Tailoring the performance of cementitious composites through zinc oxide–containing deep eutectic solvents

Abstract

The reduction of clinker content in cementitious materials is considered one of the key strategies for lowering CO2 emissions associated with cement production. However, low-clinker cements often exhibit reduced early-age performance and increased sensitivity to microstructural modification, creating a need for multifunctional admixtures capable of improving both technological and functional properties. This study investigates the effect of a choline chloride–urea deep eutectic solvent modified with ZnO (DES-ZnO) on low-clinker cement composites (CEM II/B-V, CEM II/A-LL, CEM V/A), including an assessment of their environmental performance. The evaluation encompassed workability, hydration kinetics, mechanical performance, microstructure, and antimicrobial activity. Incorporation of DES-ZnO improved workability in all analyzed systems, with the most pronounced effect observed for low-clinker cements. Flexural and compressive strength values increased throughout the curing period, reaching approximately 11–12 MPa and 55–65 MPa, respectively, after 56 days. SEM observations indicated a more homogeneous and continuous microstructure in the modified systems, while XRD analysis confirmed that the overall phase composition remained generally unchanged. Calorimetric measurements showed that the influence of DES-ZnO on hydration heat evolution was moderate and dependent on cement composition. Importantly, DES-ZnO imparted strong antimicrobial properties, substantially limiting microbial growth and, in some cases, achieving complete inhibition. From an environmental perspective, the addition of DES-ZnO resulted in only a minor increase in embodied carbon compared to the dominant contribution of cement. The obtained results demonstrate that DES-ZnO can act as a multifunctional admixture for low-clinker cement systems, improving mechanical performance, workability, and antimicrobial resistance without substantially altering the hydration mechanism.