Analyses Of Top-Down Cracking In Asphalt Pavement With Flexible Base

Based on the structure of asphalt pavement with flexible base in china, the mechanical model of asphalt pavement structure influenced on tire-asphalt pavement interaction was set up to specify the mechanical response of Top-Down cracking and search for measures in prevention and cure Top-Down cracks.Based on the real tire-asphalt pavement contact stress, the structure and load transfer mechanisms of radial tire, tire- asphalt pavement contact area was partition to five rectangles. Based on the Poisson effect of the radial tire treads structure, tire- asphalt pavement contact stress was predigested to the vertical contact stress, the transverse contact stress(perpendicular to the tire traveling direction), the longitudinal contact stress(parallel to the tire traveling direction). Three-dimensional nonlinear models were set up in ABAQUS to simulate tire-asphalt interaction. The numerical analysis results show that the mechanical response result in Top-Down cracking in the structure of asphalt pavement with flexible base; If AC surface thickness exceed 15cm, the modulus ratios between AC surface and base less than 4, the pavement structure is beneficial to prevent Top-Down cracking; Small wheel load, more wheel number, inflation pressure between 0.6-0.8MPa and continuous interlayer Contact Conditions are advantage factors for prevention of Top-Down cracks. An exploration of relation between above parameters and Top-Down cracking with the mathematical statistics method is analyzed.Two-dimensional nonlinear models were set up in ABAQUS to simulate Top-Down low-temperature cracking of asphalt pavement with flexible base, Study on Top-Down crack fracture length and temperature drop range, The numerical analysis results show that after cooling process, asphalt pavement with microcracks cause Top-Down cracking; In cooling process, tensile stress at surface is the biggest in pavement; Mises stress and tensile stress gradually reduce with the depth increased. The longer the initial crack depth, the greater the stress intensity factor KI in cooling process, the easier Top-Down cracking. With increase cooling rate, stress intensity factor KI are rapidly increasing, Top-Down cracks develop will sooner.Based on tire-pavement contact stress, temperature, pavement structure and material properties, the numerical analysis results show that the initial of load-caused Top-Down cracks show V-Shape; Top-Down cracks which develop along Vertical direction, is fatigue cracks in the first step; In the second step, when Top-Down crack developed under the surface about 5-10cm, the direction of Top-Down cracks have a certain oblique angle with Vertical direction. At the depth of 5-10cm, Shear stress which achieve the greatest, turn into the major incentive; temperature crack is I-type crack.