Abstract
Concrete poured as linings of geothermal tunnel would deviate normal curing condition. A multiscale model based on continuum micromechanics, accounting for temperature-dependent factors, is established from the cement paste level to the concrete level. This model predicts the physical properties and compressive strength of concrete and is validated against measured strength, which incorporates the impact of high-temperature curing on the hydration degree, density of C-S-H, and chemical shrinkage of cement. Evolutions of the average hydration degree and compressive strength of concrete were experimentally investigated to this end, and then simulated with multiscale approach. The specimens were subjected to curing temperature 20°C, 40°C, 60°C, and 80°C for first 7 days while maintaining constant relative humidity of 100 %, and then water curing at 20°C for the rest days till tests. The high-temperature curing accelerates the hydration process, but the variance in hydration degree between standard temperature (20°C) and high-temperature conditions diminishes with prolonged water curing. An enhancement in compressive strength is also observed in the early stages of high-temperature curing, succeeded by a decline compared with standard curing after the 50th curing day. Quantitative analysis reveals that volume fractions of hydrates and porosity subjected to high-temperature curing show a substantial increase in the first 7 curing days, and the denser layer of hydration products formed on cement slows down the hydration in later curing ages. The complex evolution of strength in concrete undergoing high-temperature curing is influenced by temporal consideration (the hydration degree) and spatial considerations (the density of C-S-H and the chemical shrinkage of cement). The surge in hydration significantly contributes to strength promotion in early stages. However, the pivotal factor leading to strength deterioration is the increase of porosity when the difference in the hydration degree is less than 0.065.
Published Version
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