Calcined low-grade Dutch clays as partial cement substitutes: pozzolanic performance and cost efficiency

Calcined low-grade Dutch clays offer a sustainable alternative as partial Portland cement replacements. This study demonstrates the practical valorization of low-grade 2:1 Dutch clays as partial Portland cement replacements, a departure from the conventional focus on high-kaolinite sources. Four clays (14.8–32.8 wt.% kaolinite) were assessed for their pozzolanic reactivity, mechanical performance, and economic viability. Mortars with 20 wt.% cement replacement achieved 28-day compressive strength up to 43.3 MPa, with one clay meeting ASTM C618 requirements. Pozzolanic reactivity correlated with kaolinite content, while higher replacement levels modestly reduced early strength. Economic analysis revealed that 20 wt.% replacement lowers production costs without compromising performance. These findings highlight a novel, cost-effective approach to integrate abundantly available low-grade clays into cementitious systems, providing a scalable strategy to reduce CO2 emissions and advance sustainable construction practices in regions with limited high-quality clay resources.