Study On Design Method For Asphalt Overlay On Old Cement Concrete Pavement

Paving asphalt pavement on the old concrete pavement is a common effective technique for pavement renovation. It has the advantages such as short construction period, little influence on transportation and good service after renovation. So it has been the common measure to improve the pavement performance. But during the using of asphalt overlay, it easily emerges the reflective cracking in asphalt concrete pavement, and this brings negative influences on the life of pavement. So how to delay and restrain reflective crack is the key to the design method for asphalt concrete overlay on the old cement concrete pavement, which is also a crux. At present, all of the design methods for asphalt concrete overlay at home and abroad are not perfect, and there is not yet an accepted reasonable and feasible design method. In this paper, on the basis of previous studies, considering the reflective cracking, the design method for asphalt concrete overlay on the old cement concrete pavement is further discussed and explored.The design method for asphalt concrete overlay on the old cement concrete pavement involves not only the damage of old road, structural conditions, traffic conditions, environmental factors, but also reasonable mechanical analysis model, the correct material parameters and effective measures to preventing reflective cracking, and so on. The factors involved are very extensive, complex and dynamic. The paper started with the investigation and assessment of the old road, established a comprehensive evaluation system for old cement concrete pavement, which includes two aspects: pavement application performance and structural performance including six index, in order to identify the sections to be reconstructed and the treating programs, as well as to provide a basis and some data for the asphalt overlay design. The paper compared and analyzed several relatively matured design methods to propose some aspects worthy to being learned or need to be improved.Apply a three-dimensional finite element analysis program to compute the mechanical response of asphalt overlay with geosynthetics interlayer under the action of load, analyze the influence of parameters like asphalt overlay thickness, asphalt overlay modulus, old cement concrete pavement modulus,geosynthetics modulus, foundation modulus on the stress and deflection in the bottom of asphalt overlay.Through the comparison and analysis on the design concepts and design methods for asphalt concrete overlay on the old cement concrete pavement at home and abroad, on the basis of the analysis of the finite element simulation, according to the failure mechanism of asphalt overlay, the paper proposed four control indexes: cement concrete pavement slab bending tensile stress; tensile stress in joint area at the bottom of asphalt overlay under the most disadvantaged loading; shear stress in joint area at the bottom of asphalt overlay under the most disadvantaged loading; the deflection difference of both sides of joint at the bottom of asphalt overlay under the most disadvantaged loading, and finally established a anti- reflective crack-based multiple indexes design method for asphalt concrete overlay on the old cement concrete pavement.The paper is supported by the 2006 technology project of Chongqing Municipal Construction Committee"Chongqing urban road pavement reconstructing technical specifications".