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Multiscale fiber hybridization is an essential method for enhancing and toughening cement-based materials. In this study, the influence of the content of calcium carbonate whiskers (CW) and polyvinyl alcohol (PVA) fibers on the flexural properties of cementitious composites containing 1.5% by volume steel fibers was investigated by using the hybridization of CW, PVA fibers, and steel fibers based on the four-point bending notched test. The distribution characteristics of PVA fibers and steel fibers in multiscale hybrid fiber-reinforced cementitious composites (MFRC) were analyzed and evaluated using backscattered electron imaging (BSE). The results demonstrated that the addition of an appropriate amount of CW and PVA fibers effectively improved the flexural performance of steel fiber–reinforced cementitious composites and promoted a more uniform distribution of steel fibers within the matrix. The MFRC with 1% by volume CW, 0.3% by volume PVA fiber, and 1.5% by volume steel fiber (C1P03S15) exhibited the highest flexural toughness coefficient (σb) and fiber dispersion coefficient (γ), which increased by 46.2% and 81.4%, respectively, compared to the control group without CW. Furthermore, a strong correlation between σb and γ was observed through fitting, indicating the potential for guiding practical engineering applications. [ABSTRACT FROM AUTHOR]

To meet the demands of the construction industry for cement-based materials, nanomaterials are frequently used as additives to enhance the mechanical properties and durability of cement-based materials. This study investigates the effects of UiO-66 and its amino-functionalized derivative UiO-66-NH2 on the mechanical properties, hydration process, and microstructure of cement-based pastes with a water-to-cement ratio of 0.4. The experimental results indicate that compared to the blank group (pure cement), the addition of 0.05% of these two metal-organic frameworks (MOFs) can increase the compressive strength of cement pastes by 13.2% and 21.8%, respectively, and the flexural strength by 21.2% and 25.5%, respectively, at 28 days. X-ray diffraction results demonstrate that UiO-66 and UiO-66-NH2 exhibit similar stability behavior in cement pore solutions. The incorporation of these two MOFs enhances hydration levels in the cement hydration process, fostering increased production of hydrated calcium silicate gel. Concurrently, it fine-tunes the cement's pore structure, amplifying its mechanical strength. This research confirms UiO-66 and UiO-66-NH2 as promising nanocement additives, laying a theoretical groundwork for incorporating UiO-66–type MOFs in composite materials based on cement. [ABSTRACT FROM AUTHOR]