Study On Evaluation Of Concrete Strength By Ultrasonic-rebound-resistivity Method

Concrete is the indispensable engineering material in infrastructure projects.The quality control of concrete is quite important in engineering qualityinspection. Strength is the key indicator for evaluating the quality of concrete.This paper reviews the non-destructive testing technology of concrete at homeand abroad, and clarifies the significance of non-destructive testing technologyfor concrete quality control. On the basis of the ultrasonic-rebound combinedmethod, the ultrasonic-rebound-resistivity combined method is proposed toevaluate the strength of concrete. The main research contents and results are asfollowings:(1) Ultrasonic velocity, rebound value, resistivity and strength weremeasured for the standard concrete blocks of different intensity levels, of whichthe resistivity of concrete was specially studied. Compared with the directcurrent measuring method, the alternating current measuring method candecrease the influence of polarization on resistivity measurement. The resultsshow that the resistivity of the concrete block increases with the increase of theage and for the concrete blocks of the same age, the higher the strength grade is,the higher the resistivity is. The scatter plot of resistivity-strength shows thatthere is an obvious correlation between the resistivity and strength and ingeneral, the resistivity increases with the increase of strength. Furthermore, theresistivity-strength points have low discreteness, so resistivity is a suitableparameter to evaluate the strength of concrete. (2) With the measured ultrasonic velocity, rebound value, resistivity, and strength of the concrete blocks, one-parameter, two-parameter and three-parameter strength curves were established and the errors were analyzed. The strength curves of power function type generally have smaller errors compared with the results obtained by using other type functions. High accuracy strength curve was established using the ultrasonic-rebound-resistivity combined method. The function is fcuc=0.449v0.416R0.915ρ0.333and its relative standard error is only7.2%.