New modeling has shown that low-carbon concrete developed at RMIT University could recycle twice the amount of coal ash compared to current standards, halve the amount of cement needed and deliver superior performance over time.
In 2022, coal-fired power plants produced more than 1.2 billion tons of coal ash. In Australia, coal ash makes up almost a fifth of all waste and will remain abundant for decades to come even as we transition to renewable energy.
Meanwhile, cement production accounts for 8% of global carbon emissions, and demand for concrete, which contains cement as its main ingredient, is also rapidly increasing.
To tackle both problems head-on, engineers at RMIT partnered with AGL's Loy Yang Power Station and the Australian Ash Development Association to replace 80% of the concrete cement with coal fly ash.
RMIT project leader Dr Chamila Gunasekara said this represents a significant advance as existing low-carbon concrete typically replaces no more than 40% of the cement with fly ash.
“Adding nano-additives to modify the chemical properties of concrete allows us to add more fly ash without compromising engineering performance,” said Gunasekara, of RMIT's School of Engineering.
Finding new opportunities in overlooked pond ashes
Comprehensive laboratory studies have shown that the team's approach also makes it possible to harvest and repurpose low-grade and underutilized 'pond ash' from power plants' coal slurry storage ponds with minimal pretreatment.
A large concrete beam prototype was built using both fly ash and pond ash and found to meet Australian standards for engineering performance and environmental requirements.
“It’s exciting that our preliminary results show similar performance to low-grade pond ash, potentially opening up a completely new, untapped resource for cement replacement,” Gunasekara said.
“Compared to fly ash, pond ash is underutilized in construction due to its diverse properties. There are hundreds of megatons of ash waste in dams across Australia and much more globally.”
“These ash ponds risk becoming an environmental hazard, and the ability to recycle this ash into building materials on a large scale would be a huge win.”
New modeling technique reveals long-term resilience of low-carbon concrete.
A pilot computer modeling program developed by RMIT in collaboration with Dr Yogarajah Elakneswaran of Hokkaido University has now been used to predict the performance of these new concrete mixtures over time.
According to Dr Yuguo Yu, an expert in virtual computational mechanics at RMIT, a long-standing challenge in the field has been understanding how newly developed materials can stand the test of time.
“We have now created a physics-based model to predict how low-carbon concrete will perform over time. This gives us the opportunity to reverse engineer and optimize mixes based on numerical insights,” Yu said. explained:
This pioneering approach was recently published in the journal cement and concrete research — Shows how the different components of new low-carbon concrete interact over time.
“For example, we can see how the fast-curing nano-additives in the mixture act as performance enhancers in the early stages of curing, compensating for the large amounts of slow-setting fly ash and pond ash in the mixture,” says Gunasekara. .
“The inclusion of ultra-fine nano additives significantly improves the material by increasing density and compactness.”
This modeling, which is broadly applicable to a variety of materials, represents a significant step forward toward digitally-assisted simulation in infrastructure design and construction.
By leveraging this technology, the team aims to instill confidence in local councils and communities in adopting new low-carbon concrete for a variety of applications.
This research was conducted by the ARC Industrial Transformation Research Hub (TREMS) to transform recycled waste resources into engineered materials and solutions for the circular economy. Led by RMIT's Professor Sujeeva Setunge, TREMS brings together top scientists, researchers and industry experts from nine Australian universities and 36 states, industry and international partners to minimize landfill waste and recycle recycled materials for construction and advanced manufacturing.