Reducing susceptibility to moisture damage in asphalt pavements using polyethylene terephthalate and sodium montmorillonite clay

This study examines the feasibility of developing built-in resistance against moisture damage using either passivation or an arresting mechanism. A specific moisture-susceptible paving mixture with proven moisture-damage issues in the field was selected for this study. The damage was attributed to failure at the interface of bitumen and stone aggregate due to accumulation of acidic compounds at the interface with subsequent dissolution in the presence of water. Here, we examine two remedial methods. The first method introduces a polyethylene terephthalate based additive (PET) to bitumen to neutralize active sites of stones with concentrations of silica oxide greater than 50% (denoted simply as siliceous stones), suppressing nucleation and growth of acids at the interface. The second method introduces sodium montmorillonite clay (MMT) to adsorb acids and prevent their migration to the interface of stone and bitumen. Measurement of shear binding between siliceous substrates and bitumen using a shear rate sweep test showed increases of 21% and 43% due to the inclusion of MMT and PET, respectively. This improvement was also observed in the results of bitumen bond-strength tests performed on glass and on stone substrates. Results of the evaluation at the mixture level using a Hamburg wheel-tracking test showed that the addition of MMT and PET improved resistance to moisture damage, as evidenced by the increasing number of cycles before moisture stripping occurs. For the PET-modified mixture, no stripping inflection was observed until 20,000 cycles. It was also observed that MMT's adsorption of acidic compounds from bitumen led to the appearance of surface dents after water conditioning. The PET-modified specimen showed some signs of color change after water exposure, without any signs of stripping. The study results help formulators design materials with built-in resistance mechanisms against moisture damage.