Golden Bay Cement is New Zealand's only fully integrated cement manufacturing plant. Photo / Michael Cunningham
Construction is emission-intensive – whether it's a family home, a new event centre for the town or a wind turbine to generate renewable energy.
To meet Aotearoa's goal to half its greenhouse gas emissions by 2030, the construction industry with its manufacturers, engineers and developers will have to increasingly take climate change under consideration.
Developments in this sector become relevant for Northland when we're considering its booming population that has put the region on top of the list of New Zealand's fastest-growing region, and which is requiring a significant amount of construction.
Northland is also home to the country's only fully integrated cement manufacturing plant, Golden Bay Cement (GBC).
Being a fully integrated cement manufacturing plant means GBC is producing and then grinding clinker into the final cement products.
Clinker is an essential binding material in cement products.
"Cement production is an inherently carbon-intensive process," a GBC spokesperson explained.
Manufacturing accounts for 41 per cent of Northland's emissions.
"Clinker manufacture involves a chemical process to decarbonise limestone which requires heating it to around 870C, traditionally using fossil fuels to create the necessary process heat."
GBC has reduced fossil fuel use to less than 50 per cent and its electricity is about 85 per cent renewable.
This reduces their carbon dioxide emissions for clinker production to about 0.82 tonnes per tonne of clinker.
The manufacturer says its cement has about 20 per cent less CO2 emissions than New Zealand's primary cement importer.
GBC can produce up to 900,000 tonnes of cement clinker a year.
In 2019, New Zealand imported 124,474 tonnes, mostly from Thailand and Vietnam.
Modern cement plants that are not using renewable electricity and use fossil fuels typically emit 0.93 tonnes of CO2 per tonne of clinker, with older plants having higher emissions.
There have been efforts to reduce clinker content in cement using supplementary cementitious materials (SCMs).
Internationally, there has been a big move to using SCMs. Clinker content is down to 75 per cent in Europe.
GBC has reduced clinker content in cement from 96 per cent to 91 per cent and is working on reducing clinker content, however, "New Zealand's quality requirements make this challenging".
Northland's cement plant has reduced its emissions in other parts of the production chain, too.
GBC is reducing coal consumption, which fuels 45 per cent of its energy requirements, and titles itself "a world leader" in using biofuel with 30 per cent biofuel use at present and working to increase this.
Wood waste from internal recycling or reuse of any off-spec processed or raw materials covers another quarter of its energy consumption.
Earlier this year, GBC launched its tyre project – a new technology that combusts end-of-life tyres and combines its ash with cement, preventing up to 3 million used tyres going to landfill each year.
In 2008, the plant upgraded its air filtration technology reducing the dust emission, which is well below the consented limit, and their water reclaim system has reduced their need to bring in freshwater by about a third. Northland Regional Council regulates their water discharge requirements.
While GBC "is committed to meeting the science-based target for emission reduction with a 30 per cent reduction planned by 2030 and net-zero by 2050", the reduction target has to be financially viable.
"Reducing emissions adds cost. The Government's role is to maintain a level playing field with imports from countries that do not have the same requirements to reduce emissions," the spokesperson said.
"If a high-emission, low-cost product is able to be imported, it will simply drive production offshore and global net emissions will increase as a result."
In the short term, our local cement industry will be aspiring to lower clinker content in cement and increase biofuel.
For the long term, GBC is relying on carbon capture and storage technologies.
Scholars see another pathway in reducing greenhouse gas emissions – not necessarily within the manufacturing process but the embodied emissions of construction projects.
When tracing those greenhouse gas emissions, experts start with raw material extraction, transport and manufacturing.
They then consider emissions produced during the construction and the usage stage, and includes maintenance and repair processes.
Finally, the deconstruction with its disposal is taken into account completing the production line of emissions or embodied emissions, as often referred to.
While manufacturing is standardised in New Zealand, the building sector has few emission-related regulations compared with other nations like in Europe, Singapore or the US.
Our home insulation ratings, for example, are about half of what was required in the UK 20 years ago.
Dr Charles Clifton, associate professor of civil engineering at the University of Auckland, has worked nearly 40 years in steel construction and says to reduce embodied emissions we have to look at how we design and then use buildings.
"We need to focus in new buildings on minimising the cumulative embodied energy involved in building, operating and then decommissioning a given building.
"This involves using a mix of materials to achieve that end requirement, with each material used to its maximum advantage to achieve the end result," Clifton said.
Concrete, timber and steel are the three major materials used in construction. However, most buildings, especially those that use structural steel, are a mix of materials.
Tracing the embodied energy of the materials used is an important factor but shouldn't be the only decisive factor for the material choice of a new building.
Materials have to be understood and well incorporated in the structural design.
Clifton said many mistake timber as superior in terms of sustainability.
"One of the most widely stated inaccuracies is that timber is more sustainable than steel or concrete because a piece of timber absorbs CO2 in its final form in the building, while a piece of concrete or steel generates CO2."
"When [timber] is harvested and allowed to rot, it releases that carbon back as CO2.
"In managed forests, there are multiple rounds of pruning of the trees during growing, which require machinery and create waste that is allowed to rot.
"Then when the tree is harvested, the branches, roots and waste parts of the trunk are returned to the ground, which creates more CO2.
"The timber then has to be transported to mills, cut, kiln-dried, treated to make it durable, then dried again and less than half of the originally cut pieces of timber remain dimensionally stable enough at the end of that process to be incorporated into building framing.
"Other bits can be recycled into chipboard or plywood or other manufactured timber products, which have a high manufacturing component to them and hence high embodied energy.
"So, in general terms, structural timber has at best only a minor embodied CO2 advantage over structural steel or reinforced concrete."
Clifton also disputed claims by the national concrete industry that concrete is infinitely recyclable.
He said it could be crushed and used as aggregate in a range of roading and civil works, but it could not be put back into new concrete.
Meanwhile, steel manufacturing is emission-intensive, however, some 77 per cent of reinforcing steel and structural steel in New Zealand is recycled at the end of its working life.
"The focus should be on what generates the most energy-effective building over its lifetime, not focussing on whether steel-framed buildings are better than concrete-framed buildings or timber-framed buildings," Clifton summarised.
What experts can agree on, is that there is room to improve the environmental costs of our buildings – but it has to be understood as a holistic process.
The series
Friday: How to encourage climate action
Monday: Niwa scientists predict Northland's climate
Tuesday: How can we help?
Wednesday: What are our councils doing?
Yesterday: How we can fight for climate justice
Today: How to take industry into a sustainable future
Tomorrow: Regenerative farming and growing techniques
Monday: The future generation
Mercury's $287 million wind farm near Omamari will produce enough power for 27,000 homes.