Differential Thermal Contraction of Asphalt Components

Abstract

Large differences between the coefficient of thermal contraction of mineral aggregate and binder has been associated with localised damage at the aggregate-binder interface at low temperatures. In this work, the coefficients of thermal contraction of different binders, aggregates and asphalt mixtures have been determined. Binder specimens were first produced by pouring hot bitumen into 200 x 50 x 50 mm³ moulds. The specimens were conditioned at various temperatures ranging from 10 to -20 ⁰C. The change in length was then measured to determine thermal strains as a result of cooling. It was found that linear coefficients of thermal contraction varied between 115 and 175 x 10^− 6 mm/mm/⁰C depending on grade and type of binder. Coefficient of thermal contraction of different aggregates was also determined. Rock specimens of the same dimension as the binder specimens were cut from large rock cores. The specimens were then conditioned at different temperatures and their change in length was measured. Three types of rocks namely limestone, granite and greywacke typically used in asphalt mixtures were employed. It was found that CTC of the aggregates varied between 7 and 10 x 10^− 6 mm/mm/⁰C, thus, 10 to 25 times lower than those of the binders. The coefficient of thermal contraction of various asphalt mixtures was determined using a volumetric and a composite model. Furthermore, predicted values were compared with those determined experimentally using beam shaped asphalt specimens cut from roller compacted slabs manufactured in the laboratory.