Activated clay and nanomaterial incorporated cement composite blends: A comprehensive review on reaction mechanism and performance

Cement production has become a significant contributor to global CO 2 emissions, underscoring the urgent need for sustainable cementitious alternatives. Among these, activated clays, notably metakaolin (MK), together with other calcined clays (CC), have emerged as promising Supplementary Cementitious Materials (SCMs) due to their high pozzolanic reactivity and environmental benefits. However, binary systems with either CC/MK or nanomaterials (NMs) often face intrinsic limitations, such as the inability of MK/CC to refine nanopores and the tendency of NM to agglomerate at higher dosages, thereby compromising mechanical integrity. This review evaluates the reaction mechanisms and performance characteristics of ternary CC/MK–NM cement composites. The review reveals that the ternary system exhibits a distinct micro–nano synergy, wherein NM accelerates early-age hydration via nucleation effects, while MK/CC sustain long-term pozzolanic reactions. CC-NM blended concrete composites have demonstrated the potential for peak relative strength increments of up to 65% achieved under optimized conditions, alongside marked enhancements in durability. Despite these advancements, challenges such as increased superplasticizer demand, difficulties in dispersion, and dosage optimization remain critical to ensure consistent performance. In summary, this paper provides an overview of current CC/MK–NM cement composite research, offering mechanistic insights and directs research toward the design of sustainable, high-performance cementitious materials for future application in construction.