Effect of Percentage Baghouse Fines on the Amount of Antistripping Agent Required to Control Moisture Sensitivity

Abstract

Moisture damage in asphalt pavement reduces the service life of the pavement as well as increase permanent deformation. Moisture sensitivity in asphalt concrete mixtures is often associated with high concentrations of fine aggregate particles. In this study, the effects of baghouse fines, a source of fine mineral aggregate, on moisture sensitivity were examined. Two types of baghouse fines with different gradations were used in various concentrations in the laboratory production of hot-mix-asphalt samples. To determine the effects of the various baghouse fines contents, testing was performed to determine the tensile-strength-ratio of the different mixes.

In order to prevent moisture damage in asphalt pavements, additives are often used to alter the interaction between the asphalt binder and the mineral aggregate. These additives can change the molecular charge of the binder or reduce the viscosity of the asphalt cement. In order to determine the effectiveness of the anti-strip additive in preventing moisture damage, the tensile-strength-ratio was also determined for specimens containing various additive and baghouse fines contents. The results of the tests showed a reduction in retained strength for the specimens without additive as compared to the specimens containing additive, demonstrating the effectiveness of the additive in preventing moisture damage.

To assess the rutting resistance of the various asphalt mixtures, an Asphalt Pavement Analyzer test was performed. Half of the laboratory compacted specimens were moisture conditioned and tested submerged, while the other half was tested dry. Results indicate an increase in rut depth with the removal of anti-strip additive from the mix, indicating the effectiveness of the additive in preventing moisture damage.

Finally the specimens were tested in the Superpave Shear Test Machine. Frequency Sweep and Repeated Shear tests were performed for each mixture with half of the samples again conditioned. The Frequency Sweep test measures the shear modulus and phase angle over a number of frequencies. The results of this test showed that the average shear modulus declined with moisture conditioning for each mix. The Repeated Shear test subjects the specimen to repeated loading and measures the accumulated plastic strain over a number of cycles, which can be used to determine rutting resistance. The results of this test corresponded with the Asphalt Pavement Analyzer results, with the rutting resistance decreasing with the removal of anti-strip additive.

Based on these results, it was concluded that a large concentration of baghouse fines can increase moisture sensitivity in asphalt pavement. It was also determined that the LOF 6500 anti-strip additive, in the 0.5 percent concentration, was sufficient to prevent moisture damage in mixtures with high concentrations of baghouse fines. Finally, the results showed an increase in stiffness related to increased baghouse fine content.