Innovative Use of Hazelnut Shell Ash as an Alkali Activator: A Comparative Analysis with Commercial Activators

The selection of alkali activators is crucial in determining the characteristics of alkali-activated materials (AAMs). The activators are typically derived from commercial sources and significantly affect the ecological impact of AAMs across different life cycle categories. Hence, this study investigated the utilization of hazelnut shell ash (HNA) as an alternative activator in the synthesis of AAMs for the first time. HNA is evaluated as a green waste-derived option in place of sodium hydroxide (NaOH) and potassium hydroxide (KOH) in blast furnace slag (BFS) activation. A comparative investigation was conducted on the fresh, mechanical, and microstructural properties of AAMs activated with HNA, NaOH, or KOH. The experimental results showed that the compressive strength of HNA-activated AAM specimens can reach up to 26.8 MPa at 28th days, equivalent to mixtures activated with 2.0M NaOH and 2.2M KOH. It was observed that HNA alleviates the early-stage reactions by providing sufficient alkalinity due to its K2O content, contributes to gel formation with its calcium and silicon rich chemical composition, and also improves the compressive strength by acting as micro-aggregate.