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

Abstract

The reduction of clinker content in cementitious materialsis considered one of the key strategiesfor 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 results obtained 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.