Compressive Strength of Concrete Determination
Introduction
Out of many test applied to the concrete, this is the utmost important which gives an idea about all the characteristics of concrete. By this single test one judge that whether Concreting has been done properly or not. For cube test two types of specimens either cubes of 15 cm x 15 cm x 15 cm or 10cm x 10 cm x 10 cm depending upon the size of aggregate are used. Concrete is poured in the mould and tampered properly so as not to have any voids. After 24 hours these moulds are removed and test specimens are put in water for curing. The top surface of these specimens should be made even and smooth. This is done by putting cement paste and spreading smoothly on whole area of specimen. These specimens are tested by compression testing machine after 7 days curing or 28 days curing. Load should be applied gradually at the rate of 140 kg/cm2 per minute till the Specimens fails. Load at the failure divided by area of specimen gives the compressive strength of concrete.
Preparation Of Cube Specimens
Mixing: Mix the concrete either by hand or in a laboratory batch mixer
Sampling:
Curing: The test specimens are stored in moist air for 24hours and after this period the specimens are marked and removed from the molds and kept submerged in clear fresh water until taken out prior to test.
Precautions: The water for curing should be tested every 7days and the temperature of water must be at 25 - 27oC.
Objective(s) of the Experiment
The test is carried out to determine the compressive strength of hardened concrete
Equipments and Materials Needed
The machine used for this test is The Compression testing machine or Crushing Machine. Two types of Compression testing machine are available at the Geotechnics and Structure Centre: Digital Crushing Machine and Analog type. The digital crushing machine requires fewer calculations as both the load applied and the resulting stress will be displayed accurately on its screen. It is more accurate as there cannot be parallax error since it is digital.
Procedures
Results and Calculations
Discussion and Conclusion
Percentage strength of concrete at various ages:
The compressive strength of concrete increases as the number of days which it was cured increases. The table below shows the strength of concrete at different ages in comparison with the strength at 28 days after casting. It shows that a properly designed and cured concrete structure is unlikely to fail until it reaches its designed life-time.
References
Credits: Samuel Alalade. Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria.