COMPRESSIVE STRENGTH OF MORTAR CUBES
To find the compressive strength of standard cement sand mortar cubes.
7.06cm cubes moulds (50cm2 face area), apparatus for gauging and mixing mortar, vibrator, compression testing maching etc.
Take 200gm of cement and 600gm of standard sand in the proportion 1:3 by weight) in a pan. (The standard sand shall be of quartz, of light, gray or whitish variety and shall be free from silt. The sand grains shall be angular, the shape of grains approximating to the spherical form, elongated and flattened grains being present only in very small quantities.
Standard sand shall pass through 2mm IS sieve and shall be retained on 90 microns IS sieve with the following particle size distribution.
Mix the cement and sand in dry condition with a trowel for 1minitues and then add water. The quantity of water shall be (p/4+3)% of combined weight of cement and sand where, p is the % of water required to produce a paste of standard consistency determined earlier. Add water and mix it until the mixture is of uniform colour. The time of mixing shall not be < 3 minutes & not > 4 minutes. Immediately after mixing the mortar, place the mortar in the cube mould and prod with the help of the rod. The mortar shall be prodded 20 times in about 8 sec to ensure elimination of entrained air. If vibrator is used, the period of vibration shall be 2minitues at the specified speed of 12000+-400 vibrations /minutes. Then place the cube moulds in temperature of 27±2o C and 90% relative humidity for 24 hours. After 24 hours remove the cubes from the mould and immediately submerge in clean water till testing. Take out the cubes from water just before testing. Testing should be done on their sides without any packing. The rate of loading should be 350 kg/cm2/minute and uniform. Test should be conducted for 3 cubes and report the average value as the test result for both 7day and 28 day compressive strength.
Compressive strength at 7 days =……….N/mm2
Compressive strength at 28 days =……….N/mm2
Allowable compressive stress=
Area of cross section of cubes=50cm2
Expected load=stress x area x f.s=
Range to be selected is ………..
Breaking load= ……………….
Area of cross section=………………….