The world’s growing Concrete Coasts

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The world's growing concrete coasts

The world’s coastlines are turning to concrete, at a huge cost to wildlife and the climate. But new technologies may offer a way to shore up coasts while benefiting biodiversity.

It’s one of the most impressive feats in modern engineering, and crossing the world’s longest sea bridge – the 55km (34 miles) Hong Kong-Zhuhai-Macau bridge, which opened in October 2018 at a cost of $20bn (£15.9bn) – certainly has its benefits. But impressive as it appears, this mammoth construction project, like so many others, has come at a cost.

No less than one million tonnes of concrete were used in the eight years it took to build the bridge. It was this concrete that invaded the habitat of the critically endangered pink dolphin, and is thought to be the reason that dead dolphins washed up on nearby shores while the population near the bridge plummeted by 60%. Of course, dolphins weren’t the only victims – habitats are destroyed and countless other marine species are affected when large amounts of concrete are poured into the ocean.

Destruction of this kind is often the cost of using concrete – the most widely used manmade material on Earth. With three tonnes per year used for every person in the world, there are few parts of the planet that concrete hasn’t reached. The production of concrete is also a huge emitter of CO2. At least 8% of humanity’s carbon footprint comes from the concrete industry, mostly from the production of cement – one of concrete’s principal components. The cement industry generates around 2.8 billion tonnes of CO2 per year – more than any country other than China or the US.

In the oceans, concrete is the main construction material, accounting for more than 70% of coastal and marine infrastructure such as ports, coastal defence structures and waterfronts. In China, for example, around 60% of its coast is effectively concrete. Similarly, more than 14,000 miles of the US’s coastline is covered in concrete.

In China, around 60% of its coast is effectively concrete. Similarly, more than 14,000 miles of the US’s coastline is covered in concrete

“Concrete is damaging in the ocean because, to put it in place, natural ecosystems are destroyed,” says Alex Rogers, director of science at REV Ocean, a not-for-profit company studying ocean health and raising awareness of global impacts on the marine environment. “Concrete is a conventional material, everyone understands it, and it is low cost. But really, in this day and age, when we’re looking at much more sustainable ways of carrying out development – whether it’s coastal reclamation or other forms of building – we should be looking at alternative materials that have a lower impact on the environment.”

By retrofitting concrete surfaces with eco-tiles and panels that are designed with greater surface complexity, it gives room for marine life to colonise.

Natural habitats such as saltmarshes are an effective protection from the sea, and support a wide range of species (Credit: Alamy)

The bio-blocks are designed to mimic the intertidal zone – the area where the sea meets the land at high and low tides – in a bid to provide a more suitable habitat for marine species

A 15-metre (49ft) installation has already been set up as a test site for the eco-shoreline that will eventually stretch 3.8km (2.4 miles), and is expected to be completed by 2023. The bio-blocks are designed to mimic the intertidal zone – the area where the sea meets the land at high and low tides – in a bid to provide a more suitable habitat for marine species.

Wildlife-friendly blocks could reduce the harm to marine life by land reclamation (Credit: ECOncrete)

Furthermore, unlike traditional concrete, which is highly alkaline, the specially designed concrete that is used for fabricating bio-blocks has a pH value (a measure of the acidity of substances) near to that of sea water, which helps to promote the growth of intertidal marine species such as crabs, molluscs, clams, mussels and oysters. The relatively neutral pH value of the bio-blocks is attained by replacing some of the ordinary Portland cement used in conventional concrete with alternative cementitious materials, such as slag cement, which has a secondary benefit of producing lower CO2 emissions.

“The seawater pH level is around 8, which is suitable to most marine organisms,” says Leung. “However, normal concrete has a pH of 12-13 which is not favourable to the colonisation of marine life. Therefore, concrete-based eco-engineered bio-blocks are commonly made with lower surface pH (pH 9 to 10) that are more suitable for marine organisms.” 

ECOncrete’s products are already in use across eight countries and six different seas, from seawalls in Hong Kong to the Port of Rotterdam. “Our vision is that in the future, all man-made structures in coastal and marine environments will be designed and built with environmentally sensitive technologies,” says Perkol-Finkel.

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