Enhancing Mechanical and Durability Properties of Polyvinyl Alcohol Fiber-reinforced Cement Composites with Fly Ash and Metakaolin: The Compensating Role of Metakaolin under Insufficient Curing

• 15% MK offsets performance loss from shortened 7-day curing. • 15% MK mix reached 68.6 MPa 28-day compressive strength under wet curing. • Adding 15% MK increased specific electrical resistivity to 58.5 kΩ·cm. • The optimized FRCC mix with 15% MK reduced water absorption to 4.9%. • Nonlinear models predict synergistic effects of MK and curing duration. Sustainable construction with high-volume fly ash (FA) composites is often hindered by slow pozzolanic kinetics, making the material performance highly vulnerable to premature curing termination. While a 7-day wet curing period is a common industrial limit, it is scientifically insufficient for the full microstructural development of FA-rich systems. This study investigates the mechanical properties and durability of Polyvinyl Alcohol (PVA) fiber-reinforced cement composites (FRCC) containing FA and metakaolin (MK) under various curing regimes. Four mix designs (0%, 5%, 10%, and 15% MK replacement) were evaluated under 7-day, 14-day, and fully wet curing conditions. Results indicate that under ideal curing, the 15% MK mix achieved superior performance with a compressive strength of 68.6 MPa and a specific electrical resistivity of 58.5 kΩ·cm. Crucially, reducing the wet curing duration to 7 days caused a sharp decline in the performance of the control (non-MK) mixtures. However, this deficit was effectively neutralized by MK incorporation, with the 15% MK replacement providing a 'compensation effect' that resulted in superior performance even under constrained curing environments compared to non-MK composites under ideal conditions. This research establishes MK as a potent early-age accelerator and a strategic tool for ensuring composite integrity in rapid construction. Finally, nonlinear regression models were developed to provide predictive design tools for field applications.