Characterisation of Cold Asphalt Mixtures with the Addition of Active Fillers

Climate change, the limited availability of natural resources, and energy crises are putting pressure on the global societies? to employ low-energy and low-emission technologies for road pavement construction. Cold Recycled Materials (CRM) is an efficient and low-impact solution. CRM with Bituminous Emulsion (CRM-BE) is one of the most common types of CRM. CRM-BEs are created at ambient temperature by combining a high amount of Reclaimed Asphalt (RA) with Bitumen Emulsion (BE). BE used in CRM is typically composed of 60% bitumen and 40% water. Due to the presence of water in its composition, the mechanical properties of CRM-BEs are highly dependent on curing time and the remaining moisture in their structure. The presence of moisture in this mixture is an impairment to its complete consideration by paving authorities. Based on that, experiments concentrating on improving their early mechanical performance by adding active fillers into their systems, such as cement, were conducted. In the literature, the emphasis was mainly on obtaining higher strength and stiffness. However, doubts remain concerning issues that influence not only strength and stiffness but also cracking sensitivity. Adapting active fillers in CRM-BEs could make them behave like concrete. Therefore, they may show brittle behaviour and inherit shrinkage characteristics. Eventually, this results in CRM-BEs being sensitive to fatigue and fracture cracking under high strain load cycles. The inherent complications of incorporating active filler into CRM-BE should be kept under control as much as possible during mix design. Because of this, it would be regarded as a major advancement in CRM-BE research to produce a material with high early strength and short time delay requirements before structural loading without risking other performance features. Within the present study, the effect of using different active by-product fillers on the performance of CRM-BE was evaluated. The idea of the research is to provide a sustainable filler from waste material to be used as a filler to provide higher early mechanical properties without altering other performance aspects. To achieve this aim, four active fillers as well as cement as a reference filler have been used, which were: Ladle slag (LD) that has high CaO and Al₂O₃ content; Silica Fume (SF), with high silica content; and Ettringite binder (ET) that has the main components of Calcium Sulphoaluminate (CSA) cement made up from ladle slag and commercial gypsum. The fourth filler is a blended filler comprised of SF, ladle slag, and hard coal Fly Ash (FA). These fillers were used instead of Ordinary Portland cement (OPC). The results showed that, among the investigated fillers, the ET filler has a positive impact and can be used instead of conventional cement. Such advantages include improving the rheological properties and fatigue resistance of bitumen emulsion mastic while controlling drying shrinkage, increasing flexibility, improving the adhesion performance, offering a reasonable fatigue life with smoother fatigue line reduction, and reducing curing time with comparable long term mechanical performance.