Study on Refined Crushing Technology of RAP and Mechanical Properties of RAP-Doped Cement-Stabilised Macadam Base

In order to study the effect of the crushing process on the fine separation of reclaimed asphalt pavement (RAP) and the mechanical properties of cement-stabilised aggregate mixed with RAP, four crushing processes, namely small mesh hammer crushing, hammer crushing, jaw crushing, and double roller crushing, were used to separate the aggregate from asphalt in RAP materials. The effect of crushing on the grading characteristics and agglomeration condition of RAP material was investigated. RAP cement-stabilised aggregates were prepared and analysed for their mechanical properties and micro-morphology using RAP materials obtained from fine separation. The relationship between the RAP material properties and the mechanical properties of the RAP-added cement-stabilised aggregate was analysed on the basis of the tests. The results showed that crushing breaks down large-size RAP materials, leading to grade refinement, and that hammer crushing was the most effective in reducing the grade variability. The highest agglomerate dissociation rate of RAP material above 4.75 mm after small mesh hammer crushing treatment was 96.9%, and the residual mass ratios of RAP material in two grades of 0~3 mm and 3~5 mm after hammer crushing were lower than 90%. The unconfined compressive strength, splitting strength, and compressive resilience modulus of RAP cement-stabilised aggregate after crushing were greater than those of the uncrushed RAP cement-stabilised aggregate, and the crushing increased the amount of RAP in the mix to 60%. Compared with the unadulterated RAP cement-stabilised aggregate, the hydration products of the RAP cement-stabilised aggregate were reduced after crushing, and there were obvious gaps and discontinuities between the RAP material and the cement paste. The RAP gradation and agglomeration condition correlated strongly with the mechanical properties of the mixes, with RAP coarse aggregate agglomerates being the main cause of gradation variability. This paper provides theoretical support for the proposal of a pretreatment process to reduce the variability of RAP-doped cement-stabilised aggregate and improve the mechanical properties, and the research results are conducive to the recycling of high-volume RAP materials in the base.