Two of our local councils are growing the circular economy by using waste glass as a sand substitute and to make concrete.
A win-win situation, as more than 1.5 million tonnes of used glass has to be disposed of each year and some 57 million tonnes of gravel, sand and cement has to be quarried each year to produce the concrete – an essential and ever-increasing component of modern society.
Glass consumption is at its highest in NSW, which produces about 460,000 tonnes of used glass per year. But domestic recycling programs are few and far between as the sorting of the different kinds of glass is complex and costly, and there are only small markets for the recycled glass so we pay to send the recyclable glass to landfill.
Lake Macquarie council is trialling the reuse of “glass sand” manufactured at a custom-built plant on the Central Coast.
It has similar applications to normal sand and can be used as bedding material in drainage projects and other civil works, potentially closing the loop on thousands of tonnes of glass each year.
Concrete can offer a new circular economy product for this waste glass in two ways. Port Stephens council is collaborating with local business Redicrete to produce Greencrete using crushed recycled glass in place of quarried sand and gravel. You can see the result on traffic islands at Tanilba Bay.
Recycled glass, when ground into a fine powder has pozzolanic activity similar to powdered fly ash and slag and can be substituted for a portion of the cement in concrete. This offers a win-win for both the reuse of the waste glass and the environment since production of cement, the primary binding agent of concrete, generates large amounts of CO2.
Using glass as a cement substitute would reduce the carbon footprint of concrete by 20-40 per cent, since grinding of glass into a pozzolanic powder uses much less energy.
Further, the experts tell me, the ground glass being a silicate material binds with the lime in the concrete mix and increases the strength and density of the concrete. Read more in Rethinking Cement from Beyond Zero Emissions.
Emeritus Professor Tim Roberts is from the School of Enviromental and Life Sciences at the University of Newcastle.
