Diverse effects of metal–organic frameworks on microstructure and compressive strength of cement-based composites

The modern construction industry is continuously demanding the reinforcement of the mechanical properties of cement-based materials. To realize the targets, intensive investigations have been conducted through the fabrication of micro-/nano-particles–cement composites during the past decades. The present work aims to exploit the metal–organic frameworks (MOFs)-doped cement-based materials that have been rarely reported, including MOF-5, HKUST-1, ZIF-8, UiO-66, and MIL-68(Al). Their decomposition behaviors in the simulated cement pore solutions are observed, and results demonstrate that ZIF-8, UiO-66, and MIL-68(Al) maintain structural integrity, while MOF-5 and HUKST-1 are destroyed. With the doping concentration of 0.1 wt%, MOF-5 and ZIF-8 result in significant improvement in the compressive strength of hardened pastes. The 28-day compressive strength of hardened pastes C-MOF-5 increases by 28.75%, and C-ZIF-8 by 24.65%, which benefits from the promoting effect for cement hydration, the optimization for the product structures, and the filling effect. HKUST-1 and UiO-66 improve the 3-day and 7-day compressive strength of cement-based composites, but the enhancement of the 28-day strength is not dramatic. By contrast, the compressive strength of 28-day MIL-68(Al)-doped cement-based materials (C-MIL-68(Al)) decreases because of the augmented porosity, the excessive Ca(OH) 2 crystals in the pores, and the generated calcium carbonate. These findings lay a foundation for the utilization of MOFs in cement-based composites. •MOFs affected the compressive strength of cement-based materials variously. •Distinct behaviors of MOFs in simulated cement pore solutions were disclosed. •Compressive strength of the composites were elucidated in terms of microstructures.