Improvement on Recognition Method of Void beneath Slab Based on Nondestructive Testing Technologies

In preventative maintenance, it is very significant to accurately recognize the void beneath the cement concrete pavement. However, there are quite a few defects in the current nondestructive testing (NDT) technologies of void recognition. Based on ground penetrating radar (GPR), the void investigation is carried out on several typical highway sections in Anhui Province. Then, the reflected wave profile is obtained by "Reflex-Win" so as to ascertain whether there is void at the bottom of these pavement slabs. Next, falling weight deflectometer (FWD) is utilized to carry out multi-level load deflection test so that the "load-deflection" regression models can be established by the test results. Additionally, extension evaluation is adopted to recognize the void and its index system comprises the regression model's slope, intercept as well as the maximum deflection. Finally, comparing to the detection results of GPR, by way of adjusting the section domains of these indexes, the classical domains of different void status and their weight coefficients scientifically, relatively higher recognition ratio and relatively lower misjudgment ratio can be acquired. The study shows that under this improved method, the void ratio of the typical highway sections is 33%, approximately to the result of GPR (35%). Moreover, this method's recognition ratio is 88.6% and its misjudgment ratio is merely 6.1%. The superior accuracy of void recognition shows that the improved method is able to satisfy the demands of engineering detection, recognition and structural evaluation.