The Thermal Cracking Mechanism Of Asphalt Mixtures Based On The Contraction-relaxation Competition

Thermal cracking is one of the three major types of diseases common to asphalt pavements,which is one of the most prevalent distresses in the world.Once thermal cracking is not handled,it will inevitably induce serious secondary diseases and then cause structural damage to the road,causing huge economic losses.Thermal cracking of asphalt mixtures includes thermal contraction,low temperature relaxation and low temperature damage.A great quantity of theoretical and experimental studies on the characterization of low-temperature performance had mostly focused on characterizing low-temperature performance with low-temperature relaxation or low-temperature failure performance,resulting in incomplete evaluation of low-temperature performance of asphalt mixtures.Hence,the thermal cracking mechanism is the basis for deeply and comprehensively capturing the low-temperature performance of asphalt mixtures.In order to solve the above problems,based on the thermal cracking mechanism of asphalt mixtures,this paper had thoroughly studied the influence of environmental factors and material composition factors on the low temperature performance of asphalt mixtures.The effect of the contraction-relaxation competition relationship on its low temperature performance was clarified.The low-temperature relaxation and thermal contraction properties of asphalt mixtures were characterized,and the effects of mesoscopic composition and structure on low-temperature relaxation and thermal contraction properties were quantified in combination with the prediction model of asphalt mixtures.The thermal cracking mechanism of asphalt mixture was explained by the mathematical relationship between contraction-relaxation in the time domain and in the space domain.The contents and results are shown as follow:Considering the influence of environmental factors on thermal cracking,based on the generalized extreme value distribution model,the statistical characteristics of winter extreme climate were obtained,which was introduced into the experimental parameters.Combining environmental factors with the temperature field distribution in the pavement,the horizon depth of the research object was determined,and the relationship between the cooling rate of the environmental factors and the low-temperature performance of the asphalt mixture was established.Considering the influence of material composition on thermal cracking,the evaluation method of low-temperature performance was unified,combining with the cracking of the road surface in service..The effects of asphalt content,asphalt type and gradation structure type on low-temperature performance were studied.Based on the factors involved in the thermal cracking mechanism,the effect of the contraction-relaxation competition relationship on its low-temperature performance was clarified.Based on the theoretical relationship between viscoelastic constitutive properties and low-temperature relaxation properties,the low-temperature relaxation properties of asphalt and asphalt mixtures were characterized.The effects of viscoelastic properties and low-temperature relaxation properties of asphalt and asphalt mixtures on its low-temperature performance were analyzed.Considering the characteristics of interlocking and void distribution during aggregates,the value range of parameters in viscoelastic interlocking factors is determined with the meso-mechanics prediction model of effective complex modulus.The relationship between the model parameters and the skeleton characteristics obtained by CT was established,and the influence of mesoscopic composition and structure of asphalt mixture on low-temperature relaxation performance was quantified.The effects of asphalt types and gradation types on thermal contraction were clarified,and the effects of thermal contraction characteristics of asphalt and asphalt mixtures on the low-temperature performance of asphalt mixtures were analyzed.The meso-mechanics prediction models applicable to different grades of dispersed phase materials were selected by comparison.The prediction models of thermal contraction strain of different graded asphalt mixtures were unified,and The influence of the mesoscopic composition and structure of the asphalt mixture on its heat contraction strain is quantified.Considering the thermo-physical properties of the asphalt mixture,the relationship between steady-state heat transfer and thermal contraction strain during transient heat transfer was established.In the competition in the time domain,the thermal stress and energy accumulation process were calculated after making up for the shortcomings of the existing algorithm.The thermal stress accumulation curve is characterized by competition in the time domain.Based on the prediction of low-temperature performance based on the strength and energy as the criteria for thermal cracking,the thermal cracking mechanism in which contraction-relaxation competes in the time domain and the space domain was explained.The contraction-relaxation competition index was constructed.Based on the principle of the order of low-temperature performance of different asphalt mixtures,and based on the relationship between different indicators and low-temperature performance at different temperatures,the mathematical relationship between the competition index and low-temperature performance was established.Overall,it was pointed that the contraction-relaxation competition determines the low-temperature performance.Based on the meso-mechanical prediction method of low-temperature relaxation performance and thermal performance of asphalt mixture,the effects of the meso-composition and structure of asphalt mixture on its low-temperature relaxation performance and thermal contraction performance were quantified.The mechanism of thermal cracking under contraction-relaxation competition is explained,depending on the mathematical relationship between contraction-relaxation competition in the time domain and space domain and the low-temperature performance.