Review of natural mineral fillers for enhancing durability and performance mechanisms in cold mix asphalt for pavement maintenance

Cold mix asphalt (CMA) offers a lower-temperature pathway for pavement construction and maintenance, but its broader engineering application remains constrained by slow strength development, moisture susceptibility and variable resistance to deformation. Natural mineral fillers can mitigate these limitations through particle packing, binder-aggregate interactions and physicochemical reactions, yet the available evidence remains fragmented across conventional CMA, cold bitumen emulsion mixtures (CBEM) and related cold asphalt systems. This systematic review critically synthesises a 100-study evidence base published between 2020 and 2025 to establish how filler characteristics and interaction mechanisms govern the engineering performance, durability and sustainability of cold asphalt mixtures. Following the PRISMA 2020 framework, evidence on hydrated lime, limestone powder, silica-rich materials, volcanic ash, clay-based minerals and other mineral fillers was systematically screened, quality-appraised and synthesised. Direct evidence from CMA and closely related CBEM systems was distinguished from cold-recycled and other asphalt-material studies, which were used primarily for mechanistic and contextual interpretation. Across the evidence base, filler effectiveness was governed less by material identity alone than by mineralogy, particle size and morphology, surface chemistry, reactivity, dosage, emulsion compatibility and curing conditions. Performance improvements were associated principally with matrix densification, enhanced filler-binder-aggregate adhesion and, for reactive fillers, physicochemical and microstructural development during curing. Hydrated lime showed the most consistent evidence for improved moisture resistance, whereas silica-rich, limestone and other mineral fillers exhibited performance benefits that were more dependent on mixture composition and conditioning. The evidence does not support a universally superior filler or a single transferable optimum dosage across CMA systems. Instead, filler selection should be performance-based and matched to the dominant pavement distress, material compatibility, environmental exposure and locally available resources. The review establishes a mechanism-informed framework linking filler properties, mixture interactions and engineering response, while identifying standardised material characterisation, comparable performance testing and field validation as priorities for translating laboratory evidence into durable and resource-efficient cold asphalt pavement applications.