Glass cUllet conversIon To wAteRglass and used, with cement bypass flue dust, for cementless concrete building products (GUITAR)

Geopolymer concrete is an alternative to cement-based concrete. Most geopolymers are activated by sodium silicate, otherwise known as waterglass. However, this commodity product – used for processing textiles and lumber and in the manufacture of ceramics and paper – is formed using an expensive, high-temperature, energy-intensive process.

With funding from the Transforming Foundation Industries Challenge, the GUITAR project aimed to identify how sodium silicate could instead be manufactured in a lower-carbon way using waste glass – providing the potential to create a more environmentally friendly concrete and cost-efficient production for this valuable bulk chemical.

The project, led by recycling company Re-Gen Group working with the School of Natural and Built Environment and the School of Chemistry and Chemical Engineering at Queen’s University Belfast (QUB), explored manufacturing processes for sodium silicate made from waste glass.

“With recycled glass from bottle banks and household collections, you get a lot of breakages, resulting in small fragments that are difficult to identify. They either end up as low-value aggregate or landfill – in the UK, almost 200,000 tonnes of glass is sent to landfill each year,” explains Louth McMahon, Technical Development Manager, Re-Gen Group.

“Queen’s University Belfast had developed processes to turn waste glass into sodium silicate at much lower temperatures than conventional production – 150°C rather than 1000°C – so we worked with them to see if this could be done at scale.”

“Simple filtration removed a large amount of contaminants, producing a product with purity levels similar to commercially available products used in adhesives and detergents.”

The project investigated whether this sodium silicate was suitable for producing concrete products when used together with other foundation industry waste streams, including flue dust and blast furnace slag. Trials on its potential found it performed competitively with commercially available activators.

The team then ran factory trials on the resulting concrete products – including building blocks, normal density blocks, and a pre-bagged one-part binder – demonstrating the sodium silicate’s potential to produce low-carbon building products.

While the purity of sodium silicate is not a significant factor for its use in concrete, other industrial applications – such as detergents – require a product free from contaminants. So, another important area of work was on purification.

“We were able to show that simple filtration removed a large amount of contaminants, producing a product with purity levels similar to commercially available products used in adhesives and detergents,” says Marios Soutsos, Professor of Structures and Materials at QUB.

As a result of the project, Re-Gen Group are in discussions with two UK-based manufacturers regarding the potential for the waste-glass sodium silicate to be used in production processes. “Currently, the majority of sodium silicate is imported from Asia. This technology offers the opportunity to take waste products from here in the UK and produce a very useful chemical. It could reduce an industry’s carbon footprint and susceptibility to market volatility,” adds McMahon.

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