Novel approach to microscopic characterization of cryo formation in air voids of concrete

Portland Cement Concrete (PCC) production is one of the major contributor to atmospheric Carbon Dioxide (CO₂) emission. Geopolymer Concrete (GPC) as an alternative construction material has the potential to reduce CO₂ emissions while creating durable structures. Freezing and thawing is an exemplary concrete deterioration mechanism that can cause widespread damage in concrete structures. Concrete structures exposed to freeze-thaw cycles delaminate due to expansive stresses induced when liquid converts to ice. There are numerous theoretical studies that have been done focused on capturing the effect of freeze-thaw cycles on microstructure of PCC. However, there is limited and no experimental work reported on cryo formation inside the air voids of PCC and GPC respectively. The main issue here is that most of the scanning electron microscopic devices cannot maintain the low temperature required to capture an image from a frozen sample. The amount of internal stress due to cryo formation and temperature range of cryo formation can be determined by investigation of morphology of the cryo products. Hence, in this study attempts have been made to investigate the morphology of the cryo formation inside the microstructure of GPC using a 4-D Low Temperature Scanning Electron Microscopic (4D-LTSEM). GPC specimens were frozen at -180 °C and were slowly sublimated to capture cryo creation in the paste. According to ASTM C666, nominal freezing temperature for PCC is -18 °C. So, the microstructure of GPC at -18 °C was investigated to find the applicability of ASTM C666 for paste tense. The results show that rate of cryo formation is slow from 0 °C to -18 °C indicating sufficient resistance of GPC when exposed to cold climates.