Evaluation Of Environmental Effects Of Recycled Aggregate Asphalt (Cement) Concrete From Construction Solid Waste Based On Life Cycle Assessment

In view of the current lack of research in the analysis and calculation methods for the environmental evaluation of recycled aggregate asphalt mixes and recycled aggregate cement concrete.Based on the basic needs of China’s high-quality economic development at the present stage,this paper adopts a combination of theoretical research,data statistics and example analysis.Specifically,based on the life cycle assessment（LCA）theory,taking construction solid waste recycled aggregate as the starting point of the study,and then the environmental impact assessment models of the whole life cycle for recycled aggregate asphalt mix and recycled aggregate cement concrete are established respectively.The research contents and conclusions are as follows:（1）Using three environmental impact factors of energy consumption,carbon emission and land occupation as evaluation indexes,we conduct a comprehensive evaluation of the environmental impact of the whole life cycle under two treatment methods of construction solid waste.The results show that 1 t of waste concrete directly landfilled will generate 61.38 MJ of energy consumption,18.52 kg of carbon emission and 0.24 m² of land occupation,while the recycling of recycled aggregates will generate 74.21 MJ of energy consumption,28.71 kg of carbon emission and 0.005 m²of land occupation.（2）Based on LCA theory,the life cycle of recycled aggregate asphalt mixes was divided into three stages:raw material production,transportation and mix preparation.By controlling the replacement ratio of recycled coarse aggregate（i.e.,0%,20%,40%,60%,80%and 100%,respectively）,the changes of six environmental impact indicators of GWP,ODP,POCP,AP,EP and CED in its whole life cycle were investigated.It was found that with the increase of recycled coarse aggregate replacement ratio,the six environmental impact indicators of 1 t of hot mix AC-20 recycled aggregate asphalt mixture were gradually reduced.Furthermore,ODP,POCP and AP have the most obvious decrease,reaching more than 70%,but EP has the least obvious decrease,less than 5%.（3）Based on LCA theory,the life cycle of recycled aggregate cement concrete was divided into six stages:raw material production and transportation,recycled concrete preparation,transportation,construction,and demolition.Considering the effect of carbonation of recycled concrete,a sensitivity analysis model was established to investigate the effects of water-to-cement ratio,aggregate replacement ratio and transportation distance on its life cycle carbon emission.The results exhibit that the higher the replacement ratio,the better the carbon sequestration effect of recycled aggregate cement concrete and the lower the life cycle carbon emissions under the same water-to-cement ratio.In addition,the carbon emissions in the raw material production stage account for 80.92%～85.62%,which mainly originate from the fact that a large amount of CO₂ is generated during the cement calcination production process.