Abstract
One of the most important concrete properties for structural concrete design or redesign is the compressive strength, it gives information on the characteristics of concrete. This strength measure is obtained through standardized crushing tests on cast cubes, the cubes are produced alongside the construction of concrete elements on site however they are not available for strength testing of existing buildings henc3e the need for non-destructive test methods. Schmidt’s Rebound Hammer is a nondestructive test which is used to assess the compressive strength of concrete using rebound index. Surface hardness test was done on different concrete mix and compared with cube compressive strength tests. The changes in one variable explained by the change in a related variable as given by the R-squared are 93.79%, 99.42%, 86.8%, 1% and 98.5% for Mix 1, 2, 3, 4 and 5 respectively. It is noted that for proper result from non-destructive tests, more than one should be implored and the model calibration should be based on actual compressive strength.
Highlights
The recent collapse of buildings under construction generated renewed interest in testing concrete in place; not for collapse investigation, but for determining whether concrete is strong enough for form stripping and structural use. It is becoming obvious how ineffective existing practice of testing the compressive strength of cubes is with respect to modern concrete construction having in mind concrete structures are built hastily because of advancement in technology and sometimes 28 days seems too long to wait for cube strength results in the face of present pace of concrete construction, more so cube strength is not always an accurate representation of the in-place strength
As for normal strength concrete, the results show that a relationship between compressive strength and rebound number is possible for high strength concrete
The main conclusions derived from this investigation are as follows: 1. As a result of the investigations empirical relations between the compressive strength of the thirty tested concretes with similar compositions and the parameters determined by the surface hardness method have been established
Summary
The recent collapse of buildings under construction generated renewed interest in testing concrete in place; not for collapse investigation, but for determining whether concrete is strong enough for form stripping and structural use It is becoming obvious how ineffective existing practice of testing the compressive strength of cubes is with respect to modern concrete construction having in mind concrete structures are built hastily because of advancement in technology and sometimes 28 days seems too long to wait for cube strength results in the face of present pace of concrete construction, more so cube strength is not always an accurate representation of the in-place strength. To ensure structural safety and reliability, all the above processes on concrete has to be accompanied with advance testing technologies [2]
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