Role of Secondary Precursors for Improving the Performance of GGBFS-Based Alkali-Activated Matrix: A Systematic Review

The United Nations is endeavoring for global sustainable development. Consequently, researchers have directed investigations around alkali-activated matrix/material (AAM). GGBFS-based AAM has shown enormous potential to replace cement-based matrix; however, the difficulties encountered in GGBFS-based AAM are low workability, faster setting time and high risk of efflorescence, which are generally addressed using secondary precursors. Various international standards are also available, which serve as guidelines for development of AAM. Bureau of Indian Standard (BIS) has also come up with IS 17452: 2020, which serves as a guideline for development of alkali-activated concrete. But, the scope of IS 17452: 2020 lists GGBFS, fly ash, metakaolin, calcined clay and silica fumes as the only precursor materials for AAM. It explicitly recommends the use of GGBFS-Fly ash combination for alkali-activated concrete. Different secondary precursors with varying chemical composition and intrinsic properties have been used to overcome the issues in GGBFS-based AAM. The different intrinsic properties, especially the chemical composition and reactivity of secondary precursor affect the behavior of GGBFS-based AAM differently. The effect of these secondary precursors, classified into three different categories based on chemical composition criteria, has not been previously reviewed for GGBFS-based AAM. Therefore, the present article is an attempt to review the effect of each category of classified secondary precursor on GGBFS-based AAM. Initially, all secondary precursors were classified into high calcium aluminosilicates, low calcium aluminosilicates and siliceous precursor categories. The effect of including secondary precursors of a particular category on fresh properties, mechanical properties, efflorescence, transport properties, durability properties and microstructure of GGBFS-based AAM has been reviewed. The key findings of the review state that the material having CaO percentage greater than GGBFS actually behaves as a high calcium aluminosilicate precursor, whereas material having CaO percentage less than GGBFS behaves as low calcium aluminosilicate precursor, in GGBFS-based AAM. This review will help engineers, researchers, other professionals, etc., in classifying the material into different categories of precursor classification. It will also help in the judicious selection of secondary precursor from the appropriate category for enhancing the desired properties of GGBFS-based AAM. Moreover, the outcomes of the review will also help in upgrading IS 17452: 2020.