Geopolymer as well cement and the variation of its mechanical behavior with curing temperature

Anthropogenic emissions of greenhouse gases are a major problem for all nations, and carbon dioxide (CO2) sequestration is one of the best practical solutions to reduce greenhouse gases. A large amount of CO2 is injected through sequestration wells into injection reservoirs. The injection wells play an important role; well integrity is an important part of any CO2 sequestration projects and well cement is the key to maintaining well integrity. To date, Ordinary Portland cement (OPC)-based well cement has been used and there are many problems associated with this, including cement degradation, durability issues, and sustenance in acid-rich environments. Therefore, this paper aims to study geopolymer as a well cement and the variation of its mechanical properties with different curing temperatures. Temperatures from ambient level (23 °C) up to 80 °C were considered, as well cement undergoes a range of temperatures from the ground surface to deep underground with a geothermal gradient of 30 °C/km. Stress-strain variations and crack propagation stress thresholds were studied using stress-strain and acoustic emission (AE) methods, and failure strain and orientation were studied using ARAMIS photogrammetry software for samples cured at different curing temperatures. The results show that the optimal curing temperature for higher strength is 60 °C; Young's modulus and Poisson's ratio generally increase with curing temperature. In general, crack closure, crack initiation, and crack damage thresholds increase with curing temperature. ARAMIS image capture showed that failure modes of low-temperature cured samples are diagonal, whereas elevated-temperature cured samples start to fail at the top and bottom compression plates. In addition, low-temperature cured samples exhibit higher strain (6–8%) at failure, while elevated-temperature cured samples exhibit low strain (0.8–3.5%) at failure