Concrete: The Elephant in the Room

The production of cement and concrete uses more resources than any other industry on the planet. Recent reports originating from the private sector estimate that 8 percent of total global greenhouse-gas emissions come from concrete — and that it is the second-most-consumed substance on earth after water.' A report by the Royal Institute of International Affairs notes: "To bring the cement sector in line with the Paris Agreement on climate change, its annual emissions will need to fall by at least 16 per cent by 2030." Direct emissions occur through calcination, when limestone is heated and breaks down into calcium oxide and carbon dioxide (accounting for 50 percent of total concrete industry emissions); indirectly, emissions occur when fossil fuels are used to heat the kiln (40 percent); and energy is also used for electricity to run plants and for transport (5 to 10 percent). Moreover, this still excludes the effects of aggregate extraction, running mixing plants, or water usage. In total, this process produces approximately 3.3 billion tons of carbon dioxide per year-over three times more carbon dioxide annually than the sum total of all global emissions related to airplane travel. Every ton of cement results in 800 kilograms of carbon dioxide emissions, primarily because the clinker must be heated to 1,800 degrees Celsius. On a building scale, this means each truckload of cement utilized for construction requires 22,000 tons of carbon dioxide to produce.

Even if concrete were able to be fully recycled, it still requires finite resources —for example, sand and gravel—to produce more. If one were to build a wall along the equator with all the sand and gravel mined each and every year to produce concrete, it would be 27 meters high. Thus, regardless of whether or not concrete can be branded as "green," or elements or components of it can be recycled, its production and distribution require an energy baseline that means it can never become truly sustainable. Although cement-based materials are vital for structural design in densely urban as well as earthquake-prone contexts, the reality is that their use remains disproportionately greater than is structurally or seismically necessary.

Building with earth and building with concrete are not mutually exclusive.
The philosophy we advocate in our projects and in this book is simply to utilize as little cement as possible. Comparing the comprehensive footprints of production for concrete and rammed earth support this assertion. Such footprints are referred to by economists in terms of externalities, namely the benefits or damages inflicted on a neutral third party during the production or consumption of goods or a service. Because building materials are evaluated according to such different parameters, it is difficult to cross-compare them, but, all things considered, the externalities of earth are largely positive while those of cement-based materials are almost entirely negative.

To elaborate: mineral resources are finite. Both concrete and rammed earth include gravel and sand, and both require immense amounts of energy to extract from the ground, whereas this expenditure is significantly smaller in the case of earth. However, these calculations further diverge in that the production of the cement prerequisite for concrete consumes significantly more resources through the aforementioned burning process. There are also fundamental differences in gray energy. If an earth building requires 1.8 tons of material— as was the case with Haus Rauch, for example — this necessitates 180 liters of water, energy for excavating the earth from the site, and energy for obtaining, transporting, and mixing any additional materials such as gravel. A project of the same volume executed with concrete would require 1.67 tons of material, between 147 to 347 liters of water, additional energy for excavation and transporting the unused earth from digging the foundations away, and even more energy for obtaining, transporting, and mixing the cement-based concrete and its aggregates. In addition, 1.9 British Thermal Units (BTUs) of nonrenewable energy are needed to fire the amount of cement for this mixture, as well as a further 85 to 157 liters of water. And, the water for the production of concrete is not gray water that can be recycled and reused, as it is with rammed earth: it contains toxic chemicals.

Moreover, in the case of concrete, significant economic and environmental costs are accrued due to building climate control and the maintenance throughout a building's life cycle. Climate control, particularly heating and cooling, contributes to energy use, as well as causing environmental dam-age. With air-conditioning, this is primarily because of noxious refrigerants and electricity use. Recent studies have indicated that the estimated 1.6 billion new air conditioners that will be installed by 2050 in countries like Mex-ico, Brazil, and India will significantly impact the ozone layer and contribute to climate change-which, paradoxically, will encourage the purchase of even more air conditioners. As economists Lucas Davis and Paul Gertler describe, not just the increased demand for electricity for these units will be problematic, requiring trillions of dollars in power generation and transmission infrastructure, but they will likely lead to shortages and price spikes in services." "In addition," notes climate scientist Nihar Shar of the Lawrence Berkeley National Laboratory, "most electricity worldwide continues to be generated using fossil fuels, so this growth in air conditioning means billions of tons of increased carbon dioxide emissions.“