Characterization and modeling the flow behavior and compression strength of the cement paste modified with silica nano-size at different temperature conditions

Abstract

In this study, the effect of nano-silica (NS) as an additive to the Ordinary Portland Cement was evaluated and quantified. Scanning Electronic Microscope (SEM), X-ray diffraction (XRD), Thermogravimetric Analysis (TGA), Fourier-Transform Infrared Spectroscopy (FTIR), and Raman Spectroscopy analysis were used to identify the cement and NS content. Experimental tests and modeling were conducted to quantify and predict the rheological properties of the modified cement in the liquid phase such as yield stress, maximum shear strength, plastic viscosity, and mechanical properties such as compressive strength of cement after hardening. The cement modified with NS was tested at water-to-cement ratios (w/c) of 0.35 and 0.45 and temperatures ranging from 25 °C to 75 °C. Non-linear regression (NLR) based model was used to evaluate the effect of nano-silica on the rheological properties and compressive strength of cement. Modifying the cement with nano-silica substantially reduced the volume of Ca (OH)₂. TGA tests showed that the 1% nano-silica additive leads to a decrease in the total weight loss of the cement at 800 °C by 82% due to the de-carbonation of CaCO3 in the hydrated compound and due to interacting the NS with the cement. The addition of NS increased the ultimate shear stress (τmax) and the yield stress (τo) by 15% to 53% and 23% to 186% respectively based on the NS content, w/c, and temperature. An additional 1% of NS to the cement paste the compressive strength increased by 14%–66% based on the curing time, and w/c. The unprecedented conclusions can be drawn in this study, which is the effect of the nano-silica content, water-cement-ratio and temperature effect on the plastic viscosity, yield stress and shear stress limit in the fresh stage (slurry) of the cement paste and also, the impact of the nano-silica content, water-cement-ratio and curing time on the compressive strength in the hardened stages of the cement modified with nano-silica were modeled. The experimental and the modeling results illustrated that the SiO2 nanostructure, which was mixed with the cement paste was highly beneficial in improving the rheological properties of cement paste and compressive strength after hardening.