Driven by cost and sustainability, secondary resource materials such as fly ash, blast furnace slag, and bottom ash are increasingly used for alternative types of concrete binders, such as geopolymers. Because secondary resources may be highly variable from the perspective of geopolymers, it is often a challenge to upscale these binder types to an industrial scale. This paper describes the testing of a screening method – feature sizing and chemical typing (FS&CT) using an electron microscope – in order to capture the heterogeneity of secondary resources in a quantitative manner. This automated technique is able to simultaneously measure inter particle variations in chemistry (energy dispersive X-ray spectra) and size (shape). Two key variables for application in geopolymers, Si:Al ratio and size, are measured using FS&CT for coal combustion fly ash and its fraction of potentially reactive aluminium-silicate particles. These measurements have been preliminary related to the reactivity of the fly ash in NaOH-solutions with high liquid/solid ratios as well as low liquid/solid ratios (geopolymers). As such the FS&CT method is found to be a useful alternative to commonly used bulk methods such as X-ray fluorescence (XRF) or manually operated electron microscopy that gives just an indication of local heterogeneity.Highlights► Feature sizing and chemical typing (FS&CT) is a new method for characterizing fly ash. ► FS&CT quantitatively measures inter particle variations in chemistry and size. ► FS&CT data can be used to assess fly ash reactivity in geopolymers.

•Geopolymers were made from fly ashes and waste Al etching solution as activator.•Compressive strength measured at 28 days R.T. curing varied from 51.3 to 84.3 MPa.•The geopolymers have low elemental leaching and can be suitable in construction.Combined management of coal combustion fly ash and waste aluminium anodising etching solutions using geopolymerisation presents economic and environmental benefits. The possibility of using waste aluminium anodising etching solution (AES) as activator to produce fly ash geopolymers in place of the commonly used silicate solutions was explored in this study. Geopolymerisation capacities of five European fly ashes with AES and the leaching of elements from their corresponding geopolymers were studied. Conventional commercial potassium silicate activator-based geopolymers were used as a reference. The geopolymers produced were subjected to physical, mechanical and leaching tests. The leaching of elements was tested on 28 days cured and crushed geopolymers using NEN 12457-4, NEN 7375, SPLP and TCLP leaching tests. After 28 days ambient curing, the geopolymers based on the etching solution activator showed compressive strength values between 51 and 84 MPa, whereas the commercial potassium silicate based geopolymers gave compressive strength values between 89 and 115 MPa. Based on the regulatory limits currently associated with the used leaching tests, all except one of the produced geopolymers (with above threshold leaching of As and Se) passed the recommended limits. The AES-geopolymer geopolymers demonstrated excellent compressive strength, although less than geopolymers made from commercial activator. Additionally, they demonstrated low element leaching potentials and therefore can be suitable for use in construction works.