Mechanical Analysis Of Asphalt Pavement Low Temperature Cracking

Thermal cracking is one of the common failure modes of asphalt pavement in coldregions, which generally occurs under the extreme low temperature condition. Most cracksare perpendicular to the longitudinal direction of the road with certain spacing. At present,researches of thermal cracking mainly focus on material properties, but few involve theeffects of pavement structure and the mechanism of uniform crack spacing. In this study,thermal stress/strain response of asphalt pavement and theoretical crack spacing wereanalyzed based on typical pavement structure and the measured temperature data in Gansuprovince, which will greatly help the selection and design of pavement material and structure.Based on the temperature data from field sections in Gansu Province, it was founded therelationship between daily temperature fluctuation and time was similar throughout the yearand pavement surface temperature fluctuation follows a sinusoidal mode. The highesttemperature on pavement surface occurred slightly after that of the air temperature. Themaximum daily temperature difference was on pavement surface. The daily temperaturefluctuation decreases as the pavement depth increases, and the pavement temperature remainsconstant beyond certain depth.Based on the theory of heat conduction，the analytical solution of temperature field wasderived for homogeneous model with vertical side slope and inclined side slope under the firstboundary condition, which was later compared with the numerical solution. The differencesamong one-dimensional model and two-dimensional model with vertical side slope andinclined side slope were analyzed. For the two-dimensional model, the effects of slopetemperature boundary conditions on the temperature distribution was within1.5m to subgradeedge, whereas the temperature distribution near the road centerline depended on the depthonly.From the thermal stress solution of Wu Ganchang, the analytical solution was derived tostudy the effects of wearing course calculated length on thermal stresses within the pavement.It was found that thick surface layer and good pavement layer bonding conditions canimprove pavement thermal cracking resistance. It was also found that asphalt pavement wasmore resistant to thermal cracking with low resilient modulus and small temperature shrinkage coefficient for surface layer.Finite element model was created to study the effects of pavement calculated length onmaximum thermal stresses and strains on pavement surface. Through parameter sensitivityanalysis, it was found that pavement model with4meters thick subgrade can meet accuracyrequirement. It was also found that the reference temperature has a critical effect on thedistribution of pavement thermal stresses and strains, and different control indexes (thermalstress and thermal strain) had entirely different requirements of layer modulus.According to linear visco-elastic theory, stress accumulation and relaxation calculationand parameter sensitivity analysis during the cooling process were performed. Thermal crackswere more prominent during severe temperature fluctuation period between seasons. Arepeated thermal loading will also lead to fatigue thermal cracking. Based on the results ofthis study, the existing asphalt pavement design method was improved with the introductionof pavement surface thermal stress/strain checking index.