Comparative reactivity and microstructural characterization of mineral wastes in alkali activated binders

The development of alkali-activated materials (AAMs) based on mineral wastes and/or secondary raw materials (WSRM) as main binder components offers a great potential to increase material circularity and to reduce environmental implications related to material production. This study assesses the behavior of 6 Austrian WSRMs when utilized as major binder components alongside metakaolin (MK) (45 wt% WSRM/ 55 wt% MK) in potassium water glass activated binders. The utilized WSRMs comprised two types of steel slags, three types of construction and demolition waste including mineral stone wool, and glass waste. Highly functional binders with 90-day strengths ranging from 71 to 106 MPa were obtained. Nevertheless, the wide variety of setting behavior, strength, and microstructural characteristics revealed the distinct properties yielded by each WSRM. Steel slags showed relatively quick setting, high heat release, high strengths, and a strong indication on the coexistence of C-A-S-H gel with K(C)-A-S-H gel as the main binder phase. The other WSRMs exhibited longer setting times, lower early strengths and strength gain rates with indications of the dominance of K(C)-A-S-H gel phases in the reaction products. The outcomes of this paper foster the strong potential of the used WSRMs as primary AAM binder components and lays the foundation for further optimizations and investigation of WSRM-based AAMs.