Stone Matrix Asphalt (SMA) and pH Instability Shown on Hamburg Wheel Tracker Test Failures of SMA - Case Study

Associate Professor, Department of Construction Technologies, Utah Valley University, USA

*Corresponding author: James Allen Cox, PhD, PLS, Associate Professor, Department of Construction Technologies, Utah Valley University, 800 West University Avenue, Orem, Utah 84058, USA, Phone: 8018851741, E-mail: [email protected]

Received Date: May 20, 2025

Publication Date: June 30, 2025

Citation: Cox JA. (2025). Stone Matrix Asphalt (SMA) and pH Instability Shown on Hamburg Wheel Tracker Test Failures of SMA - Case Study. Material Science. 7(1):40.

Copyright: Cox JA. © (2025).

ABSTRACT

Stone Matrix Asphalt (SMA) is a combination of igneous, metamorphic and sedimentary aggregate materials from various sources blended with asphalt binders and mineral fillers. These components are sometimes modified by various additives to enhance the bonding of the binders and the aggregates. Concern over failed Hamburg Wheel Tracker tests of strength and durability in the Stone Matrix Asphalt mixtures prompted research into what failure mechanism is being experienced on these projects. One of the six stripping mechanisms in these failures is the pH at the interface of the binder and the aggregate. This research will assess moisture damage or stripping associated with pH instability of the individual components of a loose blended SMA mix with other types of tests associated with the corresponding material sources. The main hypothesis is that pH of the mixed components of binder and aggregate may be an indicator of potential early stripping of the binder from the aggregates. On a production level, those binder-aggregates mixes high in pH could indicate a potential for failure by any number of adhesion theory failure mechanisms that weakens the bond between the asphalt binder and the aggregate causing the SMA to fail in the field. One failure mechanism found in concrete (alkali-silica reactivity of the aggregate) could be a contributor in SMA mixes and will be appraised in this case study. The study of the failed SMA mixes may support this possibility. To accomplish this case study, the following will be addressed:

• A review of the two project mix designs and test failures

• Tests of pH were conducted on the aggregate source, of prepared loose mix and additives to be used in the SMA mixes.

• An assessment of only a limited number of Hamburg Wheel Tracker test data of the SMA placed on the project as well as the gradations, densities and oil content to determine which components are contributing to the failures.

• The results of this research will be compared with my dissertation research paper on the pH of aggregate sources in Utah.

Such research would be a resource to any department of transportation and any contractor in selecting appropriate binder and aggregate combinations to ensure the SMA mixes will result in a longer lasting, quality pavement.

Keywords: Aggregates, Asphalt, pH Instability or Reactivity, Hamburg Wheel Tracker Test Results, Moisture Damage or Stripping, Adhesion or Bond