Experimental study on the mechanical properties of cement-based grouting materials after exposed to high temperatures

This paper experimentally investigates the compressive and flexural strengths of cement-based grouting materials used in grouted sleeve connections at both room temperature and after exposure to high temperatures. The tests were conducted at three different temperatures (200°C, 400°C, and 600°C) using two cooling methods (natural-cooled and water-cooled), and various durations of constant temperature and dwell times after high-temperature exposure were considered. The mechanical properties of the grout after high temperature were comparatively analyzed, and the changes in the microstructure were observed and analyzed using a scanning electron microscope. The experimental results demonstrate a linear decrease in the dynamic elastic modulus as the temperature rises. Moreover, the sample tested at 200°C exhibits an upward trend in its mechanical properties due to the development of stable phases of calcium silicate hydrate (C-S-H) and the additional effects of secondary hydration. However, beyond 400°C, a substantial decomposition of C-S-H occurs, leading to severe internal structural damage and a sharp decline in mechanical performance.Furthermore, the cooling method employed also influences the mechanical properties of the grouting material after exposure to high temperatures. The sample cooled by water displays a slight increase (up to 10%) in the dynamic elastic modulus, attributed to the secondary hydration of surface hydration products, compared to the naturally cooled sample. Nevertheless, the water-cooled sample experiences an uneven temperature distribution caused by the temperature disparity between its interior and exterior, exacerbating internal damage. As a result, their flexural strength and compressive strength exhibited varying degrees of decline, up to 43.9% and 27.9%, respectively, compared to natural-cooled specimens. Microscopic observations revealed that exposure to high temperature induced significant physical and chemical changes in the cement-based grouting materials, which were closely correlated with their macro mechanical properties. Based on the experimental study, a calculation formula for the discount coefficient of flexural and compressive strengths of the cement-based grouting materials after exposure to high temperatures was established through data analysis. The computational results demonstrated good agreement with the experimental findings. Finally this study provides reliable and valuable test data for investigating the bonding properties between reinforcement and grouting materials in grouted sleeve connections