Rick Henry: A concrete solution to a new Waitematā Harbour crossing

The New Zealand concrete industry managed an 11 per cent reduction in carbon emissions between 2005 and 2018 in New Zealand, despite increased volumes of concrete being used.. Photo / 123rf, File

OPINION

A low-carbon concrete second harbour crossing would showcase the commitment Auckland and New Zealand have to a more sustainable future, while providing the resilience and durability needed to maintain a critical transport connection.

Consider the resilience benefits that a low-carbon concrete tunnel would provide.

Let’s not forget one of the reasons an additional harbour crossing is required is that the current bridge is unlikely to achieve its intended design life. The slender steel structure of the clip-on lanes is too flexible, resulting in fatigue that requires constant maintenance and repair and limits the bridge’s adaptability to new uses.

The next Auckland harbour crossing must be able to withstand tornadoes, cyclones, extreme temperatures, earthquakes, tsunamis - everything that nature can throw at it – as well as trucks going off track.

Tunnels may well prove to be the best option when assessing all criteria, with the resulting construction emissions being justified by the whole-of-life benefits. Indeed, those emissions are already being mitigated.

Low-carbon cement alternatives are increasingly available and being used, while the concrete industry will soon release a roadmap to achieving net-zero carbon by 2050.

Things are already heading in the right direction with an 11 per cent reduction in emissions between 2005 and 2018 in New Zealand, despite increased volumes of concrete being used.

Further progress is under way. Holcim New Zealand has officially opened a new low-carbon cement replacement facility at the Ports of Auckland. Through this initiative, carbon emission savings will reach more than 75,000 tonnes a year, roughly equivalent to 3600 flights from Auckland to Christchurch, or removing 34,700 cars from the roads.

The Holcim cement dome on Quay St in Downtown Auckland. Photo / Supplied, File

Another large concrete provider, Fletcher Building, has announced a Concrete Innovation Laboratory in Christchurch, dedicated to finding more sustainable concrete solutions. This lab will complement the Fletcher Building-owned Golden Bay Cement works’ other efforts to reduce embodied carbon in concrete. The factory, near Whangārei, has been using up to three million old tyres a year as well as wood biomass from construction waste to substitute up to 50 per cent of coal use, without harmful effects from air discharges.

It’s not just industry players: academics in New Zealand, including my colleagues at the University of Auckland, are also working on ways to produce greener concrete. Progress like this is critical if concrete is to remain the material of choice in infrastructure in the face of looming need.

We currently have a massive infrastructure deficit, estimated at $210b by Treasury last year. The construction of the infrastructure needed to improve well-being and promote economic growth, however, faces multiple challenges.

Rick Henry. Photo / Supplied

Beyond the obvious issue of funding, we are constantly learning more about our exposure to natural hazards and the impacts of climate change.

Our infrastructure must provide resilient solutions that address the uncertainty of these perils, including housing and roading in Edgecumbe, Hawke’s Bay’s Esk Valley and flood-prone areas of Auckland. Much of the infrastructure required, including foundations, buildings, bridges, tunnels, and pipes, is made with concrete.

While there are other construction materials, the durability and versatility of concrete make it the go-to solution for many applications. Where would we be today without the construction of the massive concrete hydro dams essential for our much-lauded renewable power generation?

Much of what we know about concrete and its role in future resilience and reliability has come from recent research on concrete exposed to extreme environments including coastal infrastructure, wastewater pipes, and concrete structures exposed to earthquakes and structural fires.

We have learned that, in older concrete structures, the absorption of chlorides and CO2 can potentially cause corrosion of the reinforcement. The industry has responded by developing concrete mixes with incredible durability.

The fact that concrete absorbs CO2 has now been recognised by the UN IPCC as a benefit.

The performance of concrete buildings during the Canterbury earthquakes proved modern structural design could protect lives and allowed us to focus on designing more resilient buildings that are not damaged following major earthquakes.

We need to invest in infrastructure, and we need to do this with a long-term vision, standing on the shoulders of those researchers and companies committing time and money to finding new ways forward.

But we also need commitment from infrastructure providers and funders to use these new, low-carbon concrete alternatives. Concrete is an integral part of New Zealand’s infrastructure solution, and we should focus our attention on supporting the decarbonisation of the concrete industry.

- Associate Professor Rick Henry is the deputy head of the Department of Civil and Environmental Engineering at the University of Auckland.