Effect of High RAP Content on Marshal Performance of Hot Asphalt Mixture for Surface and Binder Layers

Abstract

Recently, the exhaustion of new aggregates and the rising price of " raw materials" have caused the increasing exploitation of "reclaimed asphalt pavement "(RAP) in pavement construction and rehabilitation. It is being reported that the usage of RAP does not only reduce the cost of pavement construction projects due to the less consumption of asphalt and aggregate but also saves land resources and greatly protects the environment, Where the same materials used in the construction of the original highway system can be reused to rebuild, repair and maintain it. Where appropriate, recycled Aggregates and other highway construction materials make a good economy; in the" environmental and engineering' sense, with supply limited and demand increasing, HMA producers have begun the use of "Reclaimed Asphalt Pavement" (RAP) as a value component of the" HMA." For this reason, there is renewed interest in increasing the amount of RAP used in hot mix asphalt (HMA). Although many factors affect the use of RAP in asphalt paving, the two main factors are "Economic savings " and " Environmental benefits." RAP is a useful alternative to raw materials. It reduces the use of virgin aggregates and the amount of "virgin asphalt binder required HMA productions, this study highlight how RAP impacts environmental and economic terms through the use of different percentages of RAP (10, 15, 20, and 25%) from the total weight of the mixture for the surface layer, and the change of (30, 40, 50, and 60%) of the total weight of the mixture for the binder layer used in the "HMA-RAP" composition that was heated at a temperature of “150°C” and then mixed with a total temperature of “170-180°C” plus asphalt at a temperature of “153°C” so the new mixing temperature, obtained at “148- 153 ° C" to obtain the ideal recovery of the reclamation, where the asphalt binder is restored rheological properties as this temperature is considered the recovery point of the asphalt binder. The results of mixing different ratios of RAP in the hot mixture showed that a large amount could be mixed in both layers and does not exceed (20%) in the surface layer and (50%) in the bond layer. This is because the Marshall stability was the highest possible during these ratios. As for increasing or decreasing these ratios, it led to a decrease in Marshall stability. The test results showed that with the increase of the amount of RAP in the mixture asphalt, the optimum value of the asphalt level (OAC) included in the asphalt mixture decreased as the percentage of asphalt used in the surface layer was reduced from (4.9 to 3.92%) When adding 20% of the RAP, and (4.6 to 2.3%) When adding (50%) of the RAP for the binder layer. This, in turn, leads to a decrease in the cost of asphalt, which is included in the asphalt mixture, and the results showed that the mixture stability to the influence of water, changes in temperature, and bonds between new materials (asphalt and aggregate) with RAP material was still good.