Objective

For determination compressive strength of building lime. 

Reference Standards

IS: 6932(Part VII)-Method of tests for Building Limes (Determination of compressive and transverse strengths).

Equipment & Apparatus

• Oven (300⁰C)
• Compression testing machine 

Test Sample Preparation

1. 500 gm of lime is mixed with 60 to 65 % of water for 5 minutes and then the resulting putty is passed twice through a mixer.
2. 350 g of above putty is mixed with standard sand (mass equal to 3 times the mass of the dry lime i.e. 636 g to 656 g). The lime putty and sand is thoroughly mixed for 10 minutes continuously.

 Procedure

1. Twelve cubes with side 5 cm is prepared from standard lime-sand mortar using metallic moulds.
2. The moulds is filled by hand, the mortar being pressed in with the thumb, lightly tamped, smoothed off with 2 or 3 strokes of the trowel. These cubes are then stored undisturbed in a container for a period of 72 hours in an atmosphere of at least 90 percent relative humidity and at a temperature of 27±2⁰C.
3. After 72 hours the specimens is taken out of the moulds and placed in the air in laboratory for 4 days.
4. When 7 days old the specimen is immersed in clean water and left there until just prior to testing for its strength in the testing machine.
5. After 7 days of storage in water 6 of the cubes is taken out of water, wiped surface-dry and tested for compressive strength in a compression testing machine. This gives strength at 14 days.The load is increased at a rate of 15kg/min.
6. The remaining 6 test specimens is taken out after 21 days and similarly tested the determining the compressive strength at 28 days. 

Calculation

The measured compressive strength of the cubes are to be calculated by dividing the maximum load applied to the cubes during the test by cross-sectional area, calculated from the mean dimensions of the section. 

Reports

The average strength of the 6 specimens is taken as the compressive strength of mortar and the result is expressed kg/cm². 

Safety & Precautions

• Use hand gloves while removing containers from oven after switching off the oven.
• To wear safety shoes & apron during the time of test.
• Before testing, machine should be checked.
• After test electric supply should be off.
• Equipment should be cleaned thoroughly before testing & after testing.
• Petroleum jelly should be applied to the mould.