The Evaluation Of Void Beneath Slab In Old Concrete Pavement

With the increase of service time of existing cement conerete Pavements,various diseases have occurred for many existing cement conerete Pavements. Void beneath slab is one of the common structural damages of the cement concrete pavement.The appearance of void is very unfavorable to the stress of the cement concrete pavement,it influence seriously the service ability and the tired life-span of the cement concrete pavement. One of the PrinciPal diseases is void beneath cemente 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, three-dimensional finite element method of cement concrete pavement in the FWD deflection under load was calculated and analyzed.In the caleulation models,the multi layered elastie foundation are used. The dynamic load use FWD load, load time was 0.03s. through the function editor ANSYS half sine wave load on the load on the model, in order to simulate the FWD load. In the analysis of the model calculations, adjustments related to the physical and mechanical parameters of the model, obtained different results, and the results are analyzed and compared. Through the analysis and comparison,it can be found that different calculation Parameters have different influences.on calculated defleetions.In the calculation Paralneters,the size of void and the load transfer capacity of joints have remarkable influences on caleulated deflections.Using the same plate two deflection difference as a measure of void index obtained by differential deflection of different parameters on the degree of influence of void, on this basis, to set a standard value for each parameter, when other parameters as the standard value, only the void size to analyze changes in a parameter, by analyzing the results using regression analysis, standard case of void size and deflection difference between, Similarly, when other parameters change, they can have a similar relationship, in order to make other parameters on the difference of deflection and deflection off air on the impact of bad link, this paper through the correction factor to the standard case of void size and the deflection difference between an amendment , which can be of various parameters on the deflection difference of links, according to the measured deflection difference on the estimated acreage of void, and the corresponding de-air identification methods and steps.