Calcined clay as a low-carbon cementitious material: Comprehensive review of treatment method, properties, and performance in concrete

The growing demand for sustainable construction materials has driven interest in calcined clay (CC) as a viable alternative to conventional cement and traditional supplementary cementitious materials (SCMs) like slag and fly ash. Calcination temperatures of 700–900℃ were commonly used to produce CC, with optimal performance observed at 800–850℃. The pozzolanic reaction of CC and its synergistic reactions with limestone form additional hydration products (calcium aluminosilicate hydrate (C-A-S-H) and carboaluminates phases) that enhance the mechanical and durability performance of concrete. Research indicated that utilization of CC can improve strength performance by 15–20 % compared to conventional concrete. However, the incorporation of more than 30 % CC in concrete may adversely affect the workability, strength, and durability performance. The use of clay with kaolinite content of 40–70 % is recommended for optimal resistance to chemical attack such as chloride penetration and carbonation. Workability reduction was observed due to high specific surface area and plate-like particle morphology of CC, causing increased water or superplasticizer demand at higher replacement levels to achieve the desired workability. Future research should focus on developing effective chemical admixtures to address the high absorptivity of CC and exploring the feasibility of using low-grade or locally available clays to produce calcined clay cement.