5 Concrete
We live in a world of concrete. After water, it’s the most widely used substance on our planet, and its usage around the world, ton for ton, is twice that of steel, wood, plastics and aluminium combined.
Its invention in 1824, by a bricklayer in Leeds who first produced the Portland cement used to bind the aggregates used in concrete, quite literally paved the way for the creation of the modern world, enabling humans to mould high-strength, stone-like structures of almost any shape.
Concrete’s ubiquity comes at a high price though: if the cement industry were a country, it would be the third-largest emitter of carbon dioxide in the world, after the US and China, as it releases over 2.8 billion tonnes into the atmosphere each year.
A 2018 report suggested concrete contributes up to 8 per cent of the world’s CO2 emissions.
It also requires phenomenal amounts of water, sucking up around a tenth of all water used in industry – often in areas with critical water shortages.
Major construction firms team up to get the carbon out of concrete
Canary Media
Engineers and architects can reduce the proportion of cement in a number of ways. One is to use higher-quality aggregate that imparts more structural integrity to the concrete that’s made with it.
Another is by using what’s called “supplementary cementitious materials” to replace a portion of the cement used in different mixes of concrete. Fly ash from coal plants and slag from steel mills are the most common alternatives and are being put to use by some major cement and concrete companies such as Cemex. But rice husks, ground glass and several other alternatives can replace anywhere from 10 to 40 percent of the cement.
Canary media (2022) Major construction firms team up to get the carbon out of concrete
5.1 Growing limestone from algae
Simpkins
To make portland cement, the most common type of cement, limestone is extracted from large quarries and burned at high temperatures, releasing large amounts of carbon dioxide. Replacing quarried limestone with biologically grown limestone, a natural process that some species of calcareous microalgae complete through photosynthesis (just like growing coral reefs), creates a net carbon neutral way to make portland cement. In short, the carbon dioxide released into the atmosphere equals what the microalgae already captured.
Simpkins (2022) Cities of the future may be built with algae-grown limestone
5.2 Mud Constructions
Lewis
Concrete’s heat-retaining properties are all wrong for the Senegalese climate. Yet concrete has become the “traditional” building material in a country.
At least four distinctive mud-construction techniques persist. In the north, where there’s not much rain, people build houses with banco, a kind of adobe made with sun-dried bricks; in the forested areas of the south, builders use timber frames to create wattle-and-daub structures, or they hand-mold earthen buildings and top them with steep, overhanging roofs to keep rain away from the walls. For generations, Senegalese builders have used mud to construct not only small houses and granaries but multistory houses and imposing mosques.
Raw-earth-based building materials, such as adobe, rammed earth, and the compressed-earth blocks have more thermal inertia than concrete, which means they attenuate heat and cold more efficiently and reduce the need for so much air-conditioning.
Resistance to mud construction in modern Senegal goes beyond practical concerns: Earth-based materials are widely considered a symbol of poverty, a last recourse for those with no other shelter.
The accessibility of air-conditioning has created a kind of architectural laziness, because buildings no longer need to rely on design to stay cool.
In the nearby village of Ngawlé, Ousmane Mbodj and his family invited me into their banco house, and as soon as I stepped inside, my body relaxed. I had no instruments to measure the difference in temperature, but the change felt like a balm. Thick walls provide natural insulation from the sun, while the limited number of small windows helps the interior stay cool. Outside, thatch-covered verandas or perforated walls create shade and can be used as exterior rooms.
Roof leaks during the rainy season because the local mice like to eat its mud and hay.
In the center of Podor, the local département is constructing a mud-brick administrative building using the Nubian-vault technique. Originating from ancient Egypt, the method uses arches to create self-supporting adobe structures. The technique was revived in the 1940s by the Egyptian architect Hassan Fathy, who attempted to create a whole village of Nubian-vault structures on the banks of the Nile River. That project was never completed, but his approach, which he documented in his book Architecture for the Poor, created new interest in mud construction across the globe. In 2000, a French nonprofit called the Nubian Vault Association streamlined the technique and started training workers to employ it throughout West Africa—starting in Burkina Faso and expanding to Mali, Benin, Ghana, and Senegal.
An earth-construction boom is happening along the sunny coast south of Dakar. Here, earth construction is chosen not just by those with modest budgets and few other options, but by wealthier families with a taste for innovation and bespoke designs.
They had planned to build nearly 12-inch-thick walls for their thermal advantages, but the small lot could only accommodate 9-inch-thick walls. To make up for the difference, they positioned each row of blocks so that it protruded slightly over the row below it, resulting in walls that essentially create their own shade. The walls’ textured surface gives them a unique appearance—a style inspired by substance. Though houses like this are far too expensive for most, it illustrates both the practical and aesthetic advantages of mud construction.
Show people that we can build with local materials that will be much more comfortable and much cheaper than concrete.