By: Dr. Jacqueline Balston, Director of Sustainability, IPWEA.
The problem with concrete
In 2020 the global production of cement was 4.1 billion tonnes – up from 1.4 billion tonnes in 19951. When mixed with sand and water, the resulting concrete is estimated to be enough to cover the whole of England every year2. Concrete is now the most commonly used material on earth after water2.
The process of producing concrete is responsible for an estimated 2.8 billion tonnes of CO2 each year2 or about 8% of global greenhouse gas emissions3. If it were a country, concrete would be the third largest emitter in the world after China and the USA. Most contributions come from the production of cement that uses coal, gas or electricity to generate the heat needed to convert calcium carbonate (limestone) into calcium oxide (lime). The chemical reaction also produces CO2 as a by product4.
Because of its hard wearing, long-lived qualities, concrete is a popular choice for construction and infrastructure projects – and yet, if we are to meet the Paris agreement on climate change, annual carbon emissions from the cement industry need to fall by at least 16% by 20302 as a first step to reducing our collective carbon emissions to zero by mid-century.
However, alternative materials such as steel, asphalt and plasterboard are currently more energy intensive than concrete. And the world’s forests are already diminishing rapidly without a surge in extra demand for timber2. So it seems that concrete has to change
However, alternative materials such as steel, asphalt and plasterboard are currently more energy intensive than concrete. And the world’s forests are already diminishing rapidly without a surge in extra demand for timber2. So it seems that concrete has to change.
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Maintenance of existing stock
The most sustainable option available to asset managers is to extend the useful life of existing concrete structures by improving maintenance, refurbishing old stock and protecting assets from changes in the climate.
In 2019 IPWEA released Practice Note 12.1: Climate change impacts on the useful life of infrastructure. The guide describes the likely impacts of climate change on infrastructure including accelerated carbonation, expansion and cracking of concrete. A simple decision tree methodology for determining the likely change to asset useful life is provided and estimates of useful life for over 200 assets is given5.
A follow-up publication Practice Note 12.2: Climate Resilient Materials for Infrastructure Assets released in 2021 provides an extensive range of options to reduce the impact of climate change and extend asset useful life6. Options include changes to maintenance schedules, application of protective coatings, strengthening existing members or altering the position of vulnerable asset components5,6.
Reuse and upcycling concrete assets
In many cases the long lifespan of concrete (50-100 years depending on mix specification and use) means a concrete structure will often outlast the design life of the asset and there is the opportunity to refurbish or repurpose the structure. There are many examples of warehouses, agricultural buildings, factories, town halls and even silos that have been converted into sports facilities, offices, shops or housing. Even infrastructure such as freeways and bridges can be repurposed for use by cyclists and pedestrians or even urban greening and farming projects.
Recycling concrete
Currently most demolished concrete goes to landfill sites or is crushed and reused as aggregate, but there are numerous opportunities to reuse the material. Slabs can be cut and used as pavers, turned into outdoor seating or used in gabion walls.
Due to quality control and testing requirements, it is difficult for recycled crushed concrete to be used as an aggregate in high specification concrete mixes (e.g. for structural applications). However, crushed concrete can be reused in lower specification products such as road base materials6. Other waste supplementary cementitious materials such as fly ash and ground granulated blast slag can also be used to reduce the amount of Portland cement used in a concrete mix6.
Alternatives to concrete
When there is a perceived need for a new concrete asset, the first question for the asset manager to ask is whether the asset is really needed at all? And if so, whether there is an alternative that will do the job. For example, numerous studies show that widening and extending freeway infrastructure only increases traffic congestion because of behavioural changes by motorists7. More sustainable alternatives include increases to public transport capacity8, cycle paths, improved digital networks and the decentralisation and rejuvenation of regional towns.
In some cases, green infrastructure can do a better job than hard concrete structures. One example is the use of mangroves and other coastal vegetation to reduce erosion and storm surge in place of sea walls9. The benefits of these “soft” solutions in the coastal zone is that they can migrate inshore with sea level rise over the coming decades, provide habitat for other species and green spaces for recreation.
