Environmental Impacts Evaluation Of Hot In-place Recycling Of Asphalt Pavement

Hot in-place recycling?HIR?is deemed as a promising maintenance strategy due to its remarkable economic and society benefits,which has been widely used in the maintenance and rehabilitation of highway infrastructure.Abudant researches have been carried out on the methodology of recycling and technology,however,little has been devoted to evaluate the environmental impacts originating from the construction process.Hence,the objective of this paper is to construct an evaluation system,which can realize the process of calculating the enenrgy consumpation and emissions,estimating the environmental impacts and optimizing the decision-making process,in order to promote the quantitative analysis and environmental impacts evaluation in HIR.Firstly,the calculation model was developed based on the NONROAD model and the corresponding environmental parameters.Ezstrobe was employed as the discrete event simulation software to simulate and characterize the construction process of HIR.Two different HIR methods,remixing generation method?A?and repaving generation method?B?,were used as the research objectives to study and estimate the environmental impacts.The results showed that 1)when the paving weight was one metric ton,the emissions of all the pollutants in A were more than the results in B by19%-21%;2)when the paving length was one meter,the emissions in A were less than the results in B by23%-26%;3)the emissions emitting from the paving process were much higher than other processes,e.g.transportation process,heating process and compaction process,etc;4)the main difference between two methods in emissions was reflected in the transportation process;5)the optimal number of dump trucks in A and B were2 and 3,respectively.Secondly,three most important air pollutant-related issues,global warming,acid precipitation and respiratory effects,as well as energy consumption were selected to evaluate the environmental impacts of HIR in different working conditions.Those impacts were expressed by energy consumption?EC?,global warming potential?GWP?,acidification potential?AP?and respiratory effects potential?REP?,respectively.It could be found that the greatest environmental impacts of the whole construction processes was the GWP and the CO₂emissions was the main factor resulting in the greenhouse effect.Besides,the AP had closer relationship with the transportation condition.The overall environmental impacts of A and B could be reduced 11.6%and 14.1%through the optimized measures.Lastly,a multi-objective optimization model was constructd with the decision variables of environmental impacts,cost and construction quality in this paper.The NSGA-II algorithm was employed to solve the multi-objective optimization problem,which could obtain 20 sets of Pareto optimal solutions.Compared A and B,it could be seen that A had higher construction reliability.However,B had better environmental and economic benefits.When the extreme goals were desired,although the A and B had no relative advantages and disadvantages in the cost standard,B could get higher construction quality and better environmental benefits.This study will spur the progress of the theoretical and quantitative evaluations of environmental impacts of HIR and quatify the environmental impacts in different conditions.And it can also provide a better guidance for the decision-making process.