Freezing-thawing durability and chemical characteristics of air-entrained sustainable concrete incorporated high-calcium fly ash in high-volume

Abstract

This study purposed to find the maximum fly ash replacement ratio, which can provide guaranteed freezing and thawing durability if the air is appropriately entrained, as well as an understanding of how increments of fly ash replacement influence the hydration products. Compressive strength and freezing-thawing durability were measured on concrete specimens. X-ray diffraction, thermogravimetric analysis, scanning electron microscope, and energy dispersive spectrum analysis were conducted on fly ash/cement pastes. Finally, the carbon footprint was estimated. Although the fly ash replacement ratio of 70 % is the lowest in strength and durability, it gives the highest strength per unit of CO2 emission. Freezing and thawing durability shows a significant dependence on the freeze-thaw environment. The relative dynamic modulus of elasticity has dropped off considerably when tested in Procedure A (freezing and thawing in water) and this drop was not observed in Procedure B (freezing in air and thawing in water) even at 1200 freezing-thawing cycles. Chemical analyses on pastes showed similar patterns in all replacement levels, confirming that there is no significant change in mineralogy even at the 70 % FA replacement, but the intensity of the portlandite peak decreases with increasing replacement ratio. Increasing fly ash decreases residual portlandite due to pozzolanic reaction, thereby, hydration products with a reduced Ca/Si atomic mass ratio have been formed.