Effect of Load Pattern in the Generation of Higher Harmonic Amplitude in Concrete Using Nonlinear Ultrasonic Test

Abstract

Non-destructive testing is used in monitoring health of structures. In this paper, nonlinear ultrasonic test was done to analyze the sensitivity of the fundamental and higher harmonics with the internal damage in concrete. Good sensitivity produces significant quantitative changes in the nonlinear spectral amplitude parameter corresponding to the deviation of load. In actual conditions, structures have different design strength with varying water cement ratio. In addition, it is experi-encing loading and unloading. These are considered as major factors that induce effect in the behavior of ultrasonic test result in concrete. Past researches have only considered increasing application of load with single loading pattern. This study aims to investigate the effect of load application pattern in the generation of higher harmonics. Ordinary concrete specimens of size 150mm x 150mm x 150mm with water-cement ratio WC40 and WC60 were casted and tested using uniaxial compression machine with two load patterns: a.) single loading pattern from 0% to 100% and, b.) multiple loading/unloading pattern. Ultrasonic test with pitch-catch configuration was conducted at each loading state to record the fundamental and higher harmonic generation in the concrete.The experimental results showed that there was a good sensitivity for 3^rd harmonic amplitude parameter D_A when it was subjected to single loading pattern for both WC40 and WC60. On the other hand, good sensitivity was only observed for 2^nd harmonic amplitude parameter D_A when it was subjected to multiple loading/unloading pattern for both WC40 and WC60. This showed that the 2^nd harmonic amplitude was consistent and sensitive when repeated load was applied for low and high water cement ratio.