The Third Little Pig built his house of bricks…..
Our modern world is increasingly built of reinforced concrete. Almost every building foundation, bridge and dam are built of it, as well as countless other smaller structures. The problem is that the two primary ingredients — steel and cement — produce lots of greenhouse gasses. By most estimates, 8% of worldwide CO2 emissions come from reinforced concrete construction — over 4 billion tons annually! If we are to reduce the impact of climate change, this number will need to be dramatically reduced.
Reinforced concrete consists mainly of concrete: a mixture of a binder (usually Portland cement) and an “aggregate” (usually sand and crushed stone). Concrete has impressive compressive strength and stands up well to environmental weathering, but cracks easily under tension. To fix this problem, steel is imbedded in the concrete. The steel is protected from corrosion by its concrete shell, making a marriage that is greater than the sum of its individual partners.
PROBLEM ONE: CEMENT
Portland cement is made primarily from limestone which is heated to very high temperatures. Fossil fuels are used to create the necessary high temperatures, releasing substantial CO2. In addition, limestone itself (calcium carbonate) is a form of sequestered carbon — marine organisms use CO2 dissolved in sea water to make their shells. Over the eons, these shells settle to the ocean bottom removing vast quantities of carbon from the atmosphere. When limestone is heated, that CO2 returns to the atmosphere.
In the end, nearly a pound of atmospheric carbon dioxide is released for every pound of concrete poured into construction sites around the world. If you have ever lifted a cement block, you know that is a lot of pounds!
PROBLEM TWO: STEEL
In addition to reinforcing concrete, steel is used for thousands of other things. New steel is made by heating iron ore to very high temperatures, generally using — take a guess — fossil fuels, notably coal. The process can produce almost two pounds of CO2 for each pound of steel. Currently, steel production is responsible for at least 6% of global greenhouse gas emissions.
New steel is mostly needed in rapidly growing countries such as China and India. Countries with more mature infrastructure, like the US and Europe, can largely fill their steel needs with recycled steel, which can have a much lower carbon footprint. But there are many countries in dire need of infrastructure development, so the demand for new steel will continue.
GREEN CONCRETE AND STEEL
The good news is that, unlike the fossil fuel industry, the titans of steel and cement production have been doing good work to develop products with much lower climate impact. Partnering with research efforts in universities around the world these industries have come up with an impressive array of new paths forward, each having pros and cons, each jockeying for a position in the green building revolution that is already underway. The steel and cement industries will still need lots of energy, but that will need to quickly start coming from renewable electricity and green hydrogen.
For a deeper dive on green cement: The Constructor
A Spanish energy conglomerate explains green steel: Iberdrola
The Second Little Pig built his house from sticks…..
As a structural material, wood has applications well beyond stick frame housing, and is starting to be used for things like bridges and high rise buildings. Trees remove carbon from the atmosphere to make their roots, trunks and branches, and as long as that wood is kept from burning or rotting, the carbon remains sequestered.
Read about the world’s tallest wooden highrise: Architectural Digest
The First Little Pig built his house from straw…
Bamboo, a type of grass, also has amazing engineering properties. In its native habitat (primarily Asia) it has been used in its natural state for millenia as a strong, lightweight and abundant building material. With the compressive strength of concrete and the tensile strength of steel, engineered bamboo could have many applications. Using modern adhesives, products like cross laminated bamboo panels, woven bamboo lumber and cored wall panels will be showing up at construction sites soon. As with wood, structural bamboo products store carbon if kept from rotting or burning. See: BamCore
Thanks for reading,
Doug Hylan, Brooklin, Maine
Atmospheric CO2 today: 421.15 ppm. One year ago 419.09
“We’re at the point where it is cheaper to save the planet than to ruin it.” Billionaire venture capitalist John Doerr
Hi Doug! My builder friend began using bamboo flooring in some of his high end custom homes. The buyers wanted to try a more renewable material. The idea was great but the problem was: bamboo splinters quite easily. Over the period of a couple of years, the bamboo flooring started to come apart. The family got a lot of splinters in their feet. So all new flooring had to be installed. The builder is someone I know well. He would never use cheap materials. I think that people should be careful where we use bamboo for now. Over time materials will improve. We think that a combination of wear and tear plus the dampness left after floor washing caused this. But we don’t know for sure. I love bamboo in many applications. Just not floors for now.