A Critical Review of Wollastonite as an Additive in Concrete: Mechanical and Durability Properties

Abstract

Wollastonite, a naturally occurring calcium metasilicate mineral with an acicular crystal habit, has attracted sustained attention as a partial replacement for cement and fine aggregate in concrete and related cementitious composites. Its fibrous morphology, moderate pozzolanic reactivity, and favourable filler effect distinguish it from conventional supplementary cementitious materials such as fly ash, ground granulated blast-furnace slag, and silica fume. This review critically synthesises the published literature on the influence of natural and synthetic wollastonite on the mechanical and durability performance of cement-based materials, spanning conventional concrete, mortar, self-compacting concrete, geopolymer systems, and ultra-high-performance concrete. The evidence indicates that wollastonite incorporation at 5 to 15 per cent cement or sand replacement levels generally improves compressive and flexural strength, reduces drying shrinkage and microcracking, and densifies the pore structure, leading to lower water absorption, reduced chloride ion penetration, and improved resistance to freeze–thaw and sulfate attack. These benefits are attributed to a combination of physical filler action, crack-bridging by acicular particles, and limited pozzolanic reaction with calcium hydroxide. At higher replacement levels, dilution of clinker content and increased water demand can offset these gains, producing an optimum dosage range rather than a monotonic improvement. The review also considers wollastonite's role in carbon dioxide mineralisation and its environmental profile relative to other mineral admixtures, identifies methodological inconsistencies across the literature concerning particle size, aspect ratio, and curing regime, and outlines priority directions for future research, including standardisation of testing protocols and long-term field validation.