Comparative study of limestone calcined clay cement produced with mechanically activated kaolin and calcined kaolin

Limestone calcined clay cement (LC³) is a promising solution for mitigating CO₂ emissions in cement production by substantially replacing clinker with widely available supplementary cementitious materials. While calcination is the conventional method for activating clay, there is a growing interest in mechanical activation. Incorporating mechanically activated kaolin into LC³ formulation would offer a novel approach to producing this cement. This study aims to assess the impact of replacing calcined clay (CC) with mechanically activated clay (MC) in LC³ properties and relevant features. Accordingly, LC³ with MC substitutions ranging from 0 to 100 wt% were formulated. The resulting cements were characterised to evaluate their physicochemical properties, microstructure, strength, and pore distribution. LC³ incorporating MC exhibited comparable crystalline and amorphous phases to LC³ containing CC. However, the incorporation of MC accelerated hydration, leading to the earlier formation of carboaluminates and consumption of portlandite, alongside enhanced compressive strength at early curing stages. At 28 days, LC³ with 100 wt% of MC displayed similar compressive strength (42 MPa) to LC³ with 100 wt% of CC (40 MPa) with comparable pore distribution and microstructure. These findings validate MC's potential to substitute CC in LC³, offering an alternative for activating clay.