Influence of Sulfuric Acid Exposure on Mechanical Properties of Alkali-Activated Concrete

Abstract

This study focuses on investigating the relationship between binder chemical composition, microstructure development in alkali-activated paste (AAP), and the sulfuric acid resistance of alkali-activated concrete (AAC). Experimental analyses, including x-ray diffraction, thermogravimetric, and scanning electron microscopy (SEM) tests, were performed on the AAP to understand the impact of critical chemical compositions on the formation of hydrotalcite, portlandite, CSH, and CASH during the alkali-activation process. The sulfuric acid resistance of AAC was evaluated through various tests, including compressive strength, porosity, chemical titration analysis, and weight loss tests. These tests aimed to assess the ability of AAC to withstand sulfuric acid attacks and investigate how the binder’s chemical composition influenced its resistance to acid exposure. The results revealed that higher alumino-silicate ratios (Al/Si) and magnesium oxide (MgO) content in the binder composition led to increased amounts of hydrotalcite and CASH in the alkali-activated system when zeolite and metakaolin were used as replacement materials for slag. The AAC specimens with slag and metakaolin showed lower porosity at the same replacement ratio. The increased amounts of hydrotalcite and CASH in the AAC microstructure contributed to a reduction in the concentration of sulfate ions penetrating the AAC, leading to improved sulfuric acid resistance. This information can contribute to optimizing binder formulations for improving AAC’s mechanical properties and durability in corrosive environments. Concrete samples containing metakaolin and synthetic zeolite tested throughout this research project can be utilized in different construction and civil engineering applications, all with differing degrees of suitability. Metakaolin and synthetic zeolites can be used as a slag replacement in concrete samples and used in masonry bricks, commonly used in masonry walls, columns, and partitions. Furthermore, load-bearing or nonload-bearing masonry structures for building and civil engineering can also adopt the incorporation of AAC. Metakaolin and synthetic zeolite types utilized in this research project could also be applied to produce slag granular mixtures for use in the construction of roads and airfields. The requirements for the relevant constituents, composition and laboratory performance classification are specified in BS EN 12390-1:2019.