Experimental Study On The Morphology And Performance Of Epoxy Asphalt And Mixture During Curing Process

The epoxy asphalt mixture is widely used in steel deck pavement due to its excellent strength,high-temperature stability,fatigue durability and moisture resistance.Before open to traffic,the epoxy asphalt pavement after compacted needs to be cured for a period of time to achieve a certain strength to resist the load of the traffic.The warm mixed epoxy asphalt mixture generally requires a curing period of more than 30 days,and the hot mixed epoxy asphalt mixture generally requires a curing period of 7–14 days.The performance changes of the epoxy asphalt mixture during the curing process had not been paid attention to,which leads to a lack of specific technical index and theorey basis on the time control for the epoxy asphalt mixture pavement construction and conditions of open traffic.Therefore,it is necessary to carry out an investigattion on the performance changes of epoxy asphalt mixture and the effect of load during curing process on the mechanical properties of the mixture after fully curing.First the microscopic morphological changes and the strength growth laws of epoxy asphalt during the curing reaction process were analyzed,and the curing mechanism of epoxy asphalt was revealed;then the performance changes during the curing process of epoxy asphalt mixture were further studied;the epoxy asphalt mixture with different curing degree(hereinafter referred to as curing degree)subjected to a load was fully cured continuly,and the influence of the loading on the performance of the epoxy asphalt mixture during the curing process was evaluated.The interlayer bonding is the foundation of the integrity of the steel deck pavement structure.Finally,the effects of the curing degree of the epoxy asphalt mixture on the interlayer bonding effect were evaluated to determine the time schedule of the pavement construction.Tests were carried out to investigate the performance changes of the hot mixed epoxy asphalt and its mixture and the effects of load during the curing process,and the summery and conclutions are as follows.(1)Fourier transform infrared spectroscopy(FTIR)and tensile tests were carried out on the epoxy asphalt with different curing times to explore the strength growth law.In addition,the laser scanning confocal microscope(LSCM)and the scanning electron microscope(SEM)tests were conducted to observe the curing process of epoxy asphalt.The microscopic morphological changes were analyzed to reveal the formation mechanism of epoxy asphalt strength.The results indicated that the increase of epoxy asphalt strength was mainly based on the cross-linked network structure formation of epoxy resin.During the initial curing stage(the degree of curing was less than 30%),there was no network structure formed,and the strength was low;in the intermediate curing period(the degree of curing was between 30%–65%),the network structure was formed and gradually encrypted and hardened,and the strength increased rapidly;in the later period of curing(the degree of curing was greater than 65%),a stable network structure was basically formed.(2)The Marshall stability tests were carried out on the epoxy asphalt mixtures with different curing times to explore the strength growth law of the mixtures,and with the rutting tests and the four-point bending fatigue tests to analyze the influence of the curing degree of epoxy asphalt mixture on the anti-rutting and anti-fatigue performances.The results showed that as the curing time increased,the initial curing degree of the epoxy asphalt mixture increased rapidly,and the curing degree increased slowly after reaching 80%.In addition,it had been shown that the high temperature stability and the fatigue resistance of epoxy asphalt mixtures increased with the degree of curing.When the curing degree reached 45%,the epoxy asphalt mixture had good high temperature stability and when the curing degree was greater than 50%,it had good fatigue resistance.(3)The epoxy asphalt mixtures with different degrees of curing were applied load,and then cured fully after loading.The three points bending test and the four-point bending fatigue test were conduncted on the fully cured mixture to evaluate the effects of loading on the epoxy asphalt mixtures with different curing degrees on the mechanical properties of the mixture cured fully.The results showed that the performance the mixture with a curing degree greater than 65% was hardly affected,thus the pavement can be opened to traffic when the mixture curing degree is greater than 65%.When the curing degree was less than 30%,the epoxy asphalt mixtures could withstand a certain degree of load,and the damage could be recovered in the subsequent curing process.The mixtures with a curing degree of 30%–65% would produce unrecoverable damage after loading,which would affect the performance of mixture.(4)In order to investigate the influence of the curing degree of epoxy asphalt mixture on the bonding properties between the pavement layers,the pull-out test was conducted to observe the mesomorphology of the fracture interface between the pavement layers.The results showed that the higher curing degree of the underlying layer was not conducive to the bonding between the pavement layers,and it was suggested to complete the paving of the upper layer before the curing degree of the underlying layer mixture was less than 30%,which was helpful to the interlayer bonding strength.When the curing degree was more than 60%,the amount of the binder course could be appropriately increased to improve the bonding strength between layers.Through the systematic experiments on the performance change of the hot mixed epoxy epoxy asphalt and its mixture during the curing process,the strength growth mechanism of the epoxy asphalt and its mixture was revealed,and the mechanical properties of the epoxy asphalt mixture at different curing stages were analyzed.Furthermore,the proposeded interval time between the construction of the upper layer and lower layer of the epoxy asphalt pavement on steel bridge deck and the strength ratio of epoxy asphalt mixture for opening traffic were determined.The results can provide theoretical and technical reference for the research,design and construction time schedule control of the hot mixed epoxy asphalt pavement on steel bridge deck.