Effect of Zr-based metal–organic framework (MOF-808) on strength development of cement pastes and its phase transition on mechanisms of cement hydration

Nanostructured materials can regulate the performance of cement-based materials at the nanoscale and thus attract intense interest in the cement community. However, there are still few studies on modifiable and large specific surface area metal–organic frameworks (MOFs) to regulate cement properties, which are still in the preliminary exploration stage. In this work, the nanoporous Zr(IV)-based MOF-808-modified cement-based composites have been investigated, focusing on the effects of MOFs on various aspects of compressive strength and microstructure of hardened cement pastes as well as cement hydration, and so on. Results showed that MOF-808 can chemically adsorb Ca2+, Fe3+, and Al3+ released from cement, and the adsorption capacity of Ca2+ increased greatly when the crystalline MOF-808 was transformed into an amorphous state. With the MOF-808 dosage of 0.15 wt%, the compressive strength at 3, 7, and 28 d increased by 15.56%, 25.53%, and 13.03% in comparison with the Blank group, respectively. Additionally, MOF-808 delayed the hydration of cement, reduced the heat of hydration, and shortened the delay time, which was reduced when the dosage of MOF-808 was increased. The addition of MOF-808 promoted the generation of C-S-H gels, refined the pore structure within the hardened cement paste, and reduced the content of pores larger than 10 μm. Finally, the influence mechanism of MOF-808 on cement hydration and strength development was proposed.