In New Zealand, concrete (of which cement is a key ingredient) was recently identified alongside steel as the highest-emitting building materials to make and use in the country.
A key takeaway in the report was the potential of low carbon cement alternatives. So, are we using these alternatives? The Fifth Estate checked in with high blend cements, geopolymer cement and a new technology used by LafargeHolcim that uses CO2 instead of water in the curing process.
The technological solutions are already available to make the move to low carbon cement for construction, according to University of Melbourne zero carbon researcher Michael Lord.
Sadly, he says there are still “huge institutional barriers” standing in the way of these low carbon options.
“We just need the incentives created to get there.”
He told The Fifth Estate that the big barrier is cost. Some commercially available low carbon alternatives remain around 10-15 per cent more expensive than the conventional version, even though there’s not always inherent reasons for the inflated prices.
The problem is that the demand just isn’t there. “These are still niche products.”
Another barrier is the legacy left by decades and centuries of using the standard Portland cement. Lord says there’s a perceived risk for taking on a novel material because of the potential of something going wrong.
A workaround on this issue would be some kind of risk-sharing mechanism, says Lord, where the government takes on some of the liability risk of using specified alternative materials.
The report on embodied carbon in NZ flagged government buildings as a good place to start on the materials decarbonisation journey.
It recommended using a life cycle assessment, such as that contained in Green Star, when specifying government building programs. It also suggested embodied carbon considerations in public and private procurement policies.
Lord was lead author of a 2017 report by climate change think tank Beyond Zero Emissions that would put Australia into a position to lead the world with a zero carbon cement industry.
It involved a suite of already commercialised technologies: geopolymer cements, high-blend cements and mineral carbonation.
- Lord presented on the topic at our Tomorrowland 2017 event – see our ebook for details
Pockets of low carbon concrete innovation but business as usual prevails
Despite a sluggish start on a low carbon concrete economy there’s been some pioneering uses of the concrete alternatives in Australia, including the Brisbane West Wellcamp airport that’s almost entirely built out a type of geopolymer cement.
Projects that showcase the benefits of alternatives to Portland cement can help further the cause, such as the maintenance-free bridges developed by Deakin University for Geelong park.
They will be made from geopolymer concrete with carbon and glass fibre reinforcement that should ensure the bridge requires no maintenance over its 100 year life-span.
By replacing the steel reinforced concrete that’s usually used with a more durable carbon and glass fibre reinforced polymer, new design should avoid the usual problem of corrosion that occurs in conventional steel reinforced concrete construction.
Lord says this is an “innovative use of two technologies to get to 100 years maintenance free.”
Geopolymer cement offers big upfront opportunities
Unlike with Portland cement, where 55 per cent of its emissions come from the chemical process of limestone calcination, the reactions involved in producing geopolymer cement do not release carbon dioxide.
One way of producing geopolymer cement is with fly ash (a by-product of burning coal) and ground granulated blast-furnace slag (a steel production waste product). The 2017 report said Australia had 400 million tonnes of fly ash stockpiled from over a century of coal-burning.
Geopolymer cement isn’t suitable for all uses but Lord says it has some inherent advantages over its conventional equivalent, such as greater resistance to heat and a lot of chemicals, and it can better protect steel.
Other cement alternatives
Beyond geopolymer cements, which rely on the existence of fly ash stores from coal plants– ultimately needing to be phased out – there’s other alternatives.
One promising option is high blend cements, where Portland cement is combined with as much as 70 per cent fly ash, slag, clay or ground limestone.
There’s also mineral carbonation, which involves reacting carbon dioxide with calcium or magnesium to produce a stable solid carbonate rock, locking away emissions.
LafargeHolcim is currently using a cement technology developed by Solidia Technologies’ that uses CO2 rather than water in the curing process.
The technology reduces the overall carbon footprint in precast concrete by 70 per cent and brings down the cement plant’s carbon emissions by up to 40 per cent.
Critically, it works within the existing systems of production – the normal cement kiln just needs the temperature to be turned down.
Less concrete = less embodied carbon
There’s also other materials that, where suitable, can replace concrete entirely. Engineered timber is one of them.
Capable of locking up carbon, sustainably sourced and managed timber products such as cross laminated timber are often suitable to replace concrete in above ground uses.
Clever engineering tricks to use less concrete is another way of keeping its environmental footprint down.