LIME IN CONSTRUCTION INDUSTRY: ALL YOU NEED TO KNOW

LIME IN THE CONSTRUCTION INDUSTRY

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 set by carbonation. Pozzolans such as volcanic ash or ground clay bricks and tiles were often added to give a higher strength.

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 712-1984 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.

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 the addition of pozzolanic 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 the laboratory as per Indian Standard code, IS 6932-1973 to check the 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 these classifications is explained below.

Various methods for Laboratory Testing on Building Lime as per Indian Standard Codes

There are different tests that are conducted under routine on building limes, following are the details of some tests :

1. Determination of Residue on the Slaking of Lime

This test is provided in IS 6932 (Part 3).

• Firstly, the sample for testing is sieved through 2.36mm IS sieve.
• The residue (if any) 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.
• This should be kept in mind that 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 5 kg is slaked, by adding them in smaller quantities with the water in the required quantity.
• This must be maintained at 50 and 100 ± 2 degrees Celsius for 5 minutes. The mix is stirred continuously at this temperature maintained, and allows standing 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 degrees 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.

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 24 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 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

This is conducted in the Le Chatelier apparatus that would help in determining the quality of the lime. The quality in the sense will help in knowing the unsoundness or the disintegration property of the material. There are chances of the presence of over burnt material called the cores, that if used in plastering, they remain hydrated and with time they pop out. This phenomenon is undesirable and is called as popping. So, to reduce this effect the material used for the same must be completely slaked that is free from overburnt material.

The test is carried out following the mix ratio 1:3:12 as cement to hydrated lime to standard. The mixture taken is gauged and mixed with water. The quantity of water taken is 12 percent by mass of the weight of the dry mixture. Three test molds are greased and filled with the above-prepared mix. The mold is placed over a standard dry plate. The three molds are now covered with a non-porous plate.

A small weight is placed on the three of the molds and kept undisturbed for a period of 1 hour. The distance between the indicator is measured. It keeps it in damp air and then in steam at atmospheric pressure for 48 and 3 hours respectively. Then allowed to cool and the distance between the pointers are measured. To consider the expansion of cement, a reduction of 1 mm is made of the obtained values. The effectiveness of lime slaking and its quality is checked through this method.

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.

Compressive strength:

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

• The free calcium amount is 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.
• The age of lime mortar is between 20-30 years Mortar is generally very durable and has a typical lifespan of between 20-30 years, after which repairs (or repointing) can be necessary to fill cracks or gaps that may begin to appear. Mortar may be provided in its component parts and mixed on-site, or factory-mixed.

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 damage to 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.

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. Should have Cementing capability– This is obtained by their carbonation with carbon dioxide. Lime is used as lime mortar for brick masonry construction.
2. Should have ahigher acid resistance– due to its alkaline nature
3. Should 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).

 

Building Lime Physical Requirements

As per IS 6932-1973 (Part 1 to 11)

Following are the applications of building lime in the construction

1. In masonry construction-For the construction of the monument, retaining walls. Also, used in load-bearing
2. In structural applications like canopies, arches, domes of different sizes and forms.
3. It is used for the construction of wall structures like wells, fountains, and water channels.
4. It is used for plastering purposes– For different types like decorative, plain plastering.
5. It is used to make intricate patterns as well as geometrical profiles.
6. It is used for finishing works.

Different Types of Field Tests on Building Lime

Different types of field tests on building lime to check the quality of lime to be used in mortar mix for construction works and their procedures are discussed. Tests on building lime can be carried out as field tests or as laboratory tests. The detailed laboratory tests on building lime as per IS 6932 – 1973 is discussed in another article. Simple field tests on building lime helps to define the quality of lime when it is directly bought from the kiln. Mainly the field tests are used to test the quality lime in the form of quicklime i.e. calcium oxide (CaO). The industrial consumers demand minimum lime content. If 60 % of calcium oxide for hydrated lime is the minimum requirement means that nearly 80% is the maximum that is possible. In situations where lime is used for chemical stabilization, in road making, it is the impurities in chemical means, in the form of lime that is important.

Samples for Physical Tests on Building Lime

The test samples that is required to conduct the physical test must be collected as fast as possible before it starts to deteriorate. To carry out the test for quicklime and for hydraulic lime, from each lot, 3 samples were taken. The sample size that is recommended for quicklime is given below. For tests on hydraulic lime, the weight should not be lesser than 5kg.

