Effects of air voids on comprehensive laboratory performance of cold mix containing recycled asphalt pavement

Abstract

In recent decades, cold mix asphalt (CMA) has become increasingly important in the pavement construction industry. CMA differ from hot mix asphalt (HMA) in the formulation process; CMA is produced by combining unheated aggregates with or without recycled asphalt pavement (RAP) using asphalt emulsion. One of the major concerns associated with CMA is difficulty in compacting the mix in the field. Many researchers have reported that cold mixes despite of best compaction efforts can have air voids in range of 8–14%. The authors were unable to locate research that focused solely on the influence of consequent air voids in cold mixes on their performance. Thus, the strong motivation of the present study was to evaluate performance characteristics of cold mixes having wide range of compaction levels. CMA was prepared by using 60% of RAP containing slow setting emulsion. Superpave gyratory compactor (SGC) was used to compact the CMA samples at different air voids of 6, 8, 10, and 12%. Tensile Strength Ratio (TSR) is the ratio of ITS value of conditioned and unconditioned samples. The moisture damage resistivity of CMA with various air voids was determined using different conditioning procedures: 24-hour soaking and moisture induced stress tester (MIST). Soaked TSR satisfied all air voids, however the MIST-TSR(M-TSR) of CMA with 12% air voids is below the threshold value of 80%, indicating that M-TSR is more severe than soaked TSR. Flexible pavement suffers from various types of distresses, such as cracking and rutting. Hamburg wheel tracking test (HWTT) can be used to evaluate rutting and stripping potential. The lower the inflection point for stripping, the more severe the stripping in the field. This study concluded that the stripping inflection point for 8% air voids was three times more than for 12% air voids. Marshall stability and flow test was performed to evaluate the effect of varying air voids on stability, flow, and bearing capacity of CMA whereas the durability was determined using Cantabro mass loss (CML) Test. It is expected that the findings of this study will assist the researchers in understanding how the air voids in CMA affect the performance containing RAP.