Geopolymer concrete from regional waste streams

What are geopolymers?

Geopolymers are formed by the alkali activated polymerisation of an aluminosilicate precursor. They offer significant environmental advantages when used as a replacement for ordinary Portland cement (OPC). Production of geopolymer cement may result in significantly less carbon dioxide emission into the atmosphere than the production of OPC, whilst offering a product with improved characteristics, such as compressive strength and chemical resistance.

Geopolymers are synthesised by polymerisation of aluminosilicate precursors in an alkali medium and are an amorphous network of AlO₄^- and SiO₄ tetrahedra linked alternately by sharing oxygen atoms. Positive ions, such as Na⁺, K⁺, Li⁺, and Ca²⁺, in the framework are required to balance the negative charge of Al³⁺ in IV-fold coordination with oxygen. The empirical formula is M_n[(SiO₂)_z-AlO₂]_n·wH₂O (where: M_n is a cation, usually an alkali, n is a degree of polycondensation, w ≤ 3 and z is 1, 2 or 3).

The fabrication of various precursors can be achieved by (a) calcining aluminosilicate minerals (eg clay minerals such as kaolinite, (Si₂O₅,Al₂(OH)₄)), or (b) condensation of SiO₂ and Al₂O₃ vapours. Alternatively a number of processes produce aluminosilicates as a waste or by product, such as fly ash from combustion of coal for power generation, and can supply aluminosilicates required for the synthesis geopolymer. There are a wide range of aluminium and silicon-containing minerals that could serve as potential precursors for synthesis of geopolymers, including mine and minerals processing wastes.

About this project

We are investigating the suitability of a range of soluble aluminosilicate bearing waste streams for use as geopolymer concrete feedstocks. A range of experimental and analytical techniques is therefore being used to better understand the structure-chemistry-property relationships of geopolymers. We are currently producing geopolymers using a variety of waste streams (fly ash and kaolin) available from the Kwinana Industrial Region, Western Australia.

The project aims to develop the necessary chemical and structural understanding of geopolymers made from waste products for them to be used to capture a significant share of the ready mixed and precast concrete market for a given industrial region. The overall objectives are to:

• Assess the suitability of soluble or dissolvable silica bearing waste streams generated in any one geographical region, to be used as geopolymer feedstocks
• Determine the role that secondary metal ion constituents in the geopolymer process play on the kinetics of formation and resulting microstructure of geopolymers
• Design, manufacture and test commercially viable ready-mixed geopolymer concrete made from the suite of regionally generated wastes
• Investigate the long-term durability of such concretes

The NRI directly leads several major milestones within this project, including:

• Obtaining funding from new industry partners
• Studying a wide range of mixtures maximizing waste components from the region
• Impact of secondary metal ions on the geopolymerization processes and the kinetics of these reactions, with and without applied heat, and their effects on the setting times and curing of geopolymer concrete

About the CSRP

This large research project forms part of the Cooperative Research Centre for Sustainable Resource Processing (CSRP) and involves partners from industry, universities and government. The aim is to develop the necessary chemical and structural understanding of geopolymers made from waste products to allow them to capture a significant market share of the concrete business for a given industrial region.