A COMBINED ULTRASONIC METHOD ON THE ESTIMATION OF COMPRESSIVE CONCRETE STRENGTH

The ultrasonic pulse velocity method has been used to estimate concret e compressive strength for over 40 years. However the error of the est imation is about +/-20% at 95% confidence interval even despite a spec ific calibration. This paper introduces an alternative method which co mbines the ultrasonic pressure wave velocity and relative amplitude th at can reduce error to +/-5%. The relative amplitude is basically an a ttenuation method which measures the ratio of the pressure and the she ar wave amplitudes. In developing the present combined method, about 5 00 concrete samples have been prepared for the resting of various para meters. These samples were prepared in nine different sets to cover al l the main factors that have been identified as having some effect on the strength-ultrasonic parameters relationship. The factors concerned are the effect of ageing, type and size of coarse aggregates, method and period of curing, moisture content, the existence of reinforcement bars, beam path distance and ultrasonic testing techniques. A chart f or strength prediction by the present combined method together with va rious charts for the corrections have been established. These charts h ave also been tested with several field samples. Besides a reduction o n the error oft he prediction, the method also shouts an increase in r eliability.