Research On Cooling Law Of Hot Asphalt Mixture Paving

The heat of hot asphalt mixture is continuously lost to outside during paving,and its temperature decreases gradually.On the one hand,the temperature of mixture decreases suddenly under the unfavorable construction conditions such as low temperature or strong wind,which leads to the urgent effective compaction time,and the paving has not been completed,but the temperature of mixture has been reduced below the minimum rolling temperature.On the other hand,low paving temperature will cause insufficient compaction or segregation of the mixture,which will affect the pavement performance.Therefore,road researchers have to understand the cooling law of mixture in paving stage,according to the temperature decreasing,decide whether to select corresponding means or delay the cooling rate from which aspects to ensure the compaction effect.According to the above problem,the study carried out the following work.First of all,based on the theory of heat transfer,the modes of heat transfer of mixture in paving stage were determined,and the internal and boundary heat transfer modes of asphalt mixture were described mathematically.The physical model of thermal diffusion of mixture paving had been constructed,and the factors of thermal diffusion of mixture paving had been determined according to the physical model.Secondly,the finite difference method was used to list several algebraic equations of the paving temperature field including spreading layer and underlying layers,then by using the method of simultaneous equations and relying on MATLAB mathematical software,the system of algebraic equations had been written into program code and called reasonably,so the simulation model of paving temperature field under concrete paving conditions had been constructed.The simulation temperature values are compared with the measured temperature values,and results show that the simulation model is generally accurate and credible.Thirdly,the factors of thermal diffusion of asphalt mixture paving were divided into environmental conditions,spreading layer conditions and underlying layer conditions.The orthogonal experiments of three kinds of factors were carried out based on the simulation model whose accuracy was verified and the orthogonal experiment design method,and then the sensitivity of factors in their classes were analyzed by multivariate variance analysis of SPSS statistical software.Results show that the order of influence degree of environmental factors is air temperature-surface temperature,wind speed,solar radiation and effective radiation,the order of spreading layer factors is thickness,mixture type,spreading temperature,and aggregate type in mixture,and material type in underlying layer conditions has certain influence on paving thermal diffusion.Fourthly,by using the orthogonal experiment design method,all the factors of paving thermal diffusion were compiled and the simulation orthogonal experiments were carried out again.A multiple regression prediction model of paving temperature had been established using the data of the above experiments and SPSS statistical software.The multiple regression prediction model of paving temperature was used to write code in the MATLAB graphical user interface(GUI),and an application had been produced that could be run separately to predict the real-time temperature of mixture paving.Results show that the multiple regression prediction model established by factors of paving thermal diffusion and stepwise analysis method is fit effectively and the regression equations are statistical significant.Mixture paving temperatures are predicted more easily by incorporating the multiple regression equation of paving temperature into the MATLAB GUI program and designing the interface of the application.The purpose of this study is to explore the cooling law of hot asphalt mixture paving,in which the method and approach of constructing simulation model of paving temperature field widen new thought that calculate mixture paving temperature by discrete equations in terms of energy.The application predicting mixture paving temperature is on a degree of valuable for predicting real-time mixture temperature in engineering practice.