title: Development of a New High Performance Cold Mix Asphalt
Creators: name: Herez, M
Publisher: name: Liverpool John Moores University
Year: 2021

description: In recent years, global climate change and energy shortages have become serious issues of common concern internationally. The majority of roads and highways are paved using hot mix asphalt (HMA) technology. The manufacture of hot mix asphalt is a key source of energy consumption, greenhouse gas emissions and air pollution. As such, efforts have been made to develop sustainable techniques to reduce energy consumption by lowering manufacturing temperatures, which in turn, will reduce CO2 emissions and subsequent negative impacts on the environment. Cold bitumen emulsion mixtures (CBEMs) are an excellent alternative to traditional HMA, from both an economic and environmental point of views. However, there are certain issues related to the mechanical properties of CBEMs that make them inferior to HMA, limiting their use to low traffic roads, reinstatement works and footways. Accordingly, the development of a CBEM with high early strength and minimal curing time is of increasing interest to researchers in the asphalt industry. The aim of this research work was to develop a new, high performance and environmentally friendly, surface course, cold bitumen emulsion mixture for heavily trafficked roads. This aim has been achieved by i) addressing the longstanding problems associated with conventional bitumen emulsions, namely large and non-uniform distribution of bitumen droplets within the emulsion, and ii) reducing the long curing time of CBEMs by replacing conventional limestone filler (LF) with a new secondary cementitious filler made primarily from waste materials. Ultrasound technology was used to reduce the size of the bitumen droplets through the cavitation phenomenon. A cationic bitumen emulsion (C50B4) was treated using ultrasound apparatus, over different periods of time. The results revealed an 85% reduction in mean droplet size (D50), under 7 minutes sonication treatment compared to the untreated sample. Reductions in D90 and D10 were 90% and 86%, respectively, in comparison to the untreated sample. The particle size distribution (PSD) curve shows more uniformly distributed droplets closer to the mean values, in comparison to the untreated emulsion. The viscosity of the 7minute sonicated bitumen emulsion decreased by 28%, compared to the untreated emulsion. CBEM-LF, made with 7-minute sonicated bitumen emulsion, showed an enhancement in indirect tensile stiffness modulus (ITSM) at 3 days curing by approximately 70%, compared with the same mixture containing conventional bitumen emulsion. To eliminate the long curing time required by CBEMs, a new cementitious filler was developed from waste materials and used as a substitute to conventional LF. The new alkali ternary blended filler, ATBF2, comprises ordinary Portland cement (OPC), a high volume of waste sewage sludge fly ash (SSFA) and calcium carbide residue (CCR). A waste calcium hydroxide solution was used as a replacement for the aggregate pre-wetting water in the CBEM. CCR played a vital role activating the SSFA by breaking the glassy phases of the non-amorphous silica in the SSFA, while the waste calcium hydroxide solution increased the hydraulic reactivity of the cementitious components. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used to investigate the development of hydration products in the new CBEM. Concentrations of heavy metals in the samples incorporating ATBF2, were observed to be less than the regulatory levels determined for hazardous materials. The mechanical properties of the novel CBEM incorporating both the sonicated bitumen emulsion and ATBF2 filler, were investigated in terms of ITSM at different curing times, rutting resistance, fatigue resistance, water damage resistance and age hardening. The said mixture offers a substantial improvement in stiffness modulus, compared to HMA and CBEM containing conventional emulsion and LF. The ITSM for the newly developed CBEM at 3 days of age, increased by approximately 19 times that of the conventional cold mixture, and almost 2.5 times that of traditional 100/150 HMA. The new mixture also displayed considerably higher resistance to permanent deformation in comparison to the reference cold and hot asphalt mixtures, demonstrating its potential for use in heavily trafficked roads. Resistance to fatigue was significantly enhanced by the use of both ATBF2 and the modified emulsion in the CBEM, compared to conventional cold and hot mixtures. This mixture is more durable because of improvements in resistance to water damage and enhanced long term ageing performance. This improvement has been achieved by the presence of smaller bitumen droplets that provide more bitumen surface area and even coating of aggregate particles. This helps form a cohesive mixture working in parallel with the hydration products which resulted from the hydration process of the cementitious filler in the presence of water within the bitumen-water solution.