Popping and Pitting Test of Lime
Objective
To determine popping and pitting of lime sample as per IS-6932-part-10
Theory
This test is a measure to study the unsoundness of building limes. Popping, pitting and blowing are due to the presence of coarse unslaked or only partially slaked particles. On final slaking, these cause dislodgement of pieces on the surface of the plaster, usually in the form of a cone.
In this test pats are prepared by mixing 70 g of hydrated lime with 70 ml of water and 10 g of plaster of paris. They are subjected to steam action and examined for disintegration, popping and pitting. Any of these occurrences is an indication of unsoundness of lime.
Test Procedure
Step-1 [Gauging/Mixing of Plaster]
The gauging plaster used for popping and pitting test when gauged with 50 percent of its own mass of distilled water and tested by the vicat needle shall have an initial setting time of not less than 15 minutes. The gauging plaster shall be free from pops and pits. Fresh, fine, white and good quality plasters of paris which shows no pops or pits when tested without lime may be used.
Step-2 [Preparation of Test Pats/Specimens]
Four test specimens shall be separately prepared in the manner described under.
Mix thoroughly 70 g of the hydrated lime under test with 70 ml of clean water at a temperature 27±30C and allow soaking for 2 hours.
At the expiration of 2 hours, the lime putty thus obtained shall be thoroughly mixed and knocked up with a trowel, if necessary, with a small additional amount of clean water, so as to obtain a plastic mass. It shall then be spread out on a non-porous surface. 10 g of approved grade plaster of paris (as prepared in step-1) shall then be added, the plaster being scattered evenly over the putty and the whole shall be mixed with the trowel rapidly and thoroughly for 2 minutes.
A flat pat shall then be formed by pressing the gauged material into a ring mould 100 mm in diameter and 5 mm deep, greased inside and resting on a well greased non-porous plate. One gram of petroleum jelly/pat is suitable for greasing when renewed each time.
The gauged putty shall be pressed in small quantities at a time, with the aid of a broad palette knife or spatula, in such a manner as to avoid air bubbles. It shall then be smoothed off in level with the top edge of the ring with not more than 12 strokes of the knife, any excess material being removed in this process. The total time shall not exceed 5 minutes from the time of adding the plaster of paris to the last stroke of the knife for any one pat.
Step-3 [Drying of Pats]
The four pats thus formed shall be left to set for half an hour. They shall then be transferred on their base-plates with or without their ring mould to a well ventilated drying-oven maintained at a temperature between 35 to 450C to be well dried. A period amounting 16 hours should be ample for this purpose but a minimum of 4 hours suffices in many cases.
The pats may be left in the oven either before drying or between the periods of drying.
Any test pats which show shrinkage cracks before steaming, shall be rejected and replaced by fresh pats.
Step-4 [Placing Pats in Steam Boiler]
The four pats, still on their base-plates, shall be placed horizontally in a suitable steam boiler in which the water is already boiling, and subjected to the action of started steam at atmospheric pressure for a period of 3 hours. The steaming vessel shall be so arranged that condensed water cannot drip back on to the face of the pats.
Report
The pats shall then be examined in a good light for disintegration, popping and pitting.
Precautions
Ring mould and non porous plate should be greased uniformly with petroleum jelly.
Press putty in the ring mould with a broad spatula avoiding the entry of air bubbles.
Reference
IS: 6932-Part-10 – Method of test for determination of popping and pitting of hydrated lime.