Optimization of Mechanical Properties and Durability of Steel Fiber-Reinforced Concrete by Nano CaCO3 and Nano TiC to Improve Material Sustainability

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To meet the growing demand for sustainable building materials in modern construction projects, nanomaterials are widely used in concrete to improve its mechanical properties, durability, and environmental adaptability. The effects of different calcium carbonate nanoparticles (NC) and titanium carbide nanoparticles (NT) substitution rates (0%, 0.5%, 1% and 1.5%) on the mechanical and durability properties of steel fiber-reinforced concrete (SFRC) were analyzed by experimental studies. We also analyzed the evolution of the microstructure, chemical composition, and the evolution of functional groups of concrete by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The results demonstrated that NC replacement of 0.5% and NT replacement of 1% was the optimal combination for the preparation of composite concrete. Compared to SFRC with 0% substitution for both NC and NT (CG), the 28-day compressive strength of NC0.5NT1 increased by 35.5%, the flexural strength increased by 26.5%, and the splitting tensile strength increased by 16.3%. The durability performance of SFRC has been significantly improved. After 150 freeze–thaw cycles, the quality loss rate of SFRC cured for 28 days decreased by 40.6%, and the relative dynamic elastic modulus increased by 7.7%. Microscopic analysis indicates that an appropriate amount of NC and NT replacing cement improves the hydration reaction process of SFRC, increases the content of chemically more stable C-S-H gel, but does not change the types of hydration products of the cement. NC and NT have a filling effect, improving the pore structure of concrete, which helps enhance the mechanical and durability performance of concrete. The results of the study provide a theoretical basis for the application of NC and NT as reinforcing particles for cementitious materials in sustainable building materials.