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The impact of nanosilica on the properties and microstructure of cement-based products has lately attracted a lot of attention. The effects of colloidal nanosilica (CNS) at different concentrations on the hydration process and performance of cement-based composites reinforced with coconut coir were examined in this study. CNS was applied at concentrations of 0%, 2%, 4%, and 6% by weight of cement, respectively. The samples were evaluated in terms of flexural test, scanning electron microscopy (SEM), thermogravimetric analysis (TG-DTG), and X-ray Diffraction (XRD) after 7, 28, and 60 days of curing. Flexural strength improved by 13%, 11%, and 23% in the presence of CNS after 7, 28, and 60 days of hydration, respectively, as compared to the samples without CNS addition. The highest flexural strength was reported in samples containing 4% CNS. Beyond this, flexural strength decreases noticeably owing to the presence of too much nanosilica, which repressed the hydration process. The predominant causes of sample failure appear to be fiber breakage and fiber pull-out. In the sample containing 4% CNS, a dense structure was seen. The fibers had a strong bond with the matrix, showing that fiber/matrix bonding was improved. CNS served as a pozzolanic reaction promoter, converting CH to C-S-H, and a filler to improve cement microstructure. The CH content decreased when CNS was added, while the C-S-H gels increased.

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