Efficacy of Elevated Temperatures on Mechanical Properties of Concrete Containing Aluminum Slag from the Microstructural Perspective

Concrete structures undergo behavior change and instability at elevated temperatures. In most cases, these behavioral variations and instability are related to the changes in C-S-H and (C-A-S-H nanostructures, which is an important part of the cement paste hydration process and plays a crucial role in determining the strength and mechanical properties of concrete.. Application of aluminum dross as a type of pozzolanic material to cementitious composites can improve concrete behavior at elevated temperatures. Consideringly, this article aims to investigate the effects of elevated temperatures on concrete containing different percentages of aluminum slag from the microstructural perspective. For this purpose, cubic samples containing different percentages of aluminum slag powder were prepared. The specimens were cured in a humidity bath for 28 days and then heated for 60 min at temperatures of 25 to 750 °C. To evaluate the mechanical properties, the percentage of weight and compressive strength changes of concrete samples were investigated. Scanning electron microscopy (SEM) images were also used to observe the microstructural properties of the samples at different temperatures. According to the results, in samples containing slag less than 10% due to its activation as well as the hydration process and the formation of C-A-S-H and C-A-H nanostructures, the portlandite phase was formed which has improved the compressive strength. On the other hand, the elevated temperature and the occurrence of the dehydroxylation process lead to water decomposition within the bonds of C-S-H nanostructure which subsequently results in the change in compressive strength behavior.