Geological sequestration of carbon dioxide (CO2) has been found to be one of the best solutions to reduce greenhouse gases in the environment. The injection wells and well cement play a vital role in maintaining well integrity for successful sequestration projects. The use of ordinary Portland cement (OPC)-based well cement in underground wells has many disadvantages, including cement degradation, chemical attacks, durability issues and leakage. One of the best replacements for OPC- based well cement would be the use of geopolymer cement, as it is economical in production, sustainable in reducing waste products, consumes less energy, does not undergo chemical attacks, is durable, is resistive in acidic environments and possesses higher strength compared to OPC. Typical well cement will be exposed to different curing mediums such as ground water, brine reservoirs, carbon dioxide and other acidic mediums in down-hole environments. Therefore, this experimental work aims to study the mechanical behaviour of geopolymer saturated under low (5% NaCl) and high (15% NaCl) brine concentrations. Mechanical properties such as compressive strength, crack propagation stress thresholds and failure strain behaviour were studied for the samples saturated in brine for 14, 30, 60 and 90 days. It was observed that the compressive strength of geopolymer decreases under brine, and the reduction rate is less in 15% NaCl brine compared to 5% NaCl brine solution. Moreover, the crack propagation stress thresholds of geopolymer were higher in 15% NaCl brine compared to 5% NaCl brine. In addition, ARAMIS photogrammetric results of strain measurement revealed that the failure strain of geopolymer reduces with the introduction of brine.

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