Study On The Mechanism Of The Influence Of Low Temperature Storage Of Asphalt On Its Performance

The low temperature cracking of asphalt pavement is caused by the long-term low temperature of asphalt pavement in the service process,which leads to the serious loss of anti-cracking performance of asphalt.When the external temperature changes,the asphalt binder can’t show good viscoelastic performance,resulting in shrinkage cracks of asphalt pavement.The low-temperature crack resistance of asphalt pavement mainly depends on the low-temperature tensile deformation performance of asphalt binder.However,the traditional BBR test is too general to evaluate the low-temperature performance of asphalt binder.One hour of low-temperature constant temperature curing time is not enough to fully investigate the effect of physical hardening on its crack resistance.The experimental results will seriously overestimate the low-temperature crack resistance of asphalt material Engineering application will cause early cracking of asphalt pavement and other diseases.Therefore,it is of great value and significance to consider the physical hardening of asphalt materials in continuous low temperature environment for a more comprehensive investigation and evaluation of low temperature road performance of asphalt.Based on this,the low temperature performance of asphalt binder with different storage time at constant temperature was evaluated by ex BBR.At the same time,the thermal behavior of asphalt before and after physical hardening was analyzed by modulated differential scanning calorimetry(MDSC).The main conclusions are as follows(1)There is physical hardening phenomenon in asphalt materials under low temperature environment for a long time,which is the fundamental reason for the deterioration of low temperature properties of binder.When BBR test is used to guide the asphalt materials used in pavement engineering,the influence of physical hardening on the service life of asphalt binder is not fully considered,which is obviously not in line with the actual situation of pavement service.This kind of misjudgment in design can easily lead to early cracking of asphalt pavement.It is good to predict the low temperature performance of asphalt pavement by using ex BBR test and low temperature grade loss index In order to avoid the inconsistency between the design and the actual situation.(2)A long time of low temperature environment will make asphalt binder hard and brittle.In the early stage of low temperature,the hardening rate of asphalt binder increases rapidly,and in the later stage,most of the low temperature grade loss also occurs in the early stage of physical hardening.At the same time,in the early stage of low-temperature physical hardening,the failure temperature of asphalt binder is mainly controlled by creep stiffness S.with the extension of constant temperature storage time,the creep rate of binder becomes the controlling factor of low-temperature failure temperature.(3)The change of asphalt state in the process of heating goes through such a process as glassy state,high elastic state and viscous flow state,which is caused by the solid-liquid transformation of its internal components.After the physical hardening of asphalt,the cohesional entanglement occurs in the asphalt system.The increase of cohesional entanglement nodes inhibits the movement between molecules,thus reducing the viscoelasticity of the material.With the extension of low temperature hardening time,the cohesional entanglement of the internal components of the material continues to increase,and the macroscopic performance is that the polymer becomes hard and brittle.(4)The number of endothermic peaks increases,the position of TG moves forward,and the long-time low-temperature hardening makes the aggregate state transition in a wide temperature range.Different components have phase transition in a smaller temperature range,forming a stable low-energy state.When it needs to complete the transition from glassy state to viscoelastic state,it needs more energy than unaged asphalt.And because the entanglement nodes of molecular chains are formed by different components,and the melting points of different components are not consistent,so there will be many smaller signal peaks in the original larger temperature range during the heating process.This is the reason why some asphalts have multiple glass transition temperatures after physical hardening.