The Combined Effect of Varying Proportion of Fines And Anti Stripping Agent on Asphalt Concrete Mixtures

Abstract

Moisture damage has been one of the major concerns for hot mix asphalt (HMA) pavements. In an asphalt mixture moisture damage can be defined as the loss of strength, durability and stiffness due to presence of moisture leading to adhesive failure at the binderaggregate interface and/or cohesive failure within the binder-filler mastic. In this research efforts were made to evaluate the moisture susceptibility of a dense-graded surface HMA mixture using simple performance test (SPT) and Superpave indirect tensile test (IDT). The nature and extent of fines (passing no 200 sieve) can have a major effect on the moisture damage potential of the hot mix. Coating of fines (dust) on the aggregate can prevent the asphalt binder from bonding directly to the surface of the aggregate. Therefore SPT and IDT tests have been performed by varying the proportion of fines from (3%, 6% and 9%) in the mix. For each proportion of fines optimum asphalt content has been determined and was used for further preparation of test specimens. The addition of hydrated lime [Ca(OH)2] to asphalt mixtures improved the adhesive bond between aggregate and bitumen, also reduces the occurrence of stripping. In addition when aggregates are coated with clays, hydrated lime react pozzolanically to remove those deleterious materials that would otherwise damage the mixture. Therefore hydrated lime has been used as antistripping agent in this research. The amount of antistripping agent incorporated was 1.5% by weight of dry aggregate. Pen Grade 60-70 bitumen and NHA class B aggregate gradation were evaluated in this study. Standard Marshall Mix design procedure was employed to design the asphalt mixtures. For all the tests cylindrical samples were compacted using Superpave Gyratory Compactor (SGC). A freeze-thaw cycle was given to condition the specimens according to ASTM D 4867. Laboratory test results and statistical analysis performed using Minitad-15 software suggests that hydrated lime is an effective antistripping additive and improves the stability of asphalt concrete mixtures.