The Sample Size for Physical Test for Building Lime

Lot Size, (Tonne)	Gross Sample Size for Lump Quicklime,( Kg)	Gross Sample Size for Powdered Quicklime, (Kg)
Up to 100	500	250
101 to 300	1000	500
301 to 500	1500	750
501 to 1000	2000	1000

The structures constructed with lime‐based mortars have the more complex long‐term performance of mortars as compared with concrete. Restoration of mortars & durability depends on :

‐ The environmental exposure conditions  (inducing climatic changes, sulfate attack,  salt contamination from air pollution, acid rain, frost,  wetting‐drying,  wind weathering,  biological attack, thermal dilation, etc ).

‐ The characteristics of the substrate to which a mortar is applied (compatibility with substrate).

‐ The ingredients used to make the mortar,  i.e. its composition  (binder,  aggregate,  additives,  admixtures, and water), influence porosity,  mechanical and elasticity characteristics, as well as deformability.

‐ Maintenance (lack of which leads to premature failures, worsening damage).

‐ On-site construction practices.

Furthermore,  historic structures often include different composite masonry elements,  consisting of masonry units and mortars,  such as single‐leaf or two‐leaf stone masonry walls. Lime‐based mortars may serve as bedding, re‐pointing, rendering/plastering mortars, or even complete the missing parts of ancient floors or architectural surfaces.

 

The various issues related to lime the  repair  works carried out with lime‐based mortars are intended  to  remedy can include:  

‐ cracking,

‐ rising damp,

‐ salt  accumulation  resulting  in  scaling,  delamination,  granular disintegration,

‐ loss of mortar cohesion, or bond with the substrate,

‐ freeze-thaw damages,

‐ wind & weathering,

‐ color alteration.

In repair works a  systematic diagnostic investigation is made before designing the recipe for a repair mortar.  However,  what mixture was actually applied,  and details of the execution of the work,  as well as long‐term monitoring data, are not often available.

The properties related to the durability of lime‐based mortars for good & long‐term performance are:

• Porosity and pore size distribution, are associated with capillary water absorption,  drying,  water vapor permeability,  hygroscopicity,  frost resistance, and salt crystallization.
• Mechanical strength, compressive strength, and tensile strength
• Modulus of elasticity, deformability (capacity of the material to accommodate elastic/plastic deformations).
• Shrinkage (early and long-term).
• Adhesion, shear, flexural and tensile bond.
• Thermal dilation coefficient.
• Specific characteristics such as color and color stability for architectural appearance surfaces and renders, abrasion resistance for flooring mortars, are also considered for the durability of repair
• Specific functional classifications of mortar, and the requirement frameworks they are designed to meet, imply that significant properties relevant to durability will be different for different mortars.
• As is well known,  the hardened porosity of a  mixture of inorganic constituents and water is mainly determined by the water/binder  (W/B)  ratio, since the ultimate water content and porosity relationship is linear for a  great range of materials and it is the most influential parameter for the strength development in the hardened state. Differences in W/B lead to differences in porosity (pores involved in capillary transport).

 

Field Tests on Building Lime for Construction Works

The IS 1624-1974 specifies certain field tests on building lime. These are:

1. Visual Examination

The class C lime will have white color under visual examination

2. Hydrochloric Acid Test

The powdered lime (leveled teaspoon of lime) is taken in a test tube (the quantity will be almost 10cc). To this hydrochloric acid is poured, till the efflorescence ceases. It is kept to stand for 24 hours. The bubbling action of the reaction shows the presence of lime. The insoluble residue in the same shows the presence of inert material (Phenomenon named as adulteration). After 24 hours, a thick gel is formed. If the gel has no kind of flowing capability; It is actually a representation of the presence of class A lime. If the gel has a flowing capability, it is Class B lime. If no kind of gel is formed, the presence of Class C lime is fixed.

3. Ball Test

With the addition of water to lime, a ball shape with lime is made. It is placed in a basin of water after storing it for 6 hours. If after placing in water, any kind of disintegration is seen within few minutes, the Class C lime presence is found. If a little expansion is found, with some number of cracks within it, the Class B lime is detected. If no kind of adverse effect on the ball is found, Class A lime is detected.

4. Impurity Test on Building Lime

Lime of known quantity is taken in a beaker and mixed with water. The solution is then let transfer. The obtained residue is allowed to dry under the sun for a time period of 8 hours after which, it is dried. If the residue is less than 10 % in amount, then the lime is good. If it is between 10 to 20 %, the lime can be considered fair. Above 20%, the lime is regarded as poor or impure.

5. Plasticity Test on Building Lime

The lime is made into a thick paste with a sufficient quantity of water. The sample is left overnight. The next day it is laid over a blotting paper, by means of a knife. This way the plasticity of the lime is checked. A good lime is considered plastic in nature.

6. Workability Test on Building Lime

A lime-sand mortar of 1:3 mix is prepared. This mix is then thrown over a brick wall with the help of a trowel. The sticking quality of the mix is determined through this method. If the mix sticks well the workability of the mix is regarded as good.