Serviceability during asphaltic concrete production and leaching concerns of asphalt mixture prepared with recycled paper mill sludge

The performance of an asphalt mixture does not only rely on its engineering properties. Yet, the service characteristics of an asphalt mixture do play an important role on the durability of pavements. This study was conducted to evaluate the effect of different aggregate types (granite and limestone) and the incorporation of recycled paper mill sludge (RPMS) on mixtures behaviour in terms of workability and compaction energy index (CEI). The effect of RPMS incorporation on the leaching potential was also assessed. A test was evaluated through the toxicity characteristics leaching procedure (TCLP) to identify the leaching behaviour of heavy metals with a possibility to contaminate the nearby water sources. Next, a surface morphological analysis was also conducted through the Scanning Electron Microscopy (SEM) to assess the relationship of fillers addition to the optimum binder content and water absorption. In this study, RPMS was used at rates of 0.5% and 1%. Based on the TCLP’s results, the leaching potential of RPMS incorporated mixture was addressed and proven to be less than the standardised requirements. The addition of different percentages of RPMS into limestone and granite asphalt mixtures had resulted in the increment of optimum binder content; however, still lower than control samples. Whereas their small increment in the combined water absorption percentage are relatively same to the control samples. The workability indices of asphalt mixtures peaked upon the usage of 0.5% RPMS but slightly reduced at 1% RPMS but nevertheless remained higher than the control specimen. This is due to the ability of RPMS reduce the surface tension, hence enabling less energy for compaction. The 0.5% RPMS addition was found to be the optimal content required to obtain a better service performance of asphalt mixture during mixing and compaction processes.