Synthesis and characterization of alkali activated foams based on different waste

Alkali-activated materials, also called geopolymers, are an environmentally friendly and technically acceptable alternative to cement, concrete, and ceramics. In order to produce AAM, precursors containing (i) SiO2 and Al2O3 in sufficient quantities and in a reactive form-glassy state (e.g. ash, activated clay), and (ii) alkaline activators in a solution (mostly NaOH, KOH, Na-water glass, K-water glass) are needed. When these two components are mixed, firstly, the dissolution and transport of the components (Al, Si) in the alkaline activators takes place, and then, through poly-condensation of the Al and Si, an aluminosilicate network is formed, which can be amorphous or partially crystallized.

Suitable precursors for AAM are thermally activated clay, natural pozzolan (e.g. volcanic ash), as well as different kinds of industrial waste, such as ashes (fly ash, bottom ash, bio-based ashes) and various slags. Many products can be obtained by the alkaline activation process which could replace traditional construction products. They range from blocks, slabs, paving-stones, curbs, and partitions, to refractory materials and materials for specific industrial applications (e.g. insulation plates).

Foams, which are produced when appropriate foaming agents are added to an alkaline activated sludge, are one of the most promising types of alkali-activated materials due to potentially higher added value. Such foams are non-combustible and dimensionally stable, and have high strength and good insulation properties.

The main objective of this project is to develop new lightweight alkali-activated foams based on the mixture of various secondary raw materials (fly ash from Thermal plant Šoštanj and different waste glass). Different foaming agents and stabilising agents (in varying proportions) will then be investigated in order to achieve the highest possible porosity (Al powder, H2O2, NaOCl, SDS). In addition to the use of waste materials, the additional advantage of such foams (in comparison to commercially available inorganic foams) will be that they will be produced at temperatures lower than 100 °C, and they will be stable also at elevated temperatures (expected up to 1000 °C).

To achieve these goals, focus of project will be on:

– identification of local waste flows to be used in alkali activated production,

– selection of proper combinations of solid waste precursors and alkaline activators by DOE (Design Of Experiment) approach to obtain optimal characteristics,

– finding of optimal foaming agents and foam stabilizing agents in order to obtain highly porous structure,

– characterization of foams at room temperature and at elevated temperature (up to 1000 °C),

– quantification of the environmental footprint of the new technology and products by life cycle assessment (LCA).

Project is divided into six work packages related to the specific goals of the project, and it will be performed by ZAG –Department of Materials and IJS – Department of Advanced Materials. Both groups are already highly experienced in the preparation and quantification of foamed materials of different origins.

The acquired knowledge will provide the basis for the development of various new products by using precursors that are currently landfilled and potentially harmful to the environment. Furthermore, new interdisciplinary knowledge, combining technical properties with environmental aspects will be obtained for the designing of alkali activated materials from different precursors (fly ash, slag, glass).

This project has received funding from the Slovenian Research Agency (ARRS) under the project grant J2 9197: “Synthesis and characterization of alkali activated foams based on different waste”.


  • Slovenian National Building and Civil Engineering Institute
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  • Institut Jožef Stefan
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