Research On Cracking And Fatigue Resistance Of Compounded In-Situ Hot Recycled Asphalt Mixes

In recent years,the technology of in-situ thermal regeneration has been widely used in road maintenance projects due to its advantages of environmental protection,cost savings,and fast construction.However,due to the fact that the composition of the recycled asphalt mixture is more complex than that of the fresh asphalt mixture,in the process of pavement operation due to load,climate,and many other factors,the recycled pavement is easy to fatigue damage,and its long-term durability has not been fully confirmed.In this paper,based on the in-situ hot regeneration maintenance project of the G65 motorway in Guilin,Guangxi,the proportion design of the compounded in-situ hot regenerated asphalt mixture is carried out first,and then the crack resistance,fatigue performance,and fatigue self-healing performance of the compounded in-situ hot regenerated asphalt mixture are investigated by a semi-circular bending test and a four-point bending fatigue test,aiming to provide a reference for the application of regenerated pavement.The main research contents and conclusions of this paper are as follows:（1）The old asphalt mixes milled in situ were recovered,and their properties were measured to determine the old aggregate gradation,old asphalt content,and their degree of aging in the RAP.On this basis,the Marshall design method was used to design the in-situ hot recycled asphalt mixes,and the road performance tests were carried out on the mixed in-situ hot recycled asphalt mixes with aromatic regenerants and new regenerants（waste bio-oil and surfactants,respectively）.The results show that the high temperature,low temperature,and water stability of the two types of in-situ hot recycled asphalt mixtures meet the specification requirements and can be tested for subsequent cracking and fatigue resistance.（2）The effects of different cutting depths,temperatures,regenerant types and their dosing levels,and interface enhancers on the fracture toughness K_IC,fracture toughness J_IC,and reference fracture energy were investigated by semicircular bending tests.The results showed that:1)Compared with the aromatic regenerant,the crack resistance of the new recycled in-situ asphalt mixture was the best,and the optimum dosage was 5%.2)The interface enhancer had a positive effect on the crack resistance of the recycled in-situ asphalt mixture,and the three crack resistance evaluation indexes increased to different degrees after spraying the interface enhancer.3)When the temperature was high,the toughness of the recycled in-situ asphalt mixture increased.The fracture resistance is weak at 15°C;K_IC,J_IC,and benchmark fracture energy reach their maximum values at0°C;the fracture resistance is the best;and the fracture resistance is the worst at-15°C.4)The depth of cut directly affects the fracture energy of the in-situ hot recycled asphalt mixture,and the fracture energy decreases significantly as the depth of cut increases.The fracture energy decreases significantly with increasing depth of cut.（3）Four-point bending fatigue tests were carried out on the recycled in-situ mix at different strain levels（300με,400με,600με）.The results show that:1)for the same type of recycled in-situ asphalt mix,the initial stiffness modulus decreases and the phase angle increases with increasing the amount of recycler,while the fatigue life increases and then decreases.The fatigue performance of the new recycled in-situ asphalt mixes is better than that of the aromatic recyclers due to the surfactant content.2)The interfacial enhancers can improve the fatigue performance of the recycled in-situ asphalt mixes,and the advantage is more obvious at high strain levels.3)The cumulative dissipation energy and fatigue life of different recycled in-situ asphalt mixes This relationship is not influenced by the type and amount of recycler or whether the interface enhancer is sprayed or not.The fatigue equation expressed by the cumulative dissipation energy is obtained through regression analysis,which provides a basis for the analysis of the fatigue performance of the hot recycled in-situ asphalt mixes.（4）The effects of healing temperature,healing time,and interfacial reinforcement on the recovery rate of fatigue life and the recovery rate of modulus of stiffness of the hot recycled in-situ asphalt mixes were analyzed using the"fatigue-healing-re-fatigue"test method.The results show that the healing time and interface enhancer have a positive effect on the self-healing ability of the hot recycled in-situ asphalt mixture,while the healing temperature can only improve the self-healing ability of the hot recycled in-situ asphalt mixture within a certain range.