Comparative Effects of the Pristine and Amino-Functionalized Metal–organic Frameworks on the Mechanical Properties and Microstructures of Cement Pastes

The present work investigated the effects of MIL-101(Fe) and its amino-functionalized counterpart NH2-MIL-101 (Fe) on the mechanical properties, hydration processes and microstructure of cement pastes. Results showed that the addition of 0.05 wt% of these two kinds of metal-organic frameworks (MOFs) enhanced the 28-day compressive strength of cement pastes by 39.32% and 30.27%, respectively. Meanwhile, X-ray diffraction revealed that two MOFs exhibited different stability behaviors in alkaline simulated cement pore solutions. In addition, the hydration heat experiments disclosed that prepared MOFs expedited the hydration process of the Blank group by about 1 h and increased the hydration degree. Mercury intrusion porosimetry results showed that the employed MOFs could refine pore size, increase gel porosity and optimize pore structure. Furthermore, the formation of Ca-BDC complexes in MIL-101(Fe)-doped cement composites promoted the hydration process and then enhanced the compressive strength. Also, the formation of Ca-BDC was further confirmed based on density functional theory calculations.