Improving the Stripping Resistance of Local Hot Mix Asphalt Containing Basalt Aggregate by the use of Cement

Abstract

One of the main reasons behind the appearance of early stripping and raveling in many roads in the Sana'a region is the use of basalt aggregate as the main component in both coarse and fine aggregate portions. Although this type of aggregate has an excellent behaviour in terms of compression strength, resistance to polishing/abrasion, resistance to weathering and chemical attack, it has, on the other hand, a low adhesion to asphalt due to its low porosity and absorption properties. This draw-back makes the
stripping potential of the asphalt concrete mixes high. The possibility of improving the properties of local asphalt concrete mixes, containing basalt aggregate, in term of stripping resistance is the focus of this paper. In this study, the normally used dust aggregate mineral filler, the material smaller than 0.075 mm, was replaced by Normal Portland Cement at different portions. The replacement includes four levels, namely 0%, 50%, 75% and 100%.
Results showed that replacement of dust aggregate mineral filler by cement not only increases the adhesion properties between asphalt and aggregate (stripping resistance) but also improves other properties of the asphalt concrete mixes such as stability and density. The optimal mix was the mix that
had coarse and fine basalt aggregate and 5%, by total of weight of the mixture, cement filler. The optimal mix showed superiority, over the tested mixes, in all the evaluated properties, which were Marshall Stability, indirect tensile strength and stripping resistance.
The study was expanded to evaluate/compare the local practice in evaluating stripping resistance (at air voids equal to that obtained from mix design i.e. close to 4%) with that presented in AASHTO T283-89 (at 7% air voids). Results showed a significant deviation between the two methods. The stripping resistance at 4% air voids was significantly higher than that at 7% air voids. Thus, and due to the incompatibility between the two methods, the local practice may provide misleading results by accepting mixes with apparently higher stripping resistances while the actual resistances, according to international standards, are not so. Therefore, a recommendation for not using local practice in evaluating stripping resistance was presented.