Concrete’s climatic consequences

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.

Author: Milan

In the spring of 2005, I graduated from the University of British Columbia with a degree in International Relations and a general focus in the area of environmental politics. In the fall of 2005, I began reading for an M.Phil in IR at Wadham College, Oxford. Outside school, I am very interested in photography, writing, and the outdoors. I am writing this blog to keep in touch with friends and family around the world, provide a more personal view of graduate student life in Oxford, and pass on some lessons I've learned here.

13 thoughts on “Concrete’s climatic consequences”

  1. Just look what concrete did to that young woman!

    Why, concrete! Why!?!

  2. 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.

  3. 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.”

  4. Concrete Is Remixed With Environment in Mind

    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.

  5. 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.

  6. 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.

  7. If steel is a big test, cement is an even tougher challenge. Cement is the world’s most widely used manufactured material, but cement works are typically small, scattered and undercapitalised, which makes them hard to press into service for the good of humanity. Demand for cement, which is mixed with water and aggregates to produce concrete, is set to soar in regions such as India and Africa. That means huge additional volumes of carbon dioxide will be generated. About 60% of the waste gas comes from producing clinker, one of the main ingredients of cement. This process, called calcination, involves heating ground limestone to more than 1,600ºC in a kiln, which produces calcium oxide and CO2.

    The clinker is ground and blended with other materials to form what is known as Portland cement; the power used for grinding also normally releases CO2. Nearly all of the remaining emissions come from the fuels used to heat the kilns, often coal or coke. These can be replaced with alternatives, from biomass to waste materials such as tyres and municipal solid waste (but not electricity, which at present cannot generate the high temperatures needed to produce the clinker). Along with efficiency improvements, that would be the quickest way to lower cement’s carbon footprint.

    ccs is a possible low-carbon option for capturing the CO2 from calcination and from the heat. McKinsey notes that the combined exhaust gases have low concentrations of CO2, making them more expensive to capture. The consultancy points to an innovative eu-backed project in Belgium called leilac that aims to redesign kilns to make it easier to capture exhaust gases from calcination.

    The bigger ambition is to develop clinker substitutes, which would do more to reduce emissions. A recent report by Johanna Lehne and Felix Preston of Chatham House, a think-tank, does not hold much hope for an early breakthrough on clinker. But having analysed 4,500 patents, it found that, surprisingly, “the cement sector is more technically innovative than its reputation suggests” (more than steel, for instance).

  8. Environmental impacts and decarbonization strategies in the cement and concrete industries

    The use of cement and concrete, among the most widely used man-made materials, is under scrutiny. Owing to their large-scale use, production of cement and concrete results in substantial emission of greenhouse gases and places strain on the availability of natural resources, such as water. Projected urbanization over the next 50–100 years therefore indicates that the demand for cement and concrete will continue to increase, necessitating strategies to limit their environmental impact. In this Review, we shed light on the available solutions that can be implemented within the next decade and beyond to reduce greenhouse gas emissions from cement and concrete production. As the construction sector has proven to be very slow-moving and risk-averse, we focus on minor improvements that can be achieved across the value chain, such as the use of supplementary cementitious materials and optimizing the clinker content of cement. Critically, the combined effect of these marginal gains can have an important impact on reducing greenhouse gas emissions by up to 50% if all stakeholders are engaged. In doing so, we reveal credible pathways for sustainable concrete use that balance societal needs, environmental requirements and technical feasibility.

  9. More than half the emissions involved in cement-making are a consequence of calcination, and most of the rest result from burning coal and other fossil fuels to power the process. All told, nearly one tonne of CO2 is released for every tonne of fresh cement.

    McKinsey, a consultancy, reckons reverse calcination could, at present, sequester up to 5% of cement’s emissions. As the technology improves it expects that might rise to 30%.

    And Calix, based in Sydney, Australia, is working on an electrically powered system which heats the limestone indirectly, from the outside of the kiln rather than the inside. That enables pure CO2 to be captured without having to clean up combustion gases from fuel burnt inside the kiln—so, if the electricity itself came from green sources, the resulting cement would be completely green.

  10. Greener graphene

    Graphene has indeed taken a slow road to find its place in the world (“Pouring graphene’s bright future”, May 21st). While the 30% increase in strength and other beneficial properties for concrete applications are certainly attracting attention, what has truly excited industry is the direct reduction in carbon-dioxide output during the cement manufacturing process. The biggest offender, but a necessary ingredient, in cement manufacturing, is something called “clinker”. It is the binding agent created in the way you outlined by roasting limestone and various compounds at high temperatures to burn off carbon.

    Advanced testing by First Graphene in conjunction with some of the world’s biggest cement-additive manufacturers shows that replacing the bulk of the clinker with very small amounts of graphene can reduce carbon emissions by up to 20% while, at the very least, maintaining the same performance characteristics as current cement products.

    michael bell
    Chief executive
    First Graphene
    Henderson, Australia

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