Moisture susceptibility enhancement of asphalt mixtures using phosphonylated recycled polyethylene.

摘要

Today's asphaltic concrete pavements are expected to perform better even though they are experiencing increased volume of traffic and increased loads over what has been experienced in the past. Research has indicated that the addition of polymers to asphalt binders can enhance many properties of the asphalt pavements to help meet these increased demands.;There remains a serious problem that the addition of polymers to asphalt binders generally does not address. This involves the interfacial cohesiveness of the bond between the aggregate and the binder. Some aggregates are highly hydrophilic (water-loving) while asphalt binders and most polymers tend to be very hydrophobic (water-hating). Therefore, the addition of hydrophobic polymers to asphalt does not address the issue of interfacial tension between the aggregate and polymer-modified binders in the presence of water. This interfacial surface tension in the presence of water and traffic loads could possibly, over time, contribute to stripping. Stripping is the disbonding of asphalt from the aggregate surface. The primary objective of this research was to evaluate phosphonylated recycled linear low density polyethylene's effect on the interfacial cohesiveness between the aggregate and modified binder. It was theorized that a reaction or strong charged attraction between the phosphonylated recycled linear low density polyethylene and the aggregate surface may be possible thereby reducing interfacial surface tension. The interfacial cohesiveness was evaluated by the Tunnicliff and Root Procedures for evaluating moisture susceptibility of asphalt mixtures.;A phosphonylation process was employed to place charges along the backbone of the recycled linear low density polyethylene. A preliminary study was initiated to study the effects of wet (blending polyethylene and asphalt binder) and dry processes (blending polyethylene with aggregate). When blended with binder (wet process) the modified recycled polyethylene continued to be incompatible at normal and elevated mixing temperatures and various blending times for two binders sources with various chemical modifications (base, weak acid, strong acid) of the polyethylene. Throughout this research, the polymer-binder mixtures were constantly agitated in order to prevent separation of the polymer from the binder to ensure homogeneous specimens for analysis. Next, the modified and unmodified recycled polyethylene were blended directly with two aggregate sources (dry process) prior to blending with two binder sources.;The results indicated that there was not a clear trend when analyzing the dry and wet ITS and TSR values. These differences can be explained by the different chemical composition of the various mixtures which is made up of the individual chemical compositions of the binder, aggregates, and the presence or absence of lime, which is used as an anti-stripping agent. It is important to note that modified recycled polyethylene, samples containing no lime, produced dry, wet ITS and TSR values that were significantly higher than unmodified recycled polyethylene when lime was not present. It is hypothesized that the reaction sites on the backbone of the recycled polyethylene were reacting with the aggregate sites when lime (Ca(OH)2) was not present. The P(O) groups on the phosphonylated recycled PE were reacting instead of the Calcium groups present in lime and one of the aggregate sources. This indicates that interfacial surface tension between the asphalt binder and aggregate sources can be reduced through the chemical modification of the recycled polyethylene though it may be asphalt source and aggregate source specific.