Performance of warm mix asphalt containing coal bottom ash as alternative aggregate

Abstract

The increase in energy usage, material cost and environmental concerns encourage the need for cheaper and environmentally sustainable asphalt pavements. The development of Warm Mix Asphalt (WMA) technology has brought environmental and economic benefits. However, there are significant concerns related to WMA performance, such as rutting potential and moisture susceptibility. Recent research shows that the recycling of industrial by-products in WMA mixture offers technical benefits for road construction. Therefore, this research aimed to evaluate the compatibility of Bottom Ash (BA) as fine aggregate in WMA production using chemical additives. The research was initiated with the physicochemical and mineralogical characterisation of BA compared to the granite aggregate. Laboratory tests were conducted to investigate the behaviour of binder incorporated with chemical additives (Cecabase RT and Evotherm 3G) at concentrations of 0.3%, 0.4% and 0.5% by the total weight of 60/70 penetration grade bitumen. The compatibility of the additives, optimal dose, and production temperature for WMA was evaluated and compared to the control asphalt mixtures through the mechanical properties. Laboratory tests were also carried out to assess the performance of the asphalt mixtures, including moisture susceptibility, resilient modulus, dynamic creep, rutting resistance, and cooling rate. The mixtures’ potential contamination of leachates and pollutant emissions were assessed using a TCLP test and a combustion analyser. The characterisation of BA disclosed that it is porous and rough-edged granular particles with high abrasion loss, which does not favour its use as coarse aggregates but is applicable as fine aggregate for producing asphalt mixtures. The Marshall properties of the mixture containing BA satisfied the minimum requirements for the design of the binder course. The addition of chemical additives did not significantly change the binder properties, and the viscosity remained un-change. BA improved the tensile strength, resilient modulus, and resistance to permanent deformation of WMA mixtures by increasing aggregate interlocking and stiffness. The incorporation of BA into asphalt also did not indicate the presence of heavy metals but slightly increased the carbon dioxide emission compared to the control asphalt. However, the reduction of 25°C in production temperature significantly reduced the concentration of pollutant emissions and energy usage. Evotherm 3G combined with BA and granite aggregate produced a productive WMA mixture by eliminating hydrated lime as an anti-stripping agent. In conclusion, the WMA mixture with bottom ash (BAWMA) demonstrates a stiffer and more durable mixture for the binder course.