WATER NEW ZEALAND EMISSIONS REDUCTION
Low carbon concrete renaissance Concrete NZ chief executive Rob Gaimster says the sector’s 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. 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-oflife 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
We are 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 economy, employing over 7000 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 focusing 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
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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 the 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 cement Standard.
Alternative fuels
Considerable reductions in energy use (and therefore CO2 emissions) have been realised over the past decade by improving the efficiency of the cement kiln operation. 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 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
