Concrete elasticity, a critical property, is the measure of a material’s response to applied stress and strain. To precisely determine the modulus of elasticity of concrete, a laboratory test known as the compression test is conducted on a cylindrical concrete specimen.
The test involves two main stages: setting up the compressometer and the application of load and testing.
The compressometer, a device vital in the compression test, is set up as follows:
Two frames (top and bottom) are assembled with the help of spacers, ensuring stability.
The pivot rod is positioned on screws, which are then locked in place, keeping the frames loosely tightened.
Once assembled, the compressometer is placed centrally on the concrete specimen on a level surface.
After positioning, the screws are tightened, securing the compressometer on the specimen. The spacers can then be unscrewed and removed.
The actual testing procedure involves the following steps:
The specimen with the compressometer setup is placed on the compression testing machine platform and centered properly.
Load application is performed continuously at a rate of 140 kg/cm²/minute until a stress value of (c+5) kg/cm² is reached.
Once the stress value is attained, it is maintained for 60 seconds and then reduced to a stress of 1.5 kg/cm².
Load is increased until the stress of (c+1.5) kg/cm² is reached, and compressometer readings are recorded. Load is then gradually reduced, and readings are recorded at 1T intervals.
The test is repeated, and compressometer readings are recorded again.
Observations are used to plot the load-deflection graph. Tangents are drawn at the initial portion and the point equal to the working stress. A line is drawn joining both points.
Various modulus values are calculated from the load-deflection graph:
The report includes essential information such as identification mark, test date, specimen age, and nominal dimensions.
In conclusion, the comprehensive test procedure outlined above provides a reliable method for determining the modulus of elasticity of concrete, a fundamental aspect in structural analysis.