Evaluation of the different type of Sol-gel process with silane for steel microfibers surface modification on properties of ultra high-performance fiber-reinforced cementitious composite

<p dir="ltr">The primary mechanism of stress transfer between the fiber and the matrix is governed by the interface region between the fiber and the cementitious matrix, which is rich in calcium hydroxide (Ca(OH)₂). Calcium hydroxide is a byproduct with low mechanical strength and is intrinsic to the cement hydration process. Leveraging this characteristic, the deposition of silica-based materials on the fibers opens up potential for enhancing the interface region through reaction with Ca(OH)₂. In this context, the treatment of metallic fibers with Tetraethoxisilane (TEOS) presents potential for depositing silica on the fiber surface, this may react with this calcium hydroxide and could promote depositions of Calcium silicate hydrates in this region, densifying this interface. In this study, various types of dip-coating treatments of metallic fibers with TEOS were evaluated, using different silane concentrations (0.1 %, 1.0 %, and 10 %) and different alkaline treatments (sodium hydroxide (NaOH) and Ca(OH)₂), aiming to obtain a silica-rich film. Microstructural analyses of the fibers pre- and post-treatment, mass variation analysis of the fibers post-treatment, as well as tests on the fiber-reinforced composite, including workability, isothermal calorimetry, modulus of rupture (MOR), and compressive strength were conducted. The results showed that silane was deposited on the fiber surface, as indicated by Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), and there was an increase in fiber mass depending on the TEOS concentration in the functionalization solution. In the composite, greater workability was observed with higher TEOS concentrations, while no clear trend was observed in the calorimetry results, with variations of around 10 % in the induction period and silicates peak heat. In terms of MOR, the samples treated with TEOS showed strength values up to 15 % higher compared to the reference, while no significant increases were observed in compressive strength.</p>