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What if…we said ‘no’ to concrete?

Credit: Andy Carter

Concrete is magic. It gives form to the boldest civic ambitions and allows the wildest flights of architectural imagination; it can house millions or give expression to towering phallic capitalist hubris.

It’s also handy if you want to make a patio outside your back door.

The Romans used it (see the Colosseum), but the 20th century was when the world went concrete crazy – and it became synonymous with development and progress. It’s often confused with cement, the kiln-fired limestone-based substance that binds sand, aggregate (usually gravel or stones) and water to make concrete. The result is so incredibly strong and durable – especially when reinforced with steel – that it is today the second most widely used substance on the planet, after water.

Since 2003, China has poured more concrete every three years than the US managed in the entire 20th century. And thanks to its global Belt and Road programme of big dams, ports, roads, railways and cement factories across 50 countries, China will keep doing so.

Let’s pause there… and consider. Half of concrete’s CO2 emissions are created during the manufacture of cement; and as concrete hardens, it releases yet more CO2. ‘If the cement industry were a country, it would be the third largest carbon dioxide emitter in the world… surpassed only by China and the US,’ writes Jonathan Watts in The Guardian.

Concrete is thirsty – accounting for one-tenth of the world’s industrial water use. It makes strong storm defences – but concreted towns and cities trap floodwater. Its wind-borne dust causes silicosis and other respiratory diseases. It’s a dirty business. ‘Sand mafias’ operating illegally to supply the concrete industry terrorize local communities.

But given the power and ubiquity of concrete, isn’t giving it a miss just fanciful?

Luckily those developing alternatives don’t think so. Hempcrete is gaining traction as a viable construction material and alternative to standard concrete and clay bricks (which also emit CO2 in their manufacture). Made from a mix of hurd (a hemp by-product), lime binder and water, it is moulded into blocks and hardened in the open. Hemp grows fast and uses little land (10 tonnes can grow in 100 days on 0.4 hectares). Instead of emitting CO2, hempcrete actually absorbs it.

It weighs six times less than concrete, its makers say it can be made as strong, but you wouldn’t build a dam with it. It’s especially suitable for domestic construction and insulation, and being more flexible and fungus-resistant than concrete is better in earthquake-prone and humid regions.

Timber is also seeing a revival. Thanks to advances in construction systems, wooden eco-buildings are now reaching for the sky. Cross-laminated timber (CLT) was used to build the 14-storey Treet apartment block in Bergen, Norway. Hybrids of wood-and-steel and wood-and-concrete allow for more height. The HoHo building under construction in Vienna, will be 76 per cent wood in structure and 24 storeys high. According to woodskyscrapers.org, these advances ‘meet and exceed modern construction requirements including fire codes, building costs, construction times and structural requirements’.

Of course, to be eco-friendly all timber needs to be 100 per cent certified sustainable.

Benjamin Gill is a sustainable construction expert with social enterprises Bioregional and One Planet Living. He says: ‘We need construction to be a carbon sink rather than a source. That means scaling up an entire new supply chain and industry to deliver sustainably grown and sourced bio-based construction materials like FSC timber and hempcrete.’

Whether sustainable forestry practices are able to meet the demand if timber takes off as the primary building material remains to be seen. The shift would certainly incentivize us to value forests more. Other big mindset shifts might happen too. If something can only be built in concrete, should it be built at all? The higher and heavier you build, the bigger the carbon footprint, says Gill, so more human-scale construction could be beneficial in many ways. Concrete will still be needed for some things – securing wind-turbines, for example. But a wisely allocated concrete CO2 budget would rule out destructive (big dam) and vanity (the highest building) projects.

‘Concrete is one of the tools that allows humans to see themselves as separate from nature and our planet,’ says Gill. To move beyond it is ‘a huge opportunity to create a different construction industry that is carbon absorbing rather than emitting’.

Saying ‘no’ to concrete is a challenge, but it could be saying ‘yes’ to living with nature within planetary limits, to realism, to survival.

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