Compressive Strength is more of the critical properties of concrete to be tested as it is linked with load carrying capacity and durability.
Come let’s see how the cubes for the compressive strength test are cast. This is a simple test consisting of cast cubes of concrete tested on the compression testing machine after the concrete hardens. Most of the desirable properties of the concrete are qualitatively related to its compression strength. Generally specimens are cast in steel /cast iron moulds of 150 X 150 X 150 mm.
The moulds should have rigid connection in with phase essential in order to prevent the leakage of mortar during compaction. The cube is filled with fresh concrete in 3 layers and compacted well using standard tamping rod of 16 mm diameter and 60 cm long. Each layer should be compacted with 35 blows. The tamping rod should enter previous layer while tamping the subsequent layer. After compacting the top layer the surface is made in flash with edge of mould using a trowel.
The mould is covered immediately with damp has cloth and left undisturbed for 24 hours. Site specimen should be stored in a 22 degree celsius to 32 degree celsius. The cubes should be marked with suitable identification number when slightly hardened to facilitate easy identification at different edges. After 24 hours the mould are stiffed off and the cubes are to be stored in water for further curing till it is taken out just prior to testing curing water temperature should be maintained at 24 degree Celsius to 30 degree Celsius. The cured cubes are then tested on a compression testing machine after 3, 7 or 28 days.
Summary : Testing for compressive strength of concrete – cube casting
- It is advisable to test the compressive strength of concrete using concrete cubes
- Cubes should be cast in standard cube moulds in the manner indicated
- it is essential to cover the mould with damp hessian for 24 hours and cure the moulded cubes in water tanks. till the time of testing.