Characterization of hydrophobic-treated recycled paper mill sludge in bituminous materials

The experimental investigation of the performance of hydrophobic-treated recycled paper mill sludge (RPMS) incorporated into asphalt mixtures is presented in this paper. This research implements RPMS as a solid waste additive to partially replace the mineral filler in the asphalt mixture while practicing green asphalt technology. The raw RPMS required mechanical pre-treatments and its hydrophilic property was modified chemically. The hydrophobicity was assessed by Hydrophilic Coefficient, Water Contact Angle (WCA) and Scanning Electron Microscopy (SEM). The ethanol method, which involved the esterification of ethyl esters that utilized 7ml of waste cooking oil (WCO) and 50ml of ethanol, was adopted. In the Marshall mix design, RPMS was incorporated at 0.5% and 1.0% of the weight of aggregates. Conventional 60/70 PEN bitumen and granite aggregates were used. The optimum binder content (OBC) was evaluated and justified by its adsorption strength. The mechanical properties of asphalt mixtures were determined and compared with the Public Work Department (PWD) specifications. All the volumetric properties satisfied the standard specification by PWD for 0.5% modified RPMS asphalt mixture, and thus it is preferable as it also involved lower binder cost due to the lower OBC achieved.