Concrete’s climatic consequences

2007-12-23

in Economics, Politics, Science, The environment

The tragic electrocution of Emily Horn

While aviation and ground transport get lots of well-deserved attention, in terms of their climate change impact, the concrete industry seems to get a lot less scrutiny. In a way, this is unsurprising; concrete is hardly glamorous stuff. At the same time, concrete production accounts for about 5% of all greenhouse gas emissions: mostly from the process of manufacturing clinker by heating limestone and clay. This is usually done using coal. The average tonne of concrete produced generates about 800kg of carbon dioxide: both as a result of the coal burning and the product of the chemical reaction involved (CaCO3 -> CaO and CO2, ignoring silicates). This figure does not include emissions relating to quarrying rock or transport.

Cement manufacture can be incrementally improved in three ways: by reducing the ratio of clinker to other additives, by making kilns more efficient, and by using fuels other than coal for the heating. All of these can make contributions, to a certain degree, but only a complete shift to biomass heating could have a terribly significant effect on greenhouse gas emissions (and that effect could be moderated by the emissions from transporting the biomass).

Demand for cement is growing at about 5% a year, and is partially driven by the construction of new hydroelectric dams and nuclear power plants. At present, the rate of demand increase exceeds the rate of efficiency improvements. As such, greenhouse gas emissions associated with concrete are increasing every year. The average North American home uses about 25 tonnes of concrete, mostly in the foundation.

George Monbiot discusses concrete in his book, focusing on geopolymeric cements as a solution. Carbon capture and storage (CCS) is theoretically possible, but with an added problem. Concrete plants must be sited near limestone quarries. These are not necessarily near the salt domes or aquifers where CCS can probably be most effectively deployed. Geopolymeric cements are similar to the pozzolan cement used by the Romans to build the roof of the Pantheon. They are made from clay, certain kinds of sedimentary rock, and industrial wastes. Producing them generates 80-90% less carbon dioxide. This is because they require a lot less heating and the chemical reaction that produces them does not generate CO2 directly.

The modern version of this material was only developed in the 1970s and has yet to be widely adopted. Partly, that is because of the cost of refitting existing cement works or building new ones. Partly, it reflects the hesitation of the construction industry to use new materials. Such objections can probably be most efficiently addressed through carbon pricing. If the concrete and construction industries were paying for those 800kg of CO2, the incentives they face would probably change decisively and fast.

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{ 6 comments… read them below or add one }

Anon December 23, 2007 at 2:58 pm

Just look what concrete did to that young woman!

Why, concrete! Why!?!

tristan December 27, 2007 at 1:07 am

As with any construction issue, one has to look at the carbon produced by the building material in relation to the amount of time buildings made with the material will last. Concrete is an awful material, it will not last 200 years. In addition to losing its strength over time, it is porous and because of this rebar used to reinforce it rusts.

. June 12, 2008 at 1:25 pm

Making cement from biomass energy

Lafarge North America Inc., the continent’s largest maker of cement, hasn’t made many friends within environmental groups. In Ontario, for example, the company has aggressively pursued a plan to burn old tires to provide energy for its cement-making operations. While there’s much debate over the value of doing this — some, including the U.S. Department of Energy, argue that burning rubber tires is better environmentally than burning coal or oil — clearly the idea of burning tires rather than recycling them into other useful products is frowned upon by many.

Perhaps in an attempt to green up its image, Lafarge announced this week it has partnered with Kingston, Ont.-based Performance Plants Inc., a biotech firm that has patented processes for growing certain non-food crops and grasses on unproductive farmland and with the ability to withstand extended droughts and heat waves. Under its four-year partnership with Performance Plants, Lafarge will grow and develop clean-energy biomass grasses and woods for use as fuel at its cement plant in Bath, Ontario. “Our challenges with biomass and biofuel energy are maximization of crop yields, crop consistency and cost efficiency,” explains Peter Matthewman, president of Performance Plants. “This is where our technology will be instrumental to develop next generation seeds that are customized for specific industrial users looking for alternative clean energy sources.”

. April 2, 2009 at 11:03 am

Concrete Is Remixed With Environment in Mind

By HENRY FOUNTAIN
Published: March 30, 2009

In his mixes, Dr. MacDonald replaced much of the Portland cement with two industrial waste products — fly ash, left over from burning coal in power plants, and blast-furnace slag. Both are what are called pozzolans, reactive materials that help make the concrete stronger. Because the CO2 emissions associated with them are accounted for in electricity generation and steel making, they also help reduce the concrete’s carbon footprint. Some engineers and scientists are going further, with the goal of developing concrete that can capture and permanently sequester CO2 from power plants or other sources, so it cannot contribute to the warming of the planet.

. October 13, 2016 at 12:25 am

THE cement industry is one of the world’s most polluting: it accounts for 5% of man-made carbon-dioxide emissions each year. Making this most useful of glues requires vast quantities of energy and water. Calcium carbonate (generally in the form of limestone), silica, iron oxide and alumina are partially melted by heating them to 1450°C in a special kiln. The result, clinker, is mixed with gypsum and ground to make cement, a basic ingredient of concrete. Breaking down the limestone produces about half of the emissions; almost all the rest come from the burning of fossil fuels to heat the kiln.

As almost all big cement firms also produce building materials such as concrete and asphalt, capturing emissions to create such products is worthwhile. It could also reduce open-pit mining for limestone, which is especially destructive. Blue Planet is providing materials for San Francisco’s new airport and has other projects across North America. Concrete is the “900-pound gorilla in the carbon footprint of any building” says its CEO, Brent Constanz.

. July 5, 2017 at 5:16 pm

Ancient Romans made world’s ‘most durable’ concrete. We might use it to stop rising seas.

A bunch of half-sunken structures off the Italian coast might sound less impressive than a gladiatorial colosseum. But underwater, the marvel is in the material. The harbor concrete, a mixture of volcanic ash and quicklime, has withstood the sea for two millennia and counting. What’s more, it is stronger than when it was first mixed.

The Roman stuff is “an extraordinarily rich material in terms of scientific possibility,” said Philip Brune, a research scientist at DuPont Pioneer who has studied the engineering properties of Roman monuments. “It’s the most durable building material in human history, and I say that as an engineer not prone to hyperbole.”

By contrast, modern concrete exposed to saltwater corrodes within decades.

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