Decarbonising concrete: New Zealand's challenge and opportunity

Decarbonising concrete

As a fundamental material for building a modern society concrete remains indispensable and plays a pivotal role in infrastructure decarbonisation. Tim Kleier, sustainability and policy director for Concrete NZ was invited to talk about the strides the concrete industry is taking in the quest for decarbonisation.

In the quest for infrastructure decarbonisation, concrete plays a pivotal role. As a fundamental material for building a modern society - supporting our transport infrastructure, hospitals, schools, and more - concrete remains indispensable. However, the challenge lies in decarbonising this essential material.

Concrete NZ is a member-based association that includes all the cement and ready-mix concrete suppliers across the country, as well as concrete precasters, masonry producers and steel reinforcement processors. One of its focusses is on improving the sustainability credentials of the industry. This includes reducing the carbon footprint of concrete, a material composed of natural ingredients like coarse aggregate, sand, water, and cement. Despite its simple composition, cement accounts for over 80% of concrete’s global warming potential in large parts due to the CO₂ released during its production from limestone.

Even today, low-carbon concrete mixes are available, capable of reducing embodied carbon emissions by 30-40% at little to no additional cost. To perpetuate these gains, it is essential to specify performance-based CO₂ reduction targets rather than prescriptive material requirements when engaging suppliers. This allows suppliers to optimise mixes based on available materials and project conditions.

Decarbonising concrete is a multifaceted challenge that requires innovation, collaboration, and commitment across the industry. By leveraging new technologies, improving efficiency, and adopting sustainable practices, we can significantly reduce the carbon footprint of concrete and contribute to a more sustainable future.

Key strategies for decarbonisation

Fuel replacement:

The production of clinker, a key component of cement, requires significant heat. While much of this heat is already generated from waste materials, further replacing fossil fuels with renewable energy sources can reduce emissions.
Supplementary cementitious materials (SCMs):

SCMs, such as slag and fly ash, can partially replace cement in concrete mixes, reducing the overall carbon footprint. Although New Zealand has been slow to adopt SCMs due to a lack of domestic industrial by-products, recent investments have increased their availability. Additionally, natural SCMs like pozzolans from volcanic ash offer further potential.
Design and construction:

While New Zealand’s seismic activity limits some design flexibility, improving the efficiency of concrete use remains crucial. Globally, concrete accounts for 6-7% of man-made carbon emissions, but in New Zealand, it is only 2%, indicating relatively efficient use.
Production efficiency:

Enhancing the efficiency of concrete mixes, production and delivery can also contribute to decarbonisation. This includes using electric or hybrid trucks and centralising mixing operations to reduce diesel use.
Carbon uptake:

Concrete naturally absorbs CO₂ from the atmosphere over time, incorporating it into its structure. Recognising and accounting for this process can help offset emissions, although it is a slow process and not a short-term solution.