Waste to alkali-activated binders (WIN)

The construction sector represents one of the most significant sources of waste generation in the European Union and recent data indicate that 9 % of all greenhouse gas emissions generated worldwide originate from the manufacturing of construction materials. In parallel to the increased knowledge on construction materials environmental impacts, the concept of circular economy emerged, which can be understood as a regenerative system in which resource consumption and emissions are minimized by slowing, closing, and/or narrowing material and energy loops. Considering this, the development of strategies to utilize mineral wastes in construction materials exhibits high potential. In this context, so called alkali-activation technology presents one highly promising approach. In the most general description, alkali-activated materials (AAMs), also often referred to as geopolymers, consist of two main components a mineral precursor and an alkaline activator (solution). When mixed AAMs can be used similar to concrete, exhibiting alike workability properties. There are many types of raw materials potentially applicable to be used for AAM production, such as treated natural rocks (e.g. metakaolin, calcinated clays, volcanic ashes), industrial by-products from coal and steel industry (e.g. fly ashes and slag), as well as different Si and Al-rich wastes (e.g. concrete demolish wastes, incineration ashes, mineral wools). Depending on the raw materials choice, the properties of AAMs may differ widely, and can thus be tailored for different applications. The main objectives of this project are to investigate fundamental material behavior of 6 major inorganic waste streams, when used as AAM precursors and raw materials for alkaline activator syntheses. Therefore, initially the chemistry and mineralogy of the wastes will be characterized. As a next step, experimental setups for activator syntheses will be developed to understand material dissolution behavior in alkaline (= high pH) conditions. Relevant experimental parameters are temperature, pressure, exposure period and pH. During these experiments, potential environmental harmful elements, such as heavy metals, may be chemically extracted (e.g. precipitated). Developed waste- based alkaline activators will be mixed with waste precursors to produce AAMs. Characteristic material properties, such as, strength, porosity and basic durability aspects (leaching behavior and acid resistance), will be characterized in order to understand the fundamental functionality of the novel systems. Findings of the project form the basis for future development of industrial exploitation strategies of large local waste deposits to be utilized in the construction industry, following the overall strategy for a climate neutral economy by 2050. The project will be conducted in close collaboration between Graz University of Technology (Austria) and the Slovenian National Building and Civil Engineering Institute.