Research On Induction Self-healing Properties Of Warm Asphalt Concrete

The temperature cracking and fatigue cracking can easily arise in asphalt concrete pavement due to the repeated action of the long-time vehicle load and climate environment,so timely repair and maintenance is needed.Otherwise the cracking will develop into different types of diseases,such as loose,potholes,slurry pump and so on.In recent years,an advanced idea of asphalt pavement maintenance advocated by the western developed countries is to maintain the asphalt pavement when the micro cracks appear using self-healing performance of asphalt concrete,preventing micro cracks expanding into macroscopic cracks or potholes and prolonging the service life of the pavement.A large number of studies have shown that the self-healing of asphalt concrete is highly dependent on the temperature.This paper explored the feasibility of using induction heating to enhance the self healing properties and the durability of warm mix asphalt concrete.First,the steel fibers were first optimized through researching the thermal properties,water stability,low temperature crack resistance and fatigue properties of the warm mixed conductive asphalt concrete.The testing results show that adding warm mix agent improves the fatigue life to some extent and decreases the low temperature crack resistance and the water stability of asphalt concrete,but they still meet the requirements of technical specification.Adding steel fibers can improve the conductive performance of warm mix asphalt concrete and make it suitable for induction heating,and increase its spiting strength,low temperature cracking resistance,water sensitivity and fatigue resistance.According to the mechanical properties,thermal properties and induction heating of warm mix asphalt,the steel fiber A05 among the five kinds of steel fibers is the most ideal material for induction heating The heating speed of asphalt concrete is 1.06℃/s at a heating distance of 10 mm.Then,the heating and cooling speeds,the temperature gradients at different heating distances of warm mix asphalt concrete were investigated with an infrared camera.It is found that the induction heating speed of asphalt concrete is higher when the heating distance is lower.And the induction heating speed of warm asphalt concrete is slightly lower than the hot asphalt concrete.The heating gradient of asphalt concrete is only related to the depth of the specimen,and it doesn’t change as the induction heating distance.In order to avoid the permanent deformation,a rest period of 1 hours is needed after applying the induction heating technology.Finally,the induction heating induced self healing recovery after fatigue and fracture of warm mix asphalt concrete were investigated through fatigue-healing and fracture-healing tests to determine the best self-healing temperature and the healing efficiency,and to optimize the healing parameters of the warm mix asphalt concrete.The induction healing performance of hot and warm mix asphalt concrete at different strain levels and different heating depths were compared.The following results were obtained: Warm mix asphalt concrete does not have the ability to heal the fracture strength under normal temperature,but shows very high self healing ratio with induction heating,indicating that induction heating can effectively close the cracks in warm mix asphalt concrete.The optimal healing temperature of warm mix asphalt concrete is about 75℃,and the optimal healing temperature of hot mix asphalt concrete is about 85℃.The optimal healing temperature doesn’t change as the induction heating distance varies,but the best induction healing ratio increases with the decrease of the heating distance.Excessive heating could damage the structure of asphalt concrete due to expansion,and thus reduces the induction healing rate.