Various laboratory tests are conducted on building lime for its suitability as material for construction works. Test for consistency of putty is discussed.
Laboratory Testing of Lime to be Used as a Building Material in Construction
Following are the various laboratory tests conducted to lime to find its suitability as a building material:
- Loss on ignition test (LOI) on lime
- Reactivity assessment of quick lime
- Rapid sugar test of lime
- Volume yield test of quicklime
- Consistency test of putty
The special tests that are a category of laboratory tests conducted on building lime are described below:
1. Loss on Ignition Test (LOI) on Building Lime
The relative degree of calcination that is happened in the lime can be monitored with the help of the loss of ignition test.
The process involves heating a given sample of lime to a higher temperature. This is ensured to make all the possible volatile substances present in the lime sample to escape. This escape can bring a change of mass of the sample when compared to the initial mass.
The detailed loss of ignition of lime can be explained by the following steps in sequence:
I. The given quantity of sample is placed in Tare
II. For a time already set, the tare is placed in a temperature controlled furnace
III. The sample is allowed to cool in an atmosphere that is water free and carbon dioxide free
IV. The mass of the final quantity is determined
V. To ensure the completion of mass change, the whole steps can be repeated.
2. The Reactivity Assessment of Quick Lime
When water is added to quicklime, the hydration of lime will happen. This will result in the evolution of heat, as the process is highly exothermic in nature.
Quicklime that is lightly burned has higher chances of fast rate hydration, when compared with the quicklime that is hard, due to over burning. This phenomenon and concept are used to determine the degree of burning of the quick lime as well as to monitor the reactivity of the quicklime.
3. Rapid Sugar Test on Lime
Rapid sugar test is used to determine the available lime.
The method is carried out by taking a sample of sieved hydrated lime in 500mg on to a flask that consists of 20ml of distilled water. The flask is heated for two minutes, after swirling the corked flask.
To this mixture, 150 ml water and 15g of granulated sugar is added. After the mentioned additions, the flask is recorked and at an interval of five minutes, the flask is shaken. Later the flask with the solution is allowed to stand undisturbed for a period of one hour.
The next procedure involved is titration. The solution in the flask is titrated against a solution of standard hydrochloric acid (HCl) with two drops of phenolphthalein. The titration is carried out based on the standard procedure. The final reading is noted. The conversion is based on the principle that, 1ml of acid solution will represent an equivalent amount of available lime (CaO) in 1%.
4. Volume Yield of Quicklime
Volume yield of quicklime test is based on Indian standard codes IS 6932-Part 6. There is a chemical reaction happening when quicklime is mixed with water, whose amount is three to four times the mass of quicklime.
The entire mixture undergoes a process of boiling. This is due to the reaction of calcium oxide (CaO) reaction with the water which gives the product calcium hydroxide. This reaction will result in liberation of heat in large amount.
The final product that is formed is a suspension of the finely divided calcium hydroxide in water. This can be accompanied by magnesium hydroxide or oxide if the testing sample is dolomite lime. Now, this product is slaked lime, that is cooled and screened to make it suitable for the construction process.
When the mass is cooled, the semi-fluid mass undergoes stiffening to a required mode. The consistency of putty is achieved that would facilitate its working using a shovel and desirable modes.
The type of the putty used, the degree of burning of lime (lightly or over burnt), and the slaking conditions will affect the yield of putty for the construction process. It mainly accounts for an amount of 70 to 100 ft3 of putty, from one ton of the quicklime material.
The major use of putty is in the application of masonry mortar. This is because of the plasticity and workability advantageous the putty provides to the mortar mix, that would quality in the construction of masonry.
Consistency of Putty
The southard viscometer is a measuring instrument that is used to adjust the consistency of the putty. The instrument possesses a metal cylinder with an internal diameter of 50mm, that is mounted on a wooden platform.
Without the turning or movement of the cylinder, a close-fitting piston will move up and down. The working stroke of the device is 65mm. To measure the degree of slumping, due to the ejection of the putty, a metal bridge is attached. The measuring instrument is provided with a putty density vessel when it is supplied.
Sufficient putty is added to a filter cloth, which is then fold in the form of a bag. The putty is allowed to drain. This is done by suspending the bag by a chord, which is above the vessel. When moderate pressure is applied to the bag, draining process can be accelerated.
13mm is the desired slump. Hence the consistency must be adjusted to get this slump. By knowing the known volume of the putty and with the help of a density vessel, the density of the putty is found with the following formula
Volume of quicklime (ml) = 0.70/(d-1)
Where ‘d’ is the density of the lime putty.
Standard Equipment for Laboratory Tests on Building Lime
The most commonly used standard equipment for laboratory tests on building lime are:
1. Building Lime Mortar Mixer
A motor mixer is an electrically driven device. It is an epicyclical type, having stainless steel mixing bowl. It consists of a nominal capacity of 5 liters. The shape and dimension of the same are shown in figure-1 and figure-2.
The mixing bowl is provided with sufficient means to properly connect to the mixing stand so that the bowl is securely fixed during the mixing process. The mixing blade is such a way that it rotates within the bowl in planetary motion. This movement is facilitated by the motor.
The initial slow speed of the blade is at the rate of 140± 5rpm. Later a planetary motion, with a speed rate of 64 ± 5 rpm. The second speed after this is at a rate of 285 ± 10 rpm, which have a planetary motion of 125rpm. The electric motor assembled for this have a power of 150 W.
The mixing initially starts at a slower speed. The mixer allows adjusting during the mixing process also. This is to keep a minimum clearance of 2.5mm between the blade and the lower inner end of the mixing bowl. This clearance must not be less that diameter of the sand used for the mix.
Fig.1: Building Lime Mortar Mixer Bowl
Fig.2: Lime Mortar Mixer Blade
2. Standard Flow Table for Tests on Building Lime
The workability or the consistency of the mortars, as well as building lime, is determined with the help of the flow table as shown in figure.3. the flow table is available in two forms, manual operated and motor operated. With the help of a motor speed reducer, motor operated flow table arrangement will work.
The system has drops that are already preset, that it will end up automatically at the end of each cycle. The whole arrangement will include the flow mold as well as the tamping rods. Certain arrangement will also have the filling hopper along with the remaining.
Fig.3: Diagram showing a standard flow table and a truncated conical flow mold