Permeability recovery by self-healing of class F fly ash-based geopolymers

Alkali activated materials (AAMs), also known as geopolymers, have been proposed as lower carbon footprint alternative cementitious materials to ordinary portland cement (OPC). Geopolymers are formed from an aluminosilicate precursor, such as fly ash, mixed with an alkaline activating solution. These materials may have self-healing behavior, which makes them promising materials for applications where controlling crack widths is critical, such as in well bores or steel-reinforced concrete structures. In this study, the self-healing ability of a Class F fly ash-based geopolymer was investigated using a pressure transmission test (PTT) to measure the initial permeability of the material, the permeability after damage using freeze-thaw cycling to initiate cracks, and the permeability following post-damage curing to encourage self-healing. The geopolymer was found to have low permeability, 0.26 ± 0.09 µD at 28 days, which is comparable to reported values for OPC. The permeability increased after damage, but then decreased again after the self-healing curing period. The results show an inverse correlation between the level of initial damage and the level of permeability restoration upon self-healing. This work indicates that geopolymers can indeed self-heal cracks to reduce damage, suggesting that they are promising barrier materials for well construction and other applications.