Homing in on sustainable concrete with fly ash, slag and waste sands

Concrete. We need a lot of it, and it’s not environmentally sound to make.

Each year, the world uses around 30 billion tonnes, and production makes up 8% of global greenhouse gas emissions.

As such, the race is on to find better ways of making concrete.

The most recent suggestion, coming from an international team of researchers led by Flinders University, is making new geopolymers, stony materials made from aluminium, silicon and oxygen.

The researchers, who have published their study in Construction and Building Materials, have found that geopolymers developed with waste materials and renewable natural fibres perform just as well as conventional concrete.

“Instead of cement, in which production generates a high amount of carbon dioxide, we’re using fly ash, or slag, or any type of powders which are eco-friendly, as binder materials in the concrete,” says lead author Dr Aliakbar Gholampour, a lecturer in civil and structural engineering at Flinders University in Adelaide.

The researchers made geopolymer mortars with fly ash (a by-product from coal-fired power stations), furnace slag (a by-product of iron and steel making), and waste sands from lead smelters and glass production.

They reinforced these geopolymers with small amounts (1-2%) of natural fibres such as ramie, hemp and bamboo fibre.

Two people standing in a lab with long blocks of concrete roughly the size of their arms in front of them
Dr Aliakbar Gholampour, right, and PhD civil engineering candidate Zakir Ikhasi who use natural fibres, lead slag (black sand) and waste glass sand materials in new-age concrete mixes. Credit: Flinders University

“For making, we used the same process that we use for concrete production – however, after pouring the geopolymer material in moulds, they have different types of curing,” says Gholampour.

Next, the researchers are interested in improving the performance of their materials for different industries, as well as improving the process for making concrete – including using recycled waste as coarse aggregates, and even 3D-printing concrete.

“We recently purchased the first 3D printer for concrete in South Australia at Flinders University, and we are planning to do research on the use of the geopolymer in construction and 3D printing,” says Gholampour.

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