Chief Executive's Upfront
Low Carbon Concrete Renaissance

The concrete industry is in the midst of a fervent period of progress, as recent achievements in emissions reduction are set to continue via manufacturing and delivery initiatives that will drive the industry towards net zero carbon concrete by 2050.

Rob Gaimster, Chief Executive

After water, concrete is the most widely used substance on Earth. In many developed countries, concrete infrastructure comprises about 60 percent of the built environment.

Concrete has shaped civilizations from as far back as the Roman Empire. Today it is indispensable in the development of residential and commercial construction, as well as infrastructure development, including water management systems.

As a metaphor for strength, concrete is renowned for its whole-of-life benefits, offering significant sustainability benefits based around its inherent properties of durability, thermal mass, recyclability, CO₂ uptake, resilience to extreme weather and hazards, as well as its local availability.

NEW ZEALAND CONCRETE
New Zealand is virtually self-sufficient in concrete, and the associated materials required for its production. Along with the fact that ready mixed concrete is produced within close proximity to where it is cast, this means that concrete easily meets the sustainable development principle of products being consumed near the place of origin.

The concrete industry plays a key part in the New Zealand economy, employing over 7,000 people across 190 concrete plants and 22 cement manufacturing and distribution facilities throughout the country.

Record levels of quality assured concrete (4 million cubic metres annually) are currently being produced using locally sourced aggregates, recycled water and either locally manufactured or imported cement.

EMISSIONS REDUCTION
Committed to playing a proactive role in helping New Zealand achieve its Climate Change Response (Zero Carbon) Amendment Act 2019 objectives, the concrete industry is halfway towards meeting its target of at least 30 percent reduction in CO₂ emissions by 2030.

Independent sustainability consultants - thinkstep - confirm that emissions from cement have been reduced by 15 percent between 2005 and 2018.

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

The 15 percent reduction in emissions was achieved through 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.

In addition to focussing on CO₂ generating processes, the wider industry has also worked to enhance its environmental practices by adopting synthetic fuels for its vehicle fleet, as well as diverting/recycling waste streams, including returned concrete, away from landfill and into usable construction products.

SUPPLEMENTARY CEMENTITIOUS MATERIALS (SCMS)
The increasing global use of low carbon SCMs to partially replace Portland cement and therefore directly reduce embodied CO₂ makes sound ecological sense.

SCMs are derived from lower embodied energy, recycled materials, and can result in environmental benefits, improved concrete performance, and long-term cost advantages.

Typically they are ground granulated blast furnace slag (from steel manufacture), fly ash (from coal combustion) or microsilica. Volcanic ash (a natural pozzolan) from New Zealand’s North Island Volcanic Plateau is another type of SCM.

To remove barriers to the increased uptake of SCMs, Concrete NZ has recently completed a Building Research Levy funded project to assess classification techniques along with the fresh and hardened performance of SCM concrete, outputs from which will feed into a review of the New Zealand cement Standard.

ALTERNATIVE FUELS
Considerable reductions in energy use (and therefore CO₂ emissions) have been realised in New Zealand over the past decade by improving the efficiency of the cement kiln operation.

New Zealand’s end-to-end cement manufacturer, Golden Bay Cement, uses alternative waste fuels for a substantial part of its operations and is continually examining the practicalities of increased supplementation.

A significant proportion of fossil fuel used at its Northland facility has been substituted with wood waste (biofuel). More recently an initiative to use up to 50 percent of the 6.3 million waste tyres created in New Zealand each year will reduce coal use by 15 percent, resulting in a reduction in CO₂ emissions of around 13,000 tonnes annually.

The environmental benefits of using alternative fuels in cement manufacture are not just that the need to use non-renewable fossil fuels such as coal is reduced; but also the recovery of energy from waste is maximised, methane emissions reduced, and landfill space optimised.

CARBON CAPTURE
In addition to SCMs and alternative kiln fuel, an emerging technology being adopted in New Zealand to help realise net carbon zero concrete is Carbon Capture and Utilization (CCU).

This process, which can reduce the carbon footprint of concrete by an average of 15 kilograms per cubic metre, takes captured CO₂ from local oil refineries, purifies and transports it to the concrete plant, where it is stored in a pressurised tank.

A precise dosage of CO₂ is injected into the wet concrete during mixing, which then reacts with the cement’s calcium ions to form calcium carbonate. This is embedded in the concrete, increasing its strength while eliminating the CO₂.

WATER & CONCRETE
Within a broader sustainability context, there are many opportunities where concrete systems can be used to improve water control, in particular stormwater, to protect waterways from pollution and safeguard groundwater recharge and aquifer supplies.

The use of pervious concrete or permeable concrete paving can play an important role in an overarching management strategy to mitigate the environmental impacts of stormwater.

These sustainable urban drainage systems allow rainwater to filter through the paved surface in a controlled way into the ground before being released into sewers or waterways. Mimicking natural drainage regimes and improving visual and amenity forms, their applications can be as diverse as drives, paths, general landscaping or other hard surfaces.

Combined with the robustness and flexibility of traditional concrete pipes, the uptake of these new systems will see concrete-based water management solutions play a critical role in realising future infrastructure development.

FUTURE GOALS
Under the Concrete NZ banner the concrete industry has developed a medium-term vision which states that by 2030 the concrete industry will be recognised as a sustainable, socially responsible and profitable participant in the construction sector, and have reduced its global warming potential by at least 30 percent of 2005 levels to benefit the well-being of future generations, by:

• Supplementary cementitious materials (SCMs)
• Efficient energy sources for manufacturing and delivery processes
• Driving waste minimisation in manufacturing, delivery and construction
• Using recycling processes to minimise the use of virgin materials
• Adopting new technologies where appropriate
• Being engaged with our local communities

Beyond 2030, the New Zealand concrete industry is targeting net zero carbon by 2050.

Concrete NZ is currently collaborating with its members to develop a 2050 Cement and Concrete Industry Roadmap for Net Zero Carbon Concrete to define the industry’s commitment to producing carbon neutral concrete by 2050, in line with global climate targets.

The Roadmap’s framework - Past, Present and Future actions – will set out in detail how in collaboration with built environment stakeholders and policymakers, including water concerns, the concrete industry will fully decarbonise.

Taken from Water journal March/April 2022 Issue 223.