Introduction

Introduction - NZ Concrete Industry Emissions Reduction

The New Zealand concrete industry is halfway towards meeting its target of a 30 percent reduction in carbon dioxide emissions by 2030.

ZERO CARBON ACT
Concrete NZ supports the Climate Change Response (Zero Carbon) Amendment Act, and its objective to ensure New Zealand plays its part in reducing Greenhouse Gas Emissions (GHG) under the Paris Agreement.

The Act gives New Zealand a clearly defined, long-term, emissions target, with an assured framework for managing the transition to a low-emissions future.

Long-term predictability in terms of policy direction is welcomed by the concrete industry, along with evidence-based decisions that deliver pragmatic emission reduction results.

MANAGED TRANSITION
Cement clinker manufacture is an inherently carbon intensive process, and cement companies are unable to reach zero carbon emissions with current technology. This is because the manufacturing process is primarily driven by the base chemical reaction resulting from the decarbonisation of limestone.

Cement manufacturing plants are capital intensive and typically operate on a twenty-year reinvestment/ upgrade cycle. Implementation of any new technologies or process changes will add significant business costs and would need to be part of a long–term investment plan.

Recommendations for a transition to a low emissions economy must therefore remain practical and achievable, be based on known and commercially viable technologies and processes, and account for raw material availability, supply chain dynamics and market demand for ‘quality’.

LOW CARBON MATERIAL
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 between 2005 and 2018 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 diverting / recycling waste streams, including returned concrete, away from landfill and into usable construction products.

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

SCMs are derived from lower embodied energy, industrial by-products or waste materials, and can result in environmental benefits, improved concrete performance, and long-term cost advantages. Typically, they are ground granulated blast furnace slag (waste from steel manufacture), fly ash (waste from coal combustion) or microsilica.

Volcanic ash (a natural pozzolan) from New Zealand’s North Island Volcanic Plateau is another type of SCM. The advantage of natural pozzolans is that there is a stable local supply, meaning they have the potential to be cost competitive.

New Zealand cement suppliers are currently investigating pozzolan blended cements with around 20-25 percent cement substitution. The New Zealand cement Standard (NZS 3122) allows for up to 35 percent replacement with fly-ash or pozzolans, up to 75 percent with ground granulated blast furnace slag, and 10 percent with microsilica.

Image: Portland Cement Association (PCA)

ALTERNATIVE KILN 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, a significant energy user.

New Zealand’s only integrated 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 is substituted with wood waste.
Fossil fuel substitution with waste vehicle tyres will begin shortly

The environmental benefits of using alternative fuels in cement manufacture are:

the need to use non-renewable fossil fuels such as coal is reduced; and
the recovery of energy from waste is maximised, methane emissions reduced, and landfill space optimised.