Alternative materials may also be a better option than concrete and include cross laminated timber from certified sustainably-managed forests. The high-rise timber office building “25 King” in Brisbane is a great example of inner city options with a lower carbon footprint compared to concrete counterparts and effectively acts as a carbon sink by preserving the wood within the building10.
Climate smart concrete
When no other option but new concrete remains, smart design and detailing (considering the specific location, climate conditions and application), good workmanship and quality concrete mixes are likely to be the most effective way of achieving sustainable and resilient concrete structures that last for a long time6. Modifications to cement and concrete production can yield reductions in water content, carbon and energy input4. Inclusion of industrial waste by-products such as fly ash is now locally available in NSW6. Different mixes can reduce the carbon footprint of a binder by up to two-thirds6.
Low carbon and carbon neutral concrete is also now available on the market in Australia6. These concretes use renewable energy in the process of manufacturing cement rather than fossil fuels and may have bi-product CO2 and other emissions offset.
Finally, designing concrete assets for future flexibility and alternative uses could enable a concrete structure to outlast the initial use case while utilising the durability of the material6. And maintaining clear records of materials used in the mix may aid future recyclability6.
For further information please access a copy of Practice Notes 12.1 and 12.2 on the IPWEA website at: www.ipwea.org/pn12-2
References
1. Statistica (2022), Cement production worldwide from 1995 to 2020, Accessed 31 Jan 2022 at https://www.statista.com/statistics/219343/cement-production-worldwide/
2. Watts, J. (2019), Concrete: the most destructive material on Earth. The Guardian. Accessed 31 Jan 2022 at https://www.theguardian.com/cities/2019/feb/25/concrete-the-most-destructive-material-on-earth
3. Rodgers, L. (2018), Climate change: the massive CO2 emitter you may not know about. BBC News. Accessed 31 Jan 2022 at https://www.bbc.com/news/science-environment-46455844
4. Miller, S.A., Horvath, A.; Monteiro, P.J.M. (2016), Readily implementable techniques can cut annual CO2 emissions from the production of concrete by over 20%. Environmental Research Letters, Volume 11, Number 7. https://iopscience.iop.org/article/10.1088/1748-9326/11/7/074029/meta
5. IPWEA (2019), Practice Note 12.1: Climate change impacts on the useful life of infrastructure. Institute of Public Works Engineering Australasia, Sydney, Australia. Accessed 5 February 2022 at https://www.ipwea.org/publications/ipweabookshop/pn12-1
6. IPWEA (2021), Practice Note 12.2: Climate Resilient Materials for Infrastructure Assets. Institute of Public Works Engineering Australasia, Sydney, Australia. Accessed 5 February 2022 at https://www.ipwea.org/publications/ipweabookshop/pn12-2
7. Duranton, Gilles, and Matthew A. Turner. 2011. “The Fundamental Law of Road Congestion: Evidence from US Cities.” American Economic Review, 101 (6): 2616-52. Accessed 5 February 2022 at https://www.aeaweb.org/articles?id=10.1257/aer.101.6.2616
8. Buchanan, M. The benefits of public transport. Nat. Phys. 15, 876 (2019). https://doi.org/10.1038/s41567-019-0656-8 Accessed 5 February 2022 at https://www.nature.com/articles/s41567-019-0656-8#citeas
9. Spalding M, McIvor A, Tonneijck FH, Tol S and van Eijk P (2014), Mangroves for coastal defence. Guidelines for coastal managers & policy makers. Published by Wetlands International and The Nature Conservancy. 42 Accessed 5 February at https://www.nature.org/media/oceansandcoasts/mangroves-for-coastal-defence.pdf
10. Aurecon (2022), 25 King, Brisbane Australia. Aurecon Projects. Accessed 5 February 2022 at https://www.aurecongroup.com/projects/property/25-king
