AUSTRALIA - Australian leadership: zero carbon cement possible in 10 years

Source: Cameron Jewell, The Fifth Estate

The Rethinking Cement plan, launching in Newcastle tomorrow, (Friday) finds that Australia can enjoy a zero carbon cement industry in 10 years using already commercialised technologies, such as geopolymer cements, high-blend cements and mineral carbonation.


The report lists three strategies that can get Australia to a zero carbon cement industry in 10 years, and a further two strategies that can see us go beyond into positive-carbon solutions.

Currently cement contributes about eight per cent of all global carbon emissions. About 55 per cent of the emissions come from the chemical process of limestone calcination, which releases carbon dioxide as a waste product, and is unavoidable if we use limestone-based cement. Next, 32 per cent comes from burning fuel to drive the process, and the remaining 13 per cent is indirect emissions from electricity used for grinding and moving materials around a plant.

Geopolymer cements

The first strategy in the plan is to supply 50 per cent of cement demand with geopolymer cement, as the reactions involved in producing the cement do not release carbon dioxide.

One way of producing geopolymer cement is with fly ash and ground granulated blast-furnace slag (a steel production waste product), with the report saying Australia had 400 million tonnes of fly ash stockpiled from over a century of coal-burning.

“These stockpiles, which currently present an environmental problem, should be valued as one of our most readily available mineral resources.”

Setting up a geopolymer cement production facility did not require a kiln, and cost less than 10 per cent of a traditional Portland cement facility.

Jobs could be created – where they’re needed

It could also provide jobs for communities struggling with the closure of coal plants.

“New plants can be established at or close to sources of stockpiled fly ash, potentially forming part of transition planning for local communities impacted by the closure of coal-fired power stations.”

However, a shift to metakaolin (clay) based production would eventually need to occur as coal-fired plants were closed down and fly ash stocks diminished.

Geopolymer cements produce 80 per cent less emissions than Portland cement, and with a zero carbon energy supply, this could be reduced to zero.

High-blend cements

Blending Portland cement with other materials to reduce its carbon intensity is the next strategy proposed.

While materials today are commonly added to cement to reduce emission (20-30 per cent), it is proposed that the proportion of replacement material is raised to 70 per cent – using fly ash, slag, clay and ground limestone to create a “new generation of high-blend cements”.

“Seventy per cent substitution is ambitious but achievable, as real-world examples … have already employed as much as 68 per cent fly ash, and more than 80 per cent slag.”

However, the report notes that some cements used for high strength concrete applications may need to have more Portland cement clinker.

“One advantage of a strategy based on high-blend cements in the short term is that it can be adopted using existing cement manufacturing equipment, requiring only marginal investment,” the report says. “An additional advantage is that it complements the geopolymer strategy by using the same raw materials.”

Mineral carbonation

While the first two strategies combined will reduce Portland cement use to 15 per cent of current demand, there’s still residual emissions to get to zero carbon.

A “carbon capture and utilisation” process, mineral carbonation, is suggested as the third strategy, and involves carbon dioxide reacting with calcium or magnesium to produce a stable solid carbonate rock, locking away the emissions.

“Mineral carbonation could prevent 95 per cent of cement kiln emissions from escaping to the atmosphere,” the report says.

The process has significant advantages over traditional carbon capture and storage, with no risk of leaking, the ability to be used at any location without having to find suitable geology, and because the products created have commercial value, such as magnesium carbonate and silica.

Magnesium silicates recommended for Australia are available in abundant serpentine mineral reserves.

Minimisation and the move to timber

The report also recommends reducing cement demand by at least 14 per cent by 2027, part of which could be achieved by building more timber buildings, already happening across the country.

The first part of this strategy involves increasing efficiency in design. This can be achieved by using software to design structures to use concrete more efficiently without compromising structural resilience. It can also be done by using high-strength concrete, which while typically requiring a higher cement percentage, can significantly reduce the amount of overall concrete needed.

Next is a plan to make 20 per cent of buildings timber.

“Our 10-year timber strategy is to replace seven per cent of the Australian cement market,” the report says.

“[Engineered wood products] can be used to build almost any new structure up to 20 storeys including offices, apartments, schools, libraries and retail outlets, while sawn timber can be used for buildings up to eight storeys. In the short term the biggest market for timber is likely to be multi- storey apartments.”

The report says over 10 years 1.4 million tonnes of carbon dioxide could be sequestered.

Carbon negative cements

The final strategy involves investigating the possibility of magnesium oxide cements, which could “capture significant amounts of carbon dioxide when manufactured and as they cure and age, meaning they have the potential to be carbon negative”.

The report says, however, there is currently a lack of research dedicated to the material’s development, and performance and durability is not yet proven.

“Magnesium-based cements are not sufficiently developed to be part of our 10-year strategy. Over the longer term, however, they have the potential to transform our cities into carbon sinks.”

New opportunities for industry

The report, which contains a number of case studies, detailed research on material availability is the beginning of a new series for BZE finding pathways for the industrial sector to continue making materials and chemicals without the emissions.

The sector has been “largely ignored” compared to energy, buildings and transport, the report says, though it is the source of 30 per cent of global emissions (and 21 per cent of Australia’s emissions).

“Without decarbonising industry, we stand little chance of achieving the Paris goals.”

The Zero Carbon Industry Plan will also tackle renewable heat for industrial processes; making steel without coal; and reducing waste and improving efficiency.


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