Concrete’s journey towards (net) zero carbon

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Concrete NZ launched in 2017, with one element of its Strategic Charter being to develop a sustainability position to help industry drive decarbonisation. A Sustainability Committee was established, and the following contains excerpts from its first paper.

Concrete NZ supports the Climate Change Response (Zero Carbon) Amendment Bill, and its objective to ensure New Zealand plays its part in reducing greenhouse gas emissions under the Paris Agreement.

The proposed legislation, which has just become law before the end of 2019, establishes a defined, long-term emissions target, with a pathway steered by medium-term emissions budgets and guided by an independent Climate Change Commission.

Concrete NZ’s support was offered despite the fact that cement clinker manufacture is an inherently carbon-intensive process, and cement companies are currently unable to reach zero carbon emissions with existing technology.

This is because the manufacturing process is driven by the base chemical reaction resulting from the decarbonisation of limestone.

The reason Concrete NZ is buoyed by the future is that significant steps have already been taken, domestically and globally, on the journey towards (net) zero carbon, and that progress will continue as the New Zealand concrete industry strives to decarbonise further.

Background 

The concrete industry plays a key part in the New Zealand economy, employing more than 7000 people across 190 concrete plants and 22 cement manufacturing and distribution facilities across New Zealand.

The industry is currently producing record levels of concrete (4 million cubic metres per annum) using locally-sourced aggregates, recycled water and either locally manufactured or imported cement.

Over the past several decades the industry has been particularly conscious of its environmental impact, and has been implementing initiatives to reduce CO2 emissions.

These initiatives include the increased use of mineral addition and supplementary cementitious materials (SCMs) in cement, the use of alternative kiln fuels in cement manufacture, and a general shift to more efficient cement manufacturing processes.

Overall, these new practices have reduced the embodied CO2 in concrete by 10% between 2005 and 2018, despite an increase of 13% in concrete manufacture, and an 18% increase in population.

In addition to focusing on CO2 generating processes, the industry has also worked to enhance its environmental practices by diverting/recycling waste streams, including returned concrete, away from landfill and into usable construction products.

Despite these recent positive developments, across central and local government, media and public mindsets, concrete is seen by some as a “polluter”.

Concrete NZ says the emergence of these perceptions are headwinds, an understanding of which will enable the concrete industry to develop strategies that set meaningful objectives, determine appropriate tactics and mobilise sufficient resources.

The New Zealand position 

The key challenge for the New Zealand concrete industry to do the same is addressing the fact that it accounts for a notable percentage of the country’s CO2 ledger — although this is skewed somewhat by New Zealand’s renewable energy generation capacity compared to other countries.

The industry is also discrete and isolated, and therefore relatively easy to control in terms of setting emissions reduction targets.

The government’s agenda has been set as New Zealand is a signatory of the Paris Agreement.

This carries obligations to reduce 2005 emissions levels by 30% by 2030, with the goal to limit the temperature rise to 1.5°.

Preliminary investigations show that in 2005, concrete in New Zealand was responsible for approximately 1.6 million tonnes of CO2, but by 2018, despite increases in production and population, this total had dropped by 10%, to just over 1.4 million tonnes.

This was achieved through supply chain modifications, kiln fuel optimisation, and the uptake of limestone filler in cement to reduce the clinker factor. This is an admirable achievement, and something the industry should be very proud of.

New technologies

In addition to alternative fuels to fire cement kilns, traditional SCMs and Class N pozzolans, there are several technologies being developed internationally that have the potential to be applied in New Zealand.

These include Carbon Capture and Storage (CCS), the process of capturing CO2 at source, (e.g. cement plant), transporting it to a storage site, and depositing it underground where it will not enter the atmosphere. 

Another new technology is Carbon Capture and Utilisation (CCU), which uses captured CO2 in the production of other materials, including concrete and concrete products.

An example is CarbonCure from Canada, which injects captured CO2 into fresh concrete at the plant. Once injected, the CO2 will find calcium and oxide particles and connect to form CaCO3 (limestone). This process replaces cement to around the level of 7%.

Conclusions

The concrete industry supports the climate change response (zero carbon) amendment bill in its aims to achieve a (net) zero carbon New Zealand by 2050.

Such commitment is based on a recent track record of significant emission reductions, and an understanding of the work required to nurture New Zealand’s Natural Capital under the Treasury’s Living Standards Framework.

However, in terms of clinker manufacture, there is only so much that can be done to reduce emissions with current technologies.

Fortunately, New Zealand has a number of decarbonisation options to explore, amongst which industrial SCMs and Natural (Class N) pozzolans will form a key component of the short-to-medium term solution.

Sustainability is not just about CO2 reduction. A holistic Life Cycle Assessment approach, which uses robust science and independent data, must be adopted in order to accurately assess a building’s impact across its entire life cycle.