A comparison of the E- value of concrete as measured by static loading and N.D.T.

Abstract

This work provides the basis for comparison between three methods for estimating the E - value of concrete. The static method, the resonance method and the ultrasonic pulse velocity method will be compared and discussed in detail. All three methods will be applied on test specimens of three grades of concrete namely C 20, C 30 and C 40 at 7 and 28 days. The static method essentially involves the measurement of strain of standard cylinders subjected to a compressive stress. The aim of the resonance method is that of establishing the fundamental resonance frequency of test specimens by setting these under vibration. The specimens used for this test will be standard cylinders, beams measuring 100 x 100 x 500 mm and beams measuring 100 x 100 x 300 mm. As statistical tests will confirm, the resonant elastic modulus does not vary significantly with the three types of specimens used. The ultrasonic pulse velocity method is the simplest and quickest method. However, as will be discussed in the dissertation, the value of the elastic modulus obtained from such method is not as reliable as that obtained from the other two methods. The same specimens used for the resonance method will be used for this test since both tests are non - destructive. The beams will finally be tested for their compressive strength and a relation between this property and the ultrasonic pulse velocity will be investigated. The relation between the static modulus obtained from the static method and the dynamic modulus resulting from the other two methods will also be discussed together with the relation between the compressive strength and the modulus of elasticity.