Application of fly ash-based geopolymer as an alternative for plug and abandonment

In this study fly ash-based geopolymers were produced by the alkali-activation of fly ash. The purpose was to use fly ash-based geopolymers as alternative for cement for plug and abandonment operations. Ultrasonic Cement Analyzers (UCAs) were used to investigate the instantaneous strength development and Uniaxial Compressive Strength tests were performed to compare the results with the UCA results. Several different recipes were made for the UCA tests and the compressive strength development for each recipe was measured. Adjustments were made to the recipe after each experiment to optimize the ingredients and increase the maximum compressive strength. When the final recipe was found, the obtained result from the UCA was tested in several UCS tests. During the experiments several different materials were used. However, it was found from the UCA results that the recipe containing only fly ash and alkali activators gave the best results; a continuous positive trend in the compressive strength development. The UCS tests showed higher compressive strength for the same recipe, indicating that the recipe had promising properties. During the UCS tests it was also found that a higher concentration of sodium hydroxide resulted in higher compressive strength. The results found in these experiments indicate that there is a potential to use fly ash-based geopolymers as an alternative cementing material for plug and abandonment. However, there is a need for further research on the subject before the geopolymers can be used in practice