A weighty question indeed. When we consider the ecology of human expansion, certain raw materials are the fuel of social and economic transformation. The insatiable appetite of the industrial revolution of the 19th century was fed by coal and wood. The arrival of the 20th century ushered in the petroleum era, steel construction and the transformation of night by the incandescent bulb. As architectural capacities expanded and revolutionaries such as Corbusier discovered the wonders of poured aggregate as a building and surfacing material, the menu of modernism was expanded to include concrete and the “brutalist” architectural movement was launched. Our urban landscapes are characterized by the presence of concrete structures and surfaces.
Concrete, a rich aggregate of stone and sand, is held together by cement and is used as a building material nearly everywhere. Roads, building foundations and facades, sidewalks and decorative sculpture can all be comprised of concrete. Los Angeles is famous (infamous?) for its rivers lined with concrete lined sluiceways. Reinforced and stabilized by a metal lattice, referred to as rebar, reinforced concrete provides relatively cheap and resilient service to the building trades and people who use them. Early forms of concrete have a long history. The Romans and Greeks used a form of unreinforced concrete before the Christian Era – the Parthenon is the largest structure ever built with that early form of concrete. The term cement was actually coined in 1750.
The production and use of concrete carries a high environmental price tag – especially with respect to the production of greenhouse gasses in its making and in the release of dust in it’s destruction. The story is complex however and the idea of sustainable concrete is not actually an oxymoron. The value equation involves how hot the temperatures are in the production of cement and the cement’s fate after it is no longer in use. Calcium carbonate (CaCO3) is a key ingredient in cement and during the production process, it is broken down into lime (CaO) and carbon dioxide (CO2). Carbon dioxide is emitted directly from this process and accounts for about 50% of the greenhouse gasses produced in the making of cement. The other “half” is dependent on the source of the heat, such as coal or natural gas, used to drive the chemical reaction. The temperatures are high (typically 1500 degrees Fahrenheit), in order to produce alite (Ca3SiO5) which acts like the glue holding the concrete together. New technologies are being used to create similar glues at lower temperatures. Lower temperatures will emit fewer greenhouse gasses, regardless of the fuel used.
A recent article by Ana Swanson in the Washington Post, cites statistics from the Gates Foundation and the International Cement Review that point out just how central cement is to the growing post-modern societies of the world. The United States used 4.5 gigatons of cement in the 100 years encompassing the 20th century. That is a tremendous amount of cement. A ton is 2000 lbs. So, the amount were discussing here is 2000 x 109 lbs. of cement. That’s right 4.5 billion tons of cement.
However, the staggering revelation in her article was that China has used more cement in the past three years than the United States consumed in a century of economic expansion. That’s right, over 6.5 gigatons of cement consumed by Chinese infrastructure expansion in the three years from 2011-2013. According to Rhett Allain from Wired , that represents a slab of concrete the size of Hawaii. The fascinating elements here are two fold; 1) the non-linear way in which ecosystems change, and 2) the pace of human migration that this level of building is designed to support. Approximately 1.5 million Chinese people move from rural dwellings to the cities each month. This mass migration represents an unprecedented movement of humans, resulting in a massive acceleration of demographic trends. The resulting impact on the on the environment is equally profound. In many ways, we lack even the scientific tools to assess change at that scale.
About the Author: Dr. Eric Strauss serves as President’s Professor of Biology at Loyola Marymount University and Executive Director of CURes. With collaborative research specialties in animal behavior, endangered species management, urban ecosystems and science education, Eric has extended the model for faculty scholarship by co-founding the Urban Ecology Institute in Boston while he served as a faculty member at Boston College and CURes in LA, both of which provide educational, research and restoration programs to underserved neighborhoods and their residents. In addition, Dr. Strauss is the Founding Editor of a web-based peer-reviewed journal, Cities and the Environment, which is funded in part by the USDA Forest Service. His research includes collaborative long-term studies of coyotes, White tailed deer, crows, turtles and other vertebrates, with a specialty in understanding wildlife in urban areas and the appropriate management responses to wildlife problems and zoonotic disease. His work also includes investigating the role of green space and urban forests in supporting of healthy neighborhoods and how those features can be used to improve science education and restorative justice. He has co-written multi-media textbooks in biology and urban ecology as well as hosting multiple video series on the life sciences and ecology. Dr. Strauss received his BS in Mass Communication from Emerson College and Ph.D. in Biology from Tufts University in 1990.