Combined Nondestructive Testing Method of Concrete

The purpose of the present paper is to obtain a practical expression for estimating the compressive strength of concrete using the nondestructive testing method combining rebound number with ultrasonic pulse velocity and to discuss its applicability to the evaluation of the strength of concrete members or structures. Experimental investigations are carried out to examine the effects of factors such as water-cement ratio, the maximum size and volume fraction of coarse aggregate, the curing condition and age of concrete. Accuracies of the prediction expressed in various types of empirical formulae are examined by multiple regression analysis, and practical equations for estimating the concrete strength are proposed. The equations are applied for evaluating the strength distribution in a concrete column and in an existing cocnrete building