Strength characteristics of cement slurry in high geothermal tunnel environment

The early-age strength of grouting material is crucial for tunnel support under high geothermal temperatures. Grouting materials (such as the most commonly used cement slurry) hydrate and solidify under the condition of variable temperature curing after entering the real stratum. However, the development process of early strength of cement paste under the condition of variable temperature curing is still unclear. This study aims to elucidate the environmental effects of high ground heat tunnels on the early strength development of cement stone. The cement slurry undergoes variable temperature curing under three different temperatures (T=40℃, 60℃, 80℃) and two different relative humidity conditions (H=5%, 95%) through design experiments. Through the compressive strength test, combined with X-ray diffraction (XRD), scanning electron microscope (SEM) and nuclear magnetic resonance (NMR), the microscopic characteristics were studied. The results indicate that the strength of cement stone under variable temperature curing is lower than that under constant temperature curing at the same temperature. The influence of variable temperature curing conditions on the strength variation of samples with high W/C and age was greater at 80℃. The research results are helpful to understand the influence of environmental effects of high ground temperature tunnels on the properties of grouting materials.