To determine the compressive strength of mortar cubes.

To determine the compressive strength of mortar cubes.

CODE

The compressive strength of mortar is determined by using 2-inch or 50-mm cubes as per ASTM C109/C109M—Standard Test Method for Compressive Strength of Hydraulic Cement Mortars.

THEORY

Mortar is a combination of cement and sand mixed with water. It is used for masonry works such as brick masonry and stone masonry and for plastering walls, columns, etc.

Common mix ratios of mortar used in masonry works are 1:3, 1:4, and 1:6 of cement to sand ratio. For important masonry structures such as brick walls, a 1:3 ratio is used.

Why the Compressive Strength Test of Mortar is Important?

Generally, masonry structures are constructed as load-bearing. For example, load-bearing walls, load-bearing masonry columns, etc. are constructed for residential and other masonry buildings. For masonry buildings, foundations are also constructed with brick masonry.

For load-bearing masonry construction, it is important to know the compressive strength requirement of masonry to withstand the load subjected to it. A masonry wall is subjected to compressive loads from floors above it and should have sufficient strength to withstand it. So, masonry compressive strength should be enough to support the loads on the wall.

Apparatus

• 7.06 cm cubes moulds (50 cm²face area),
• apparatus for gauging and mixing mortar,
• vibrator,
• compression testing machine, etc

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Procedure for Compressive Strength of Mortar

• Take 200 g of cement and 600 g of standard sand in the mix ratio (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 the spherical form; elongated and flattened grains are present only in very small quantities.
• Standard sand shall pass through a 2 mm IS sieve and shall be retained on a 90-micron IS sieve with the following particle size distribution.
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• Mix the cement and sand in dry condition with a trowel for 1 minute and then add water. The quantity of water shall be (p/4 + 3)% of the combined weight of cement and sand, where p is the percentage of water required to produce a paste of standard consistency determined earlier.
• Add water and mix it until the mixture is of uniform color. The time of mixing shall not be < 3 minutes & not > 4 minutes.
• Immediately after mixing the mortar, place the mortar in the cube mold and prod with the help of the rod. The mortar shall be prodded 20 times in about 8 seconds to ensure the elimination of entrained air.
• If a vibrator is used, the period of vibration shall be 2 minutes at the specified speed of 12000±400 vibrations/minute. Then place the cube molds at a temperature of 27±2 ^oC and 90% relative humidity for 24 hours.
• After 24 hours, remove the cubes from the mold and immediately submerge in clean water till testing. Take out the cubes from the 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. A test should be conducted for 3 cubes and report the average value as the test result for both 7-day and 28-day compressive strength.

Result of Mortar Cube Test

Compressive strength at 7 days =……….N/mm2

Compressive strength at 28 days =……….N/mm2

Calculations of Compressive Strength of Mortar

Range Calculation

Allowable compressive stress =

Area of cross-section of cubes = 50 cm2

Expected load = stress x area x f.s.

The range to be selected is…

Compressive Strength of Mortar

Breaking load =…

Area of cross section=……………….

Compressive strength=……………………