Study on alkylsilane-incorporated cement composites: Hydration mechanism and mechanical properties effects

Abstract Three silanes with different alkyl chain lengths were incorporated into PII 52.5 ordinary Portland cement to investigate their effects on cement hydration and mechanical development. The micro-mechanism of hydration process and hydrated products were well studied using Calorimeter, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Thermal gravimetric-Differential scanning calorimetry (TG-DSC). Results demonstrated that different alkylsilanes had diverse effects on cement hydration. In general, the shorter the alkyl chain length, the stronger the retardation. Furthermore, the porosity change due to the silane incorporated could be another reason for the decrease of the mechanical properties. Additionally, SEM images show that there are some fiber-like needle products formed on the surface of hydrated cement substrate. According to EDS analysis, they are likely composed of 2,4,4-trimethyl pentyl triethoxysilane (S1) and n-dodecyl triethoxysilane (S3), which might be produced from the reaction between calcium hydroxide and silane. In terms of water absorption reduction, S1 shows the lowest water uptake, which benefits from the branched structure in alkyl group of S1.