Influence of viscosity modifiers on processing temperatures of recycled asphalt mixtures

Abstract

The production process of asphalt mixtures is high energy intensive and the cost of road construction material continues to increase annually. The cost of asphalt mixture production per m³ in Uganda is increasing at a rate of 8.0% per annum (UNRA, 2018). Most road agencies limit recycling to not less than 25% of RAP in asphalt concrete mixtures because of its inferior physical properties. However, waste RAP material continues to increase and pollute the environment. Sasobit additive was used in this study to investigate the feasibility of reducing the processing temperatures and also increase RAP content in Recycled Asphalt Mixtures (RAM). The objectives of the study were; to characterize RAM components against specification requirements, to evaluate the influence of Sasobit additive on rheological properties of virgin asphalt binder, and to assess the mechanical properties of Sasobit RAM prepared at warm processing temperatures. The control mixture consisted of virgin aggregates and asphalt 60/70 prepared at 160°C and 130°C mixing and compaction temperatures, respectively. Sasobit dosages used for all mixtures included 0, 1.5, 2.0 and 3.0%. Sasobit RAMs were prepared at 140°C and 120°C mixing and compaction temperatures, respectively. Sasobit modified RAM with RAP content of 0, 10, and 20% were prepared with asphalt 60/70 while RAP content of 30 and 40% Sasobit were prepared with asphalt 80/100. The physical properties of virgin aggregates, virgin asphalt and RAP material satisfied the general specifications. The rheological properties of Sasobit Modified Asphalt (SMA) showed that Sasobit reduces asphalt viscosity at temperatures above 110°C, attaining viscosity of 0.2Pa.s at 135°C with 4.0% Sasobit dosage. Sasobit additive lowered the conventional production temperatures of asphalt mixtures by 20°C resulting into 140°C and 120°C mixing and compaction temperatures, respectively. Sasobit dosages of 2.0% improved Stability and flow above the mean specification value for all RAP contents. The Indirect Tensile Strength improved above the minimum specification limit of 800kPa tested at 25°C for all RAP contents irrespective of the Sasobit dosage. The Tensile Strength Ratio improved for all RAP contents. Sasobit seems not to have influence ITS and TRS properties. Sasobit dosage of 2.0% is optimum to lower the production temperatures of RAM and 40% is maximum limit of RAP content usable in RAM. Detailed investigation of a possible chemical reaction that occurs between asphalt binders and Sasobit calls for further research.