, of quicklime, with a weight of-of, 5 kg is slaked, by adding them in smaller quantities with the water in required quantity. This must be maintained at 50 and 100 ± 2 degrees celsius for 5 minutes. The mix is continuously stirred continuously at this temperature maintained, and allowed to stand for 24 hours. In this standing period, only twice the stirring is carried out. The last stirring is carried out one hour before the commencement of the standard 24 hours. The supernatant liquid is allowed to pass through an 850 micron IS sieve then through a 300 micron IS sieve. The remaining is again stirred and again passed through the same sieve. The residue that is obtained is washed and dried at a temperature of 100±10 degree Celsius to a constant mass. The residues are obtained for two samples that are weighted separately and designated as the percent of the mass of the quicklime test sample.
2. Fineness Test on Building Lime
This test is carried out based on IS: 6932 (Part 4). A 100 g of hydrated lime is undergone a sieve test. The arrangement consists of sieves arranged in such a way that the coarser sieves are placed at the top in a decreasing manner. With the help of a moderate jet of water, the hydrated lime is washed through the sieve from the top, in not more than 30 minutes. The Residue on each of the sieves is dried at a temperature of 100±10 degrees Celsius to a constant mass and is weighed. The obtained is the percentage mass of the hydrated lime sample.
3. Workability Tests on Building Lime
Workability tests on building lime is carried out in the standard flow table that is shown in the figure below.
Fig.1: Standard Flow Table Apparatus for Workability of Building Lime
To test the hydrated lime, at a temperature of 27 ± 2 oC 500g of hydrated lime is mixed with an equal mass of water. This mixture is allowed to stand for 224 hours. The material is allowed twice to pass through the mixer, to make a form of plastic putty. The lower part of the lime putty is spread to a thickness of 110 mm when it is subjected to a bump in the standard flow table. No deviation of more than 1 mm is expected. More water is added if it is stiff. If water is more, it is allowed to withdraw, by placing over a dry absorbing surface. This is how the lime putty sample will acquire the standard consistency. This sample is filled inside the molds. The temperature maintained is 27 ± 2 oC. Care is taken not to fill the molds with air bubbles. The top of the cone is cleaned and leveled. The cone with the material is placed in the center of the table, and the mold is removed At a rate of one turn per second, the handle of the table is turned. The spread of material is the average of three diameters that are measured with a 60-degree gap. This is actually the average diameter that is obtained.
4. Soundness Tests on Building Lime
5. Setting Time Tests on Building Lime
This test is as per IS:6932 PART 11. The Vicat’s apparatus is used and tested similarly to the test conducted for Portland cement.
6. Strength Tests on Building Lime
This test is carried out as per IS:6932- Part 7.
Sample: 12 numbers of 50mm cube Mix: Standard lime to sand mortar in 1:3 mix Temperature Conditions: 72 hours in humidity (90%) then placed in air for 4 days 6 out of 12 cured in water for 7 days. The 14-day compressive strength is determined after at a gradual load of 150N per minute till the specimen crushes. The remaining 6 samples cured for 21 days and 28-day compressive strength is determined. The average strength of samples at 14 and 28 days are obtained.
Transverse Strength Test:
Sample: 25 x 25 x 100 mm mortar specimens Mix: standard lime to sand at 1:3 ratio Cured for 28 days with the mold with the help of a contained at 90 % relative humidity and a temperature of 27± 2oC. At the end of the 28 days, the mold is removed and the specimen is cured in water for 30 minutes. The specimen is tested on a transverse testing machine, placing over 2 rollers placed at a space of 80mm. The concentrated load is applied at the center uniformly at a rate of 150± 15N per minute till the specimen breaks. The modulus of rupture or the transverse strength at 28 days is given by
W = Breaking Load L is the spacing between the rollers. The breadth and the depth of the specimen are b and h respectively.
Factors affecting Properties of Lime Mortar
1. The free calcium amount present in the lime mortar 2. The free lime content and porosity are directly proportional 3. The fat lime or nonhydraulic lime does not set underwater, it sets with time 4. The hydraulic lime sets after the addition of water. This rate depends on the type as well as the characteristic composition of hydraulic lime.
Advantages of Lime in Construction
- Provides building breathing property– the lime was regarded as a material by the society for protection against the depletion of ancient buildings. This material let the building to be vapor permeable, thus allowing to breathe. This reduces the chances of trapped moisture and the damage of the building.
- Renders Comfortable Environment– Absorbing moisture by the lime, stabilize internal humidity
- Ecological Benefits– energy conservation than cement, small scale production of lime is possible
- Protection of adjacent materials– Porous texture of lime handle the moisture movement, without affecting the adjacent materials
- Provides good workability
- Durability is high
- Beautiful finish for the building
- Self-healing properties– Any movement of the building made of lime, creates micro-cracks. The presence of moisture makes the free lime active to precipitate and heal these micro-cracks
The cementing Action of Lime
The calcium hydroxide reacts with the carbon dioxide in the atmosphere to give calcium carbonate that gains cementing properties. This reaction is called as carbonation. Hence the cementing action of lime is dependent on the rate of carbonation. For economical consideration, sand is incorporated into the lime mixture. This not only provides bulkiness to the mixture but also helps to make the mortar porous in nature. This hence would help in letting the carbon dioxide freely circulate within them, to promote carbonation. Another variation for this is by the addition of Pozzolana into lime. These are minerals with high reactive silica. These react with lime in the presence of water and the cementing compounds are formed. These, therefore, do not require any air to promote the reaction. Hence hydraulic lime is those that have reactive silica (Pozzolana) within in it, or added ones, that cans set underwater.