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Topic

CO2 Sequestration in Concrete: Assessing Impacts on Microstructure, Plastic Properties, Mechanical Performance, and Long-Term Durability

Department of Civil Engineering

Date & location

• Friday, April 11, 2025
• 2:00 P.M.
• Engineering & Computer Science Building, Room 227

Examining Committee

Supervisory Committee

• Dr. Rishi Gupta, Department of Civil Engineering, University of Victoria (Supervisor)
• Dr. Thomas Froese, Department of Civil Engineering, UVic (Member)
• Dr. Rodney Herring, Department of Mechanical Engineering, UVic (Non-Unit Member)

External Examiner

• Dr. Dennis Hore, Department of Chemistry, University of Victoria

Chair of Oral Examination

• Dr. Kate Moran, School of Earth and Ocean Sciences, UVic

Abstract

The 20^th century has seen rampant industrialization, a boost in manufacturing, afforestation in urban areas and extensive extraction of natural resources and fossil fuels. With a sudden surge in demand for power, transportation and housing, anthropogenic CO₂ emissions are on the rise and have reached unprecedented levels which the earth never experienced for several decades. With 37.5 billion metric tons of CO₂ emissions released in the atmosphere in 2024, as compared to 4.8 billion metric tons released in 1940, global temperatures are rising aggressively. Additionally, the population across the world is growing exponentially. As a result, there has been significant demand for infrastructure and housing. The increase in demand for building materials has indirectly increased CO₂ emissions. Additionally, cement manufacturing alone is responsible for 7% of the global emission. Hence, all sectors, including the construction industry, are exploring for green and sustainable products and practices to counter global temperature rise.

Ongoing research has shown that adding CO₂ during the mixing or curing stage of concrete improves its mechanical properties. The purpose of this study was to determine whether adding CO₂ to concrete during the mixing process had any positive effects on microstructural, mechanical, and durability properties. The formation of calcium carbonate (CaCO₃) results in densification of the microstructure of concrete. Compressive strength tests showed an improvement of 10-20%, particularly in samples with 0.5% to 0.75% CO₂ dosage, which mainly attributed to CaCO₃ formation. Additionally, compared to control concrete, a 5-10% improvement in the flexural strength was observed in the CO₂-sequestered concrete samples. Thermal Pyrolysis tests confirmed a higher CaCO₃ content with CO₂ uptake of 2-3%. Additionally, the microscopy and infrared spectroscopy analysis indicated the presence of CaCO₃, thereby confirming the densification and the early carbonation process. Conversely, the concrete slump immediately decreased after CO₂ addition, mainly due to the additional mixing time and formation of carbonic acid and CaCO₃ with heat release. Although an additional dose of superplasticizer was used to increase slump in this experiment, balancing the dosage with optimum mixing time and a trade-off between increased strength and workability could be explored. This study has also developed a multi-linear regression model which concrete technologists can utilize to assess the compressive strength of concrete and use the same while designing mixes that employ CO₂.

This study also assessed the long-term effects of adding CO₂ during the mixing stage of concrete on its durability and long-term performance under accelerated conditions. Test results indicated that densification of the matrix enhanced its durability. Lower RCPT and permeability values and higher resistivity readings were observed for dosages between 0.5% and 1% in comparison with control concrete samples. An enhancement in the resistance of concrete to freeze-thaw (F-T) cycles was also observed for CO₂-sequestered concrete samples. CO₂ dosages between 0.5% and 0.75% showed improved performance to F-T cycles, as compared to control concrete, observed by lower mass loss, less surface scaling and increased stiffness. Concrete slab panels exposed to 50 alternating 24-hour wetting and drying cycles at 50–60°C with and without NaCl solution showed that CO₂ dosages ranging from 0.5% to 0.75% increased corrosion resistance in a chloride-free environment. CO₂-sequestered concrete indicated a corrosion rate that was approximately 30–35% lower than the control by 50 cycles for CO₂ dosages of 0.5% and 0.75% in the set that had a wetting cycle with potable water at 23 ± 2°C and a drying cycle at 50°C.

Corrosion rates also decreased by 25–30% for CO₂ dosages of 0.5% and 0.75% in the set with a wetting cycle with potable water at 23 ± 2°C and a drying cycle at 60°C in comparison to the control, suggesting improved durability. However, both control and CO₂-dosed concrete suffered extremely high corrosion rates under saline conditions in the set with a wetting cycle with potable water at 23 ± 2°C and 5% NaCl and a drying cycle at 60°C. This test shows that in chloride rich environments, only adding CO₂ to concrete without additional changes to the mix design and supplementary protection to steel will not help in resisting corrosion.

A Life Cycle Analysis (LCA) was conducted for CO₂-sequestered concrete with varying CO₂ dosages and the mix with 0.75% CO₂ dosage indicated better environmental performance through a 37% decrease in normalized global warming potential over the control mix. However, challenges pertaining to the high cost of capturing, storing and transporting CO₂ needs to be addressed for large-scale implementation in the construction industry.

In a nutshell, this study experimentally assesses the benefits of CO₂ addition on the microstructure, plastic and mechanical properties and long-term durability, thereby contributing to the development of a sustainable and green construction material. While challenges pertaining to the loss in workability, high cost of CO₂ and acceptance by industry remain, this technology presents a positive approach towards green and sustainable development.