| Description |
Hot Mix Asphalt (HMA) is a combination of siliceous, calcareous, or intermediate aggregates from selected sources, blended with asphalt binders from various asphalt binder producers. These components are modified by additional additives to enhance the bonding of the binders and aggregates. Concern over moisture damage (stripping), defined as the loss of strength and durability in asphalt mixtures when the binder separates from the aggregate, has prompted years of research into a variety of failure mechanisms. Prominent in these failure mechanisms is the pH at the interface of the binder and the aggregate. This dissertation addresses the pH variance of the individual components and loose blended HMA mixes from seventeen selected material sources and two asphalt binder sources to assess the pH of any chemical reactivity. The main objective is to determine if pH variances of individual components and/or mixed HMA materials (asphalt binder, aggregate and additives) point to suspect components or combinations which are causing a chemical reaction and thus instability or moisture-induced stripping at the aggregate interface. This research may point to alkali-silica and alkali-carbonate reactivity (ASR/ACR) of aggregates as potentially contributing causes of moisture-induced damage in HMA mixes. Statistical analysis is used to interpret the interaction of the independent variables and point to contributing components correlating with the pH variance and chemical reaction. With an inexpensive pH test, prior to design, suspect components could be eliminated from consideration in the design, which could then lead to improved asphalt mixtures and longer lasting pavements. |
