Within the complicated paradox of building concrete walls

Japanese authorities, wanting to better protect communities in the future, opted to build larger defenses. Concrete walls that stretch over 400 km and almost reach 15 meters high In places, they now line the coast to withstand incoming waves and give residents enough time to evacuate in the event of another tsunami.

They were recently tested by a 7.4 magnitude earthquake that struck off the coast of Fukushima Prefecture on March 16, 2022. killed at least four people and hurt many more. Luckily, the resulting tsunami was negligible compared to that of 11 years ago.

These dikes will also serve as a line of defense against the effects of climate change. A recent report The Intergovernmental Panel on Climate Change found that even in the best-case scenario, if global warming stops at 1.5°C, sea levels could rise 0.55 meters on a global average by 2100. This could lead to debilitating storm surges in many places.

Paradoxically, these walls, which are intended to protect people from the consequences of global warming, also contribute to this. We have estimated the emissions associated with the construction of the concrete breakwaters in northeastern Japan to be around six million tons of CO₂ by considering their size, length and use industry tools.

A reinforced seawall in northeastern Japan built after the 2011 tsunami. [Photo:Ravindra Jayaratne/courtesy of the authors]

So how can countries build stronger levees without worsening climate change? After studying damaged breakwaters in southern Sri Lanka (2004) and north-eastern Japan (2011) after the tsunami with colleagues from Waseda University, and considering the University of East London’s low-carbon concrete research, we may have found an answer.

Low carbon concrete

Concrete is the most commonly used material for making breakwaters. Cement, the main binder in a concrete mix, consists primarily of clinker – a residue produced when limestone and clay are calcined in a kiln heated to 14,500°C. To generate that much heat, fossil fuels are usually burned, releasing greenhouse gases.

Cement production is responsible for approx 7% of annual CO₂ emissions. But without concrete, many of the world’s most impressive buildings and structures – such as the Australian Opera House in Sydney and the Hoover Dam in Las Vegas – would not exist. One of the biggest challenges for the construction sector is reducing the carbon footprint of concrete while maintaining the Services a cheap and durable building material.

One way to achieve this is to replace cement with recycled industrial waste such as granulated slag from steel mills and pulverized ash from coal-fired power plants (essentially the residue that can be scraped from the bottom of blast furnaces).

Our newly designed low-carbon concrete mixes Use these two recycled materials. In fact, it was possible to use up to 60% steel furnace scrap in the mixes without the concrete losing its compressive strength, which is critical to the structure’s load-bearing capacity. The resulting mixes had a 40% smaller carbon footprint than traditional concrete.

Our designs Also use steel fibers, which resemble hairpins, which can be added to the concrete mix, eliminating the need to assemble giant steel grids. This reduces the cost and emissions of construction and the end product is just as strong as a traditional breakwater.

Working with nature

Concrete breakwaters can even promote biodiversity. Some are structured so that they mimic reef habitatswhich encourage the settlement and growth of marine plants and animals in their grooves and protruding surfaces.

This concrete replicates the shape and texture of coral and other reef species. [Photo: Sensicon/courtesy of the authors]

Even the best breakwaters break over time. Miraculously, engineers have developed self-healing concrete that uses Microorganisms that can produce limestone to repair these structures autonomously. The idea of ​​living organisms weaving through and repairing concrete, a material normally thought of as cold and lifeless, is very exciting to us.

In the future there will likely be even more sustainable concrete designs as 3D printing allows us to create more efficient patterns that use less material and produce less waste.

Using less to build more can be disconcerting coastal communities who live in fear of tsunamis, as sustainable breakwaters are likely to be thinner, smaller, and curved rather than straight. But these structures are just as strong and show that the world can adapt to the effects of climate change without making it worse.

Ravindra Jayaratne is a lecturer in coastal engineering at the University of East London and Ali Abbas is Associate Professor of Civil Engineering at the University of East London. This article is republished by The conversation under a Creative Commons license. read this original article. Within the complicated paradox of building concrete walls


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