Cement Concrete Pavement Void Identification Technology Research

With the increase of service time of existing cement concrete pavements, various diseases have occurred for many existing cement concrete pavements. One of the principal diseases is void beneath cement concrete slabs. If the void scopes extend gradually, cement concrete slabs will appear cracks and then reduce to crash. So, if there void beneath cement concrete slab, it is significant for the pavement rehabilitation to find a method to determine the size of void area.In this paper, based on operational principle of FWD and combined with the present non-destructive testing in road engineering, the distribution of deflections of cement concrete pavements loaded by FWD is calculated with the three-dimensional finite element method. In the calculation models, the Winkler foundation and multi layered elastic foundation are used respectively and shear springs model is used to simulate joint capacity of load transmit between two slabs. For the two different kinds of foundation, various results are obtained by changing the calculation parameters. Through the analysis and comparison, it can be found that different calculation parameters have different influences on calculated deflections. In the calculation parameters, the size of void and the load transfer capacity of joints have remarkable influences on calculated deflections.Based on the analysis and comparison, the difference between two deflections which correspond to the two points of a deflection basin is chosen to be the criterion of void detection according to the characteristic of deflection basin for cement concrete pavements of which there is void beneath the corner and the edge along the transversal joint. And then some parameters influencing on the criterion of void detection are analyzed in detail. Based on the results, the correlations between the area of void and the difference are obtained by the aggression analysis. The correlation can be expressed by mathematical functions, and the influences which various parameters have on the criterion of void detection can be expressed by using the correction factors. The correction factors can be determined according to measured deflections. Finally, the size of void can be estimated according to measured deflections and a new method of void detection is presented.Considering above calculation and analysis, the non-destructive tests are done on two cement concrete pavements in service and the void beneath slabs is evaluated systemically. The evaluating conclusion is compared with the results which are made by the three points aggression analysis method, which is one of widespread applied void detection methods in the world, and it can be found that the two conclusions are almost identical in determining whether there is void beneath cement concrete pavements. When the two evaluation conclusions are compared with the existent void beneath the pavements, it can be found that they are nearly coincident. Therefore it is testified that the method of void detection presented in this paper is practically feasible and effective. Compared with other existing void detection methods, the method of void detection presented in this paper is not only simple and easy in use, but can be also used to estimate the size of void. So it is valuable for guiding the pavement rehabilitation.