The Method To Identify And Evaluate Void Beneath Cement Concrete Slab

One cause of unsatisfied service level and structural damages on current cement concrete pavements in China is the void beneath pavement slab. Local void beneath concrete slab on service exists objectively. Therefore, identifying the locations and detecting the scopes of void are of importance to enhance the serviceability, elongate the life span, and reduce the cost of maintenance and repair of cement concrete pavement. In this dissertation, research is conducted focusing on two aspects including the mechanism of void initiation and development, the methods of void detection and evaluation, the main conclusions are listed below:(1) Through analyzing the causes and development mechanism of void beneath concrete slab, it was found that void appear beneath pavement slab corner firstly and then transverse joint. The void will form four sides beneath pavement slab and the scope of the first plate is often bigger than that of latter slab.(2) Based on the characteristic analysis of FWD dynamic deflection basin, the method to solve the modulus of pavement structures based on the FWD load distribution coefficient was put forward. And the model of void beneath cement concrete pavement was established by using ANSYS.(3) The dissertation analyzes the effect of the load transfer capacity at joint, void conditions beneath slab, plane size of slab and testing temperature on testing deflection. Research show that the effect of the load transfer capacity at joint and void conditions beneath slab had a significant effect on testing deflection, while plane size of slab and testing temperature had no obvious effect.(4) In this paper, slab corner deflection was taken as evaluation criterion. By means of details calculation and analysis, it was found that load transfer modified coefficient of slab corner deflection can be expressed by negative exponent with increasing the load transfer capacity, and the approximate formulas between load transfer modified coefficient and load transfer capacity was established accordingly. Void coefficient (defined as the ratio of testing slab corner deflection against theoretical value) also was put forward in the paper, and the estimation method of void ratio was established by using finite element to analyze the variation of void coefficient in different void size.(5) Based on analyzing the effect of void on fatigue life, fatigue life affecting coefficient of pavement (defined as the ratio of residual fatigue life of slab with void against that of slab with no void) was put forward, based on which, the grading standard of void degree beneath pavement slab was established.(6) Through analyzing the correlation beween development mechanism of void beneath concrete slab with damage types, the estimation model of void ratio based on fuzzy analytical hierarchy process was established. Estimation void ratio of road sections can be done by means of the model and testing damage data.