Durability Challenges of Low-Grade Calcined Clay Opposed to High-Volume Fly Ash in General Purpose Concrete

With the decrease in availability of common supplementary cementitious materials (SCMs) such as fly ash in Europe, the search for appropriate SCMs should be dealt with locally. A com-bination of abundant low-grade calcined clay and limestone powder has proven relatively in-expensive to produce while maintaining satisfying performance compared to existing cements. In this study, ternary cement mixtures containing 45 % ordinary portland cement and 55 % SCMs -limestone powder with either low-grade calcined clay or high-volume fly ash (HVFA), were compared in terms of freeze-thaw resistance, water permeability, carbonation, and compressive strength of concrete according to European standards. The main aim of the study was the evaluation of potential durability challenges of local limestone and calcined clay (LC3) binder and the possibility of its utilization as an ecological alternative to HVFA blends fitted for general application. The results suggest a similar performance of both binders in terms of compressive strength, carbonation, and freezing and thawing resistance, though the water penetration resistance seems to increase with the LC3 binder. The reduced water-permeable porosity of this binder, measured by mercury porosimetry, could influence the diffusivity of concrete, especially after carbonation.