The strength formation process and composition mechanism of emulsified asphalt cold recycled mixtures were analyzed.The measures to improve the strength of emulsified asphalt cold recycled mixtures were summarized from four aspects,including addition of additives,optimization of binding materials,improvement of design methods and construction processes,and reclaimed asphalt pavement(RAP)pretreatment.The enhancement mechanism and improvement effect of various measures were analyzed and compared.According to the problems and characteristics of various measures,corresponding application suggestions were put forward,and future research directions were foreseen.Analysis results show that the addition of additives to enhance the strength has been relatively well studied,followed by the optimization of binding materials,and less research has been done to improve mixture design methods and construction processes,as well as RAP pretreatment,however,these aspects have promising applications for increasing the strength of the mixture.Among the additives,cement is the most commonly used and systematically studied,and its enhancement effect is better than that of lime,but too high cement content will lead to insufficient crack resistance at low temperatures.Volcanic ash material also suffers from this problem and has more impurities.Fiber has a more balanced improvement effect,but is affected by the type,doping amount,adding order,and other factors.Regenerating agent can improve durability,but is not favorable for early strength.In terms of binding material,the slow cracking nature of emulsified asphalt contributes to the overall strength,high viscosity and fast setting are beneficial to early strength,and the doping amount should be moderate and recommended at 3.5％-4.0％.Modified emulsified asphalt should be selected according to specific climatic and environmental conditions.The mixture design methods and construction processes are mainly improved in terms of the aggregate,moisture content,structural layer thickness,mixing sequence,and compaction and curing methods,with a slight strength enhancement effect,which can be used as an additional improvement condition.The trend of using large amounts of RAP makes RAP pretreatment technology more important,which currently focuses on four aspects:reduction of agglomeration rate,grading classification,strict control of RAP storage conditions,and chemical modification of RAP surface.Future research should be conducted in the following aspects:further clarifying the interaction mechanism between volcanic ash materials and emulsified asphalt to determine the optimal doping amount and remove impurities,exploring the joint application of different additives and different modifiers in improving the strength of the mixture,investigating the improvement effect of multiple enhancement measures according to the strength formation mechanism to obtain a balanced system of strength enhancement measures,focusing on the pretreatment means of RAP,and exploring the enhancement mechanism and effect of RAP surface physical properties pretreatment on the strength of emulsified asphalt cold recycled mixtures.11 tabs,11 figs,89 refs.
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NSTL
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