Increasing the metakaolin content of blended cements by cationic latex adsorption: Towards more sustainable concrete

Metakaolin (MK) is a promising supplementary cementitious material (SCM) for replacing Portland cement (PC) in concrete due to its wide availability and low carbon footprint. However, achieving high PC substitution levels with MK (≥ 30 wt%) remains a challenge, as elevated MK contents are known to adversely impact workability, hydration kinetics, and the final mechanical properties of concrete. In this study, we demonstrate that cationic latex nanoparticles adsorb strongly onto the surface of MK, resulting in deflocculated MK dispersions that can be incorporated into cement formulations at substitution rates as high as 60 wt% without loss of workability. Although MK is known to trap sulfate anions, MK coated with 1.3 wt% latex is found to be immune to this phenomenon. As a result, the hydration kinetics of formulations containing 60% MK closely match those of pure PC. Remarkably, compressive strengths of mortars with 50–60% MK were comparable to those of PC-based mortars, while formulations containing 30–40% MK exhibited strength increases of 20%. These findings show that cationic latex nanoparticles enable the formulation of high-MK-content cements (up to 60 wt%) with no detrimental effects on workability or hydration, and with improved mechanical performance.