Microsoft co-founder Bill Gates has written a new book titled “How to Avoid a Climate Disaster,” and in it he argues that we need to get serious about changing the way we produce cement if we’re going to tackle climate change. Gates says that cement – one of the most common construction materials – is responsible for 6% of carbon emissions globally.
Sriramya Nair, an assistant professor of civil and environmental engineering, is working to develop new alternatives to cement that decrease emissