Building Lime – Properties of Lime, Advantages and Uses in Construction

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Lime is one of the basic building material used mainly as lime mortar in construction. Properties of building lime, advantages, and uses in construction is discussed. The broad category of lime is non-hydraulic and hydraulic lime. The non-hydraulic lime is called as quick lime, fat lime or white lime or as lump lime. Hydraulic lime sets under water and non-hydraulic lime do not set under water. Quick Lime is a form of lime is manufactured by the burning of stone that has calcium carbonate within it. The burning temperature varies, say 900 degree Celsius and above for several hours. This process is called as calcination. The solid product that remain after the removal of carbon dioxide in the calcium carbonate is called as the quicklime.

CaCO₃ (Calcium carbonate) --> CaO (Calcium Oxide – Quick Lime) + CO₂

The quick lime is used as hydrated lime (quick lime with water). This is because it is unstable and hazardous in nature. There is heat liberated when a small quantity of water is added to the quicklime. After this hydration product, a fine dry white powder is obtained, which is called as calcium hydroxide or slake lime. Now this process is defined as the slaking of lime. The slaking of lime is a process that varies depending upon the extent and type of use. For example, the use of lime in plasters or in mortars, make use of lime in dry or putty form. Putty is formed by the addition of a large quantity of water (two to three times its weight). This process promotes a chemical reaction that makes the whole system to boil. A semi-fluid mass is obtained as a stiffened mass on cooling, which is called as the putty. This material after proper screening is used as the material for construction. Hydraulic lime is a factor based product. These have natural pozzolana or added Pozzolana in it that sets under water. The raw material for hydraulic lime is limestone which is impure, that contains calcium carbonate and impurities of clay. These are also calcinated at 900 to 1000 degree Celsius. The reaction is as follows Calcium carbonate + clay impurities (Al2O3 + Si2O3) --> CaO (calcium oxide) + carbon dioxide + Monocalcium silicate(CA), Monocalcium aluminates dicalcium silicate(C2S), dicalcium alumino-ferrite (C2AF)

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 under water, 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

1. 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.
2. Renders Comfortable Environment- Absorbing moisture by the lime, stabilize internal humidity
3. Ecological Benefits- energy conservation than cement, small scale production of lime is possible
4. Protection of adjacent materials- Porous texture of lime handle the moisture movement, without affecting the adjacent materials
5. Provides good workability
6. Durability is high
7. Beautiful finish for the building
8. Self-healing properties- Any movement of the building made of lime, creates micro-cracks. Presence of moisture make 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 to 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, does 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 under water.

Lime Synergy with Pozzolana

As we know, pozzolana is siliceous material that does not gain any cementitious properties. They react with calcium hydroxide to give compounds that gain cementitious properties, at ambient temperature. For the manufacture of Portland Pozzolana cement (PPC), Pozzolana that conforms to natural standards are used. They are either added to final Portland cement product or at the stage of Portland cement clinker grinding. The fineness and the compressive strength of Portland pozzolana cement manufactured (As per IS: 1727:1967) should not be lesser than 320m²/kg and 4.0MPa respectively. For lime reactivity test of the pozzolana chosen, the test is carried out for the fineness at which the pozzolana is blended.

Properties of Lime for Use in Construction

The white powdered slaked lime has a wide range of applications in construction. The properties of lime are:

1. Cementing capability- This is obtained by their carbonation with carbon dioxide. Lime is used as lime mortar for brick masonry construction.
2. Have a higher acid resistance- due to its alkaline nature
3. Gain Pozzolanic activity- this gives cementitious products
4. Sealing of micro cracks- This is done by the precipitation made by the calcium carbonate when carbon dioxide passes through the lime mortar mix.

The table below shows the physical and chemical properties of lime under various classes as per IS:4031-1968 and IS:6932-1972 Part (3 to 10).

Table 1. As per IS 6932-1973 (Part 1 to 11, RA 2009), Building Lime Physical Requirements

Classification of Building Lime

Fat lime and hydraulic lime are the broad classifications of lime. The process of hardening is the main criteria by which the fat lime differs from the hydraulic lime. The IS 712-1973 have classified the lime into different classes. They are Class A, Class B, Class C, Class D, Class E, and Class F. A lime is considered poor lime if it contains more than 30% of impurities.

Applications of Building Lime in Construction

1. Masonry Construction- For the construction of the monument, retaining walls. Also, used in load bearing walls.
2. Structural Applications like canopies, arches, domes of different size and form
3. Used for construction of wall structures like wells, fountains and water channels
4. Used for plastering purposes- For different types like decorative, plain plastering
5. Used to make intricate patterns as well as geometrical profiles
6. Used for finishing works

Read More: Classification of Lime as a Building Material for use in Construction Laboratory Testing of Lime to be Used as a Building Material in Construction Laboratory Tests on Building Lime as per Indian Standard Code IS 6932-1973 Field Tests on Building Lime for Quality in Construction Works