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.
– Setting Up Compressometer
The compressometer, a device vital in the compression test, is set up as follows:
1. Frame Assembly : Two frames (top and bottom) are assembled with the help of spacers, ensuring stability.
2. Pivot Rod Placement : The pivot rod is positioned on screws, which are then locked in place, keeping the frames loosely tightened.
3. Positioning Compressometer : Once assembled, the compressometer is placed centrally on the concrete specimen on a level surface.
4. Final Adjustment : 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:
1. Platform Placement : The specimen with the compressometer setup is placed on the compression testing machine platform and centered properly.
2. Continuous Load Application : Load application is performed continuously at a rate of 140 kg/cm²/minute until a stress value of (c+5) kg/cm² is reached.
3. Stress Maintenance : Once the stress value is attained, it is maintained for 60 seconds and then reduced to a stress of 1.5 kg/cm².
4. Data Recording : 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.
5. Repeat Test : 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.
