Calcined Marl and Clays as Alternative Materials for Cement Substitution

Abstract Transitioning to more sustainable materials than cement is vital for reducing the carbon emissions and ecological footprint associated with cement production. Ternary cement blends, particularly Limestone Calcined Clay Cements (LC3), are gaining attention as sustainable alternatives to Ordinary Portland Cement to reduce clinker content. Three clay samples from the western area of Chania, Crete, Greece, were calcined at 700 °C and reacted with saturated lime to assess their pozzolanic activity as potential cement substitutes. Additionally, a local marl was calcined at 800 °C and then hydrated to evaluate its binding capacity for designing mortars with hydraulic binders. The silica and alumina minerals in the calcined clays and marl, after reacting with lime and undergoing hydration, produced respectively calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H), which contribute to the hardening of plasters and mortars. The study includes Attenuated Total Reflection (ATR-IR) analysis, compression tests on mortar samples aged 1 to 4 months, and workability tests on fresh mortars. The results found that calcined clays, particularly metakaolin-rich samples, reacted more significantly with lime compared to those with high calcite content and low kaolinite. Mortars containing clays and lime required a similar water-to-binder ratio to achieve workability comparable to cement-based mortars. Compressive strength showed that the portlandite produced from the hydration of the marl was insufficient to fully react with calcined clay and cement to form C-S-H. This paves the way for ongoing studies to identify the minimum and optimal lime content required to effectively promote the hydrolysis reaction forming C-S-H, in accordance with LC3 principles.