Evaluation of the extent of HMA moisture damage in Wisconsin as it relates to pavement performance

Abstract

The objectives of this study were to evaluate the relationship between the performance of asphalt pavements in the field and the Tensile Strength Ratio (TSR) values measured in the laboratory on the original asphalt mixtures used in constructing the pavements. In addition, the study included evaluating the effects of anti-stripping additives on field performance and their impact on the cost of the production and construction of the pavements. To assess the moisture damage problem in the field, a total of 21 existing Wisconsin Department of Transportation (WisDOT) pavement sections that were built to meet the specification, prior to 1992, when the requirement of the TSR parameter was adopted, were selected to cover a wide range of locations and aggregate sources. The TSR data and the Pavement Distress Index (PDI) for these projects were collected from the TSR database and the WisDOT Pavement Management Database, respectively. Analysis of these data indicated that there is no relationship between TSR and the field pavement performance as measured by the PDI reported in 2001. In addition, there was no relationship between the TSR and specific pavement distresses that are known to be related to the moisture damage (surface raveling and rutting). To evaluate the effect of using anti-stripping additive, a database study and a laboratory study were conducted. Results from the database showed that there is an effect of using anti-stripping additives on the pavement performance (as measured by PDI) and also an effect on the specific pavement distresses that are related to the moisture damage (surface raveling and rutting). In the laboratory, the anti-stripping additives were mixed with an asphalt binder, and the changes in binder properties were evaluated. Anti-stripping additives were not found to change the rheological properties of asphalt binders, nor to improve the rutting and fatigue related properties of asphalt binder as measured by the dynamic shear rheometer (DSR). However, they were found to increase the adhesion of asphalt binder to selected mineral surfaces, especially when the binder bond is exposed to water. The cost estimation of the pavement with anti-stripping additives is found very similar to the cost of the pavement without anti-stripping additives when taking into consideration the cost of maintenance every 5-6 years of the pavement service life. The recommendations from this study include considering either improvement of the TSR test or replacing the TSR procedure with other easier, less costly procedures. The improvement of the TSR testing protocol is needed to control the excessive variability that occurs during the standard procedure. Such improvements could lead to better quantifiable test and better correlation to the field pavement performance. It is further recommended that for a better assessment of causes and consequences of moisture damage of asphalt mixtures, the role of asphalt binder and aggregate should be studied separately by using adhesion and cohesion testing.