Long-life low-carbon concrete switches 80% of its cement for coal ash

Long-life low-carbon concrete switches 80% of its cement for coal ash
Dr. Chamila Gunasekara holds a sample of the low-carbon concrete
Dr. Chamila Gunasekara holds a sample of the low-carbon concrete
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Dr. Chamila Gunasekara holds a sample of the low-carbon concrete
Dr. Chamila Gunasekara holds a sample of the low-carbon concrete
Eraring Power Station is dwarfed by its enormous ash dam
Eraring Power Station is dwarfed by its enormous ash dam

RMIT researchers have developed a new type of "green concrete" that incorporates twice as much recycled coal ash as existing low-carbon concretes, halves the amount of cement required, and lasts even longer than regular Portland cement concrete.

Coal ash is abundant around coal-fired power stations. In fact, that might be considerably understating things – globally, power stations produce around 1.2 billion tonnes annually, and in Australia coal ash accounts for nearly 20% of all waste. It's a staggering figure – and it's also a safe bet that this stuff will remain abundant long into the renewable energy transition.

Hence, it's an enormous potential material resource, and low-carbon concrete manufacturers have been using it as a cement substitute, typically replacing up to 40% of the cement. In an environmental sense, this kills two birds with one stone, making use of a massive waste product while cutting down on cement – which by itself accounts for somewhere around 8% of all global carbon emissions.

A team from RMIT has been working with the Ash Development Association of Australia, and the AGL Loy Yang Power Station, to make better use of this dubious asset, attempting to push the ash content up to replace over 80% of the cement.

To do so, the researchers used a mixture of low calcium fly ash, with 18% hydrated lime and 3% nano-silica acting as strengthening agents, then poured some concrete and started testing its mechanical properties.

The resulting High-Volume Fly Ash (HFVA-80) concrete demonstrated a compressive strength increase from 22 to 71 MPa between days 7 and 450. It achieved flexural strengths of 2.7-8.7 MPa, splitting tensile strengths of 1.6–5.0 MPa and an elastic modulus of 28.9–37.0 GPa. It outlasted regular Portland cement over time when exposed to acids and sulphates for two years.

"Our addition of nano additives to modify the concrete’s chemistry allows more fly ash to be added without compromising engineering performance,” said project lead Dr. Chamila Gunasekara, from RMIT’s School of Engineering, in a press release.

Eraring Power Station is dwarfed by its enormous ash dam
Eraring Power Station is dwarfed by its enormous ash dam

Better still, the team says it sees the technique doesn't require fine 'fly ash' and appears to work about as well with low-grade 'pond ash,' having now created and tested structural concrete beams from the latter, which have passed Australian Standards certification for engineering performance.

“It’s exciting that preliminary results show similar performance with lower-grade pond ash, potentially opening a whole new hugely underutilized resource for cement replacement,” says Gunasekara. “Compared to fly ash, pond ash is underexploited in construction due to its different characteristics.

"There are hundreds of megatonnes of ash wastes sitting in dams around Australia, and much more globally. These ash ponds risk becoming an environmental hazard, and the ability to repurpose this ash in construction materials at scale would be a massive win.”

The RMIT team has also worked with Hokkaido University to develop a pilot computer modeling system forecasting the performance of these new concrete mixtures over time, and the team hopes to use this software to analyze and optimize further new mixes.

Source: RMIT

Now if the Aussies would develop a scalable fission reactor/power module that can be made from this concrete (there are additional requirements for nuclear plant concrete from what engineers have told me), then it will be a win-win for both concrete, for the waste fly ash dumps, and for the "green" revolution in battery powered vehicles. One day maybe there will be modular fusion power plants, it would be nice to have options for construction in a central location. So - is this concrete lighter or heavier than the standard building material? Will the cost be a factor if cast & set in a factory like bridge beams are? We need more incremental gains like this! Thanks
Sounds great. Hope demand for freshly made coal ash doesn't make it more profitable to burn coal.
How much you want to bet this formulation has the same problems with leeching mercury, cadmium, and arsenic other fly ash formulations have? Like, I want Greener concrete, but not something like this in my house
I wonder how strong the new concrete is. The sample he is holding did not seem to cure evenly; the top half is filled with bubbles and the bottom half looks more solid. I would be curious to see the test results for this concrete to see how it compares to a traditional Portland mix.
One of the old statistics I remember (from the '90s, I believe) was that there was more uranium in coal and that more radioactivity was released into the air from coal-fired power stations than from any nuclear power plant. They have probably sequestered that by now, but I'd like to see it looked into before they put megatonnes into buildings, thanks.
Do not see what is "new" here. It is known from centuries.
The main factor in cement production is higher temperature the ingredients are "baked" under.
The best concrete ever is the Roman, because was prepared with ashes from Vesuvius, can imagine the temperature.
From the very beginning of the Portland cement, producers are trying to save in the burning process.
So using coal ashes is logically effective.
Wasn't there problem somewhere (England?) where some of this similar aggregate caused problems in a housing or school bidg project that faced being condemned because the "cement" failed, in a variety of ways? (Reactively, structurally, chemical and waste emissions.)
faulty logic
Very inspiring. Nano material @ 3% may be what keeps the price parallel or above current cement price? Is exhibits higher standards we read. This tells us from the inception it's a higher grade material and costs will always be kept commensurate. The other aspect we can derive from comments below is, the contamination present in coal ash. Ranging from radioactivity to heavy metals, in abundance. So there may be nothing gained by handling these vile wastes. Worse than electric vehicles there being a saturation point sourcing the battery materials, This sounds like a very clever idea, with an enormous degree of research to be completed to enable a presentable proposal?