Effect of calcined clay reactivity on the risk of restrained shrinkage‐induced early‐age concrete cracking

Abstract A combination of limestone and calcined clay has emerged as a promising supplementary cementitious material due to its abundant availability to replace traditional supplementary cementitious materials such as fly ash or ground‐granulated blast‐furnace slag in reducing concrete's carbon footprint. Although different properties have been considered, very limited attention was paid to the early‐age cracking behavior of limestone calcined clay cement (LC3) concretes. This study aims to investigate the influence of calcined clay reactivity on the early‐age cracking potential of LC3 concretes using the restrained ring test. Mechanical properties, time to cracking, tensile creep coefficient, and total shrinkage were measured. Results showed that the reactivity of calcined clay significantly impacted total shrinkage, creep coefficients, and time to cracking. LC3 concretes exhibited higher tensile creep coefficients than pure ordinary Portland cement concrete, which can provide beneficial tensile stress relaxation delaying concrete cracking. An apparent calcined clay reactivity coefficient ( R app ) was proposed correlating well with the time to cracking of the restrained LC3 concrete rings, thus offering practical guidance for the selection of suitable calcined clays and mix designs for specific high‐risk applications.