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Performance of calcium sulfoaluminate cement-based mixtures used for permafrost regions
- Author / Creator
- HUANG, Guangping
Canada has approximately 50% of land mass covered with permafrost. With the increasing of mining and construction activities in permafrost regions, cement-based mixtures (e.g., concrete, shotcrete, backfill, and grout) are expected to be increasingly used in these regions. However, cold temperature (< 5 ºC) causes the slow strength development of cement-based mixtures, which is unfavorable since it decreases construction efficiency, increases costs, and raises safety issues. In addition, early-age frost damage may happen if cement-based mixtures could not gain sufficient strength (compressive strength 3.5 MPa) before getting frozen. Once early-age frost damage happens, the strength of cement-based mixtures cannot be ensured to reach an adequate value even if it is re-cured at normal temperatures (e.g., 20 °C), which is also unsafe.
In response these issues, this Ph.D. program aims to develop calcium sulfoaluminate (CSA) cement-based mixtures for permafrost region applications. Experiments were conducted to investigate the hydration reaction, strength development, resistance to early-age frost damage, and thermal properties (e.g., thermal conductivity, diffusivity, and heat capacity). A numerical model was developed to predict the temperature profiles in hardening CSA cement-based mixtures.
The results show that the hydration reaction and the strength development of CSA-based mortar were much faster than Portland cement-based mortar at cold temperatures (< 5 °C). For example, CSA cement-based mortar cured at -10 °C achieved a UCS of 15.5 MPa at 1 day, while OPC-based mortars almost have no strength developed at 28 days. CSA cement-based mixtures also showed high resistance to early-age frost damage owing to the fast strength development. After re-curing, CSA cement-based mortar that had exposed to -10 °C reached 117.8% of the UCS of the same mixtures directly cured at 23 °C, while the data for OPC-based mortars with and without antifreeze admixture (calcium nitrate) were 56.0% and 45.1%, respectively. In addition, the thermal conductivity of 28-day CSA cement-based mortars reduced from 0.97 W/m·K to 0.57 W/m·K, 0.29 W/m·K, and 0.13 W/m·K when 30%, 60%, and 100% volume of aggregates were replaced with expanded perlite. These CSA cement-based thermo-insulting mortars are expected to not only provide mechanical support, but also work as thermal insulation materials for mitigating the heat exchange among permafrost, cement-based mixtures, and air. At last, the developed numerical model was validated by comparing the modeled temperature profiles with experimentally measured temperature profiles in hardening CSA cement samples. After validation, the influence of curing temperature, curing modes (e.g., curing in permafrost or curing in cold air), and sample sizes on the temperature profiles of hardening CSA cement mixtures was investigated and compared with that on an OPC-based mixture. The results suggest that samples should be cured in cold soil or sand when investigating the performance of cement-based mixtures used in permafrost regions since the different curing modes caused a large influence on the temperature profiles of hardening cement-based mixtures. The temperature gradient in CSA-based sample was more significant than that in OPC-based sample. Precautions are needed to control the thermal cracks when CSA cement-based mixtures are used in cold temperatures, even if the structure size is small (e.g., Ø300×600mm).
Overall, this thesis developed CSA cement mixtures that can achieve fast strength development and have high resistance to early-age frost damage for permafrost region applications. The findings provide a new solution to accelerate strength development and prevent early-age frost damage when cement-based mixtures are applied in permafrost regions.
- Graduation date
- Fall 2021
- Type of Item
- Doctor of Philosophy
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.