Reinventing basic materials
This is a part of the Concrete, steel and timber feature
World-class research, award-winning designs and a new mindset are all helping New Zealand manufacturers, architects and designers take a fresh approach to those most fundamental of building materials – concrete, steel and timber.
WHEN IT’S NOT done carefully, the selection of concrete, steel or timber for a new building can seem like a scaled-up version of rock, paper, scissors – an instinctive choice based on personal preferences, what’s worked in the past and the desire to make an instant impact. Too often, there is too little consideration for the long-term performance of a building and what will eventually happen to the materials in it.
Material choices are changing
Going up more than 3 storeys? The obvious choice is concrete or steel. Worried about the carbon footprint? You need timber. That’s been a relatively common way of thinking, but the world is changing so fast that it’s already outdated.
Engineered timber is now playing a key role in ever-taller buildings, and the carbon footprints of concrete and steel are shrinking. Fossil-free steel has been produced. The Global Cement and Concrete Association – representing 80% of the global cement industry excluding China – has committed to producing carbon-neutral concrete by 2050, a move fully supported by Concrete NZ and the New Zealand concrete industry.
Thinking about the circular economy
While there are extraordinary changes taking place in the manufacture and use of each of the three materials, an equally important change is in the overall mindset behind their use. It is no longer a matter of choosing either/or but of looking at what materials are the best match for particular needs and, above all, taking the longer-term view that is summed up in the idea of a circular economy.
A one-way, linear economy starts off with extracting raw materials and ends up with demolition waste filling landfills, but a circular economy designs out waste and keeps materials in use. Products are designed for a long life and are able to be repaired and eventually disassembled and reused or recycled. The process is fuelled by renewable energy. The benefits range from reduced waste and greenhouse gas emissions to long-term cost savings.
Jonas Bengtsson, CEO and co-founder of Edge Environment in Australia, specialising in sustainability, points out that planning for adaptive reuse is becoming one of the most impactful strategies, such as behind a new car parking building. The building’s owner could have built a structure with low floor heights that could only ever be used as a car park. Instead, they allowed the possibility for the building to be converted to offices or apartments in a few decades’ time by designing higher floor heights from the beginning.
Another example that can be applied to any building is designing for maintenance – designing a structure that will have a long service life thanks to the ease of maintenance.
The whole concept of a circular economy is informed by life cycle assessment (LCA) – calculating the potential environmental impacts of materials, products and services across their life cycle.
One of the key findings of LCA is that both embodied and operational carbon emissions make significant contributions to a building’s greenhouse gas emissions over its service life.
Results show that a large proportion of embodied emissions occur from building product manufacturing, transport and construction before a house is occupied (Figure 1). In fact, these emissions can be the highest of any yearly emissions during the building life cycle.
While these emissions may be lower overall than operational emissions (from energy and water use), the operational emissions occur incrementally over many decades.
In terms of whole-of-life embodied emissions, some of the main contributors by material we see are carpets, sheet metal roofing and concrete.
If concrete brings to mind strength and durability, it’s with good reason. Concrete sea walls built by the Romans 2,000 years ago are still fit for purpose. The magnificent 1,900-year-old Pantheon in Rome is still the largest unreinforced concrete dome in the world.
Concrete is also at the forefront of new construction technologies such as 3D printed buildings.
For all its substantial benefits, concrete currently has a comparatively big carbon footprint, largely from the production of Portland cement. This cement is made by heating limestone and other ingredients at very high temperatures – a process that results in large volumes of carbon dioxide emissions from the fossil fuels used and the heated limestone itself.
The New Zealand concrete industry is making significant improvements, however:
- Emissions from Portland cement production/consumption reduced by 15% between 2005 and 2018 from the use of alternative kiln fuels and a lift in manufacturing efficiency. That’s impressive when you consider that concrete production increased by 13% during the same period.
- The industry is targeting another 15% drop by 2030. Some will come from reducing waste and lifting recycling. A real gain is anticipated from replacing some Portland cement in concrete mixes with low-carbon supplementary cementitious materials (SCMs) – byproducts from heavy industry such as fly ash or slag or natural materials such as volcanic ash (see SCMs reduce concrete emissions for more).
Developing a roadmap
Rob Gamister of Concrete NZ says that the organisation is currently collaborating with its members to develop a roadmap tailored for New Zealand with a similar framework to that adopted by the Global Cement and Concrete Association. The roadmap will set milestones on the path towards net-zero carbon concrete by 2050, with actions needed:
- Increased use of SCMs – recycled and natural.
- Efficient energy sources for manufacturing and delivery.
- Driving waste minimisation in manufacturing, delivery and construction.
- Using recycling processes to minimise the use of virgin materials.
- Adopting appropriate new technologies – for example, carbon capture and utilisation.
- Engaging with local communities.
The New Zealand concrete industry is very excited about the growth in uptake of natural SCMs – pozzolanic volcanic ash from New Zealand’s North Island volcanic plateau. The domestic supply of natural SCMs is currently being commercialised through a programme of mix design research. Once complete, this will enable strong market demand for low-carbon concrete to be met.
Given the range of concrete mixes available today, it is no longer enough for engineers, architects and designers to specify concrete just on the traditional factors of strength, slump and so on.
Steel production in Aotearoa is a good example of a circular economy – 85% of our building and construction steel waste is recycled.
Rick Osborne, Chief Executive of Metals New Zealand, points to improvements under way in the domestic steel industry:
- New Zealand Steel worked with its supplier of co-generated electricity, Alinta Energy, to lift on-site electricity generation at Glenbrook by almost 10% – 5% of total electricity requirements.
- Fletcher Steel has received funding to decarbonise its coil coating process. This will reduce fossil fuel consumption by up to 89% and eCO2 emissions by 67%.
- Steel & Tube’s greenhouse gas emissions are down 9% year on year through a range of initiatives.
Even more exciting is the prospect being explored at Victoria University of Wellington for replacing coal with hydrogen as the fuel behind steelmaking. The hydrogen can be produced from water using renewable energy such as wind power.
Victoria’s Robinson Research Institute has demonstrated the process using hydrogen and New Zealand iron sand at temperatures up to 1,000°C to produce very high-purity iron. The key benefit is that this process releases water vapour, not carbon dioxide.
The team has received $6.5 million from MBIE’s Endeavour Fund for research into the scale-up of hydrogen steelmaking in New Zealand. (In Sweden, a venture formed by steel, car and mining companies and supported by two universities, the Swedish Government and the European Union has already produced its first fossil-free steel. Fossil-free steel is earmarked for building Volvo cars.)
Timber, including engineered timber, is a very carbon-friendly building material thanks to trees absorbing carbon dioxide from the atmosphere as they grow. Where timber is used on a building, it typically helps reduce its carbon footprint.
LVL (laminated veneer lumber) is the key component in Te Whare Nui o Tuteata, the new Rotorua headquarters and innovation hub for Crown research institute Scion. The building has won multiple national and international awards for its design. The architects have said that the building achieved embodied carbon zero when it was completed.
Advances in timber technology
Timber buildings have traditionally been limited in size and come with particular fire risks, but both of those limits are changing, with engineered timber behind some big advances. The weight of timber is only onefifth that of concrete, but engineered timber has similar compressive strength as concrete.
Research at Canterbury University, funded by the Earthquake Commission, has found that multi-storey walls constructed from cross-laminated timber (CLT) can be strong and resilient in earthquakes. The research team designed high-capacity connections for the walls. They found that steel dowels in the connections bent to absorb energy and prevent the walls from being significantly damaged or collapsing. After an earthquake, the dowels could just be replaced and building occupants could quickly return.
Innovations are continuing. Professors and students at the University of Auckland and AUT developed the Tectonus earthquake protection devices. This New Zealand initiative is being picked up around the world.
In Australia, Building 4.0 CRC, an industry-led research initiative co-funded by the Australian Government, is looking into a low-carbon suspended floor system capable of spanning 8 m or more. The idea is to enable large-scale application in multi-storey mass timber projects.
There are a growing number of resources available to help engineers, architects and designers in their material selection, including environmental product declarations (EPDs) published by manufacturers about their products and BRANZ carbon tools.
EPDs are independently verified public statements of the environmental performance of materials or products. They allow comparison of products based on their environmental impacts. Not all manufacturers publish EPDs, but the number is growing rapidly. In New Zealand, this is partly because government agencies such as Kāinga Ora now have specific requirements around greenhouse gas emissions and environmental impacts in their work with construction companies.
BRANZ has also recently released a series of new online carbon tools that can help. The suite of tools now available on the BRANZ website is made up of three carbon foot-printing tools and two life cycle assessment tools:
- CO2NSTRUCT is a database of embodied carbon and energy figures for building materials and products.
- CO2RE covers greenhouse gas emissions for residential wall, floor and roof constructions (expressed as per m² of the building element). It allows evaluation based on construction R-value and whole-of-life embodied carbon.
- CO2MPARE is a database of calculated greenhouse gas emissions for a set of reference residential and office buildings. It also contains carbon budgets for those buildings. It can be used for benchmarking and target setting.
- LCAQuick calculates environmental impacts of any building designs, with a focus on residential and office typologies.
- LCAPlay is a concept-level exploratory LCA tool for commercial buildings.
The BRANZ tools are available at www.branz.co.nz/calculators-tools/.
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Articles are correct at the time of publication but may have since become outdated.