Determination Of The Size Of Fractured Existing Cement Concrete Pavement Slabs

To prevent reflective cracking in AC overlay, it's an important technique to impact and fracture the existing PCC slabs. The size of the fractured PCC slabs significantly influences the effect of preventing reflective cracking in AC overlay and the bearing capacity of overlay road structure. However, the specification about the size of fractured PCC slabs is mostly determined according to the construction experience, and it's lack in support of the theory analysis. With the finite element method, the stress characteristic of the fractured and overlay road structure forced by the thermal load and the vehicle load is analyzed. Finally the size of fractured PCC slabs is determined according to the results from finite element calculating.To ensure the calculation accuracy and consider the calculation efficiency, it's needed to ascertain the geometric size and the mesh precision of the finite element model. The plane size of the AC overlay and the PCC slabs is ascertained according to the normal road structures. The plane size of the enlarged foundation is ascertained with the convergence calculation. The thickness of every layer of road structure except the subgrade is ascertained according to the normal road structures. The thickness of subgrade is ascertained according to the theory of subgrade work area. The element mesh size is ensured through the plane mesh size and the number of element layers, which are ascertained with the convergence calculation.The thermal stress of the overlay road structure is analyzed, and the thermal load simulates the process of temperature dropping at low temperature. The typical structures with 5 kinds of size of fractured slabs are calculated to analysis the thermal stress characteristics. The distribution of thermal tress in the AC overlay is gotten. According to the analysis, it's certain that the impact and fracture technique is effect to ease the stress concentration in the AC overlay and to prevent the reflective cracking. The thermal stress of the overlay road structure is analyzed to got the thermal stress characteristics, with the variety of those parameters: the modulus and thickness of the AC overlay, the thickness of the fractured PCC slabs. The vehicle load stress characteristic of overlay road structure is analyzed. The load position is ascertained, before the analysis of the typical structures with 5 kinds of size of fractured slabs. According to the analysis, it's certain that the impact and fracture technique is effect to reduce the probability of shearing type reflective cracking, but it's harmful to the load bearing capability of the road structure, causing larger deflection of the pavement. The load stress of the overlay road structure is analyzed to get changes of the load stress characteristics, with the variety of the thickness of some road structure layers.Finally educe the effective method to ascertain the reasonable rang of the fractured PCC slabs of overlayed road structure with different structural parameters, according to the comprehensive evaluation of the thermal stress and load stress of the road structure, with the main indexes: the stress characteristic of the AC overlay and the deflection of the pavement, and considering the pressure resistance of the base.