With concrete continuing to be an important building material in 70 percent of constructions across the world, researchers are looking for innovative ways to make it smarter and work harder to help build better structures.

Scientia associate professor Wengui Li in the School of Civil and Environmental Engineering at UNSW Sydney is one such researcher looking to conquer concrete. With expertise in construction materials and structural engineering, his focus on concrete initially developed from an interest in seismic design, or helping buildings withstand earthquakes.

Self-sensing concrete

A 2023 survey in NSW found 53 percent of residential apartment buildings had a serious defect, and 7 per cent of those defects were structural.

Li’s team is testing cement-based sensors that can detect microscopic cracks in buildings so that they can be repaired before they impact structural performance.

Made of conductive materials, the sensors measure ‘piezoresistivity’, or a material’s change in electrical resistance when pressure or weight is applied. Hooked up to cables, the sensors send data that warns about cracks based on how dramatically the resistivity changes as power surges through the sensors.

The sensors could assist in the maintenance of large apartment buildings, says Li, performing better than other measuring methods such as strain gauges and optical fibres. Some of the advantages include high sensitivity, low cost and more durability.

Self-healing concrete

Another area of research by Li’s team revolves around reinforced concrete. When the steel inside reinforced concrete starts to rust due to moisture exposure, it can cause concrete cancer. When the steel expands, the pressure can cause the concrete to crack.

Li’s researchers have successfully added a crystalline mixture to concrete that has shown healing in hairline cracks after a fortnight. Using self-healing concrete not only means safer structures but also “has an added effect of reducing emissions by cutting down on cement production”, Li says.

This can improve the durability and extend the service life of concrete to more than 100 years.

New forms of concrete without cement

Sustainability is also being prioritised in construction with new research focussing on creating concrete without cement – one of the biggest emitters of carbon.

Geopolymer concrete does away with cement and instead uses by-products from the production of coal and iron mixed with a corrosive liquid. However, it’s a lot more expensive to produce than standard concrete.

“Cost must be measured against sustainability so other alternatives still need to be explored,” says Li. One option is waste glass, a large part of which currently ends up in landfill.

“To maximise the use of waste glass in concrete production, we have developed waste glass powder-based geopolymer concrete with a total glass content of over 80 per cent.”

Photocatalytic concrete

Researchers in South Korea used concrete to clean up the air in a busy tunnel by coating the road in titanium dioxide and subjecting it to light exposure. The process is called ‘photocatalysis’, where light is used to speed up a chemical reaction that turns pollution from vehicle exhausts into salts that are washed away by rain.

Similar to other innovations, production at scale is expensive. Li says photocatalytic concrete has “great potential to remove air pollutants caused by massive vehicle exhausts, providing clean air in our cities and towns. However it's still necessary to further improve its efficiency with new hybrid nano-photocatalysts”.

Energy storage concrete

US researchers are turning concrete into an energy storage system by making a battery with cement and carbon black. When added to the cement mixture, carbon black forms conductive branches in the porous holes made by cement as it reacts to water. By making two small plates of the ‘wired’ concrete, sealed together but separated by an electrolyte and membrane, they were able to store a small amount of power. The researchers are now working towards storing a day’s worth of energy for an entire house by building the foundation with their invention.

Li says the next 10-20 years will be big for concrete that does more than just provide a foundation.

“After trying to make concrete stronger and more durable, the next research will focus on the multifunctional. Soon, more and more innovations will be moved out of labs and into the field for commercialisation.”

Image: A/Prof. Wengui Li's cement-based sensors can detect microscopic cracks the naked eye can't see. Photo credit: R Freeman UNSW

Branko Miletic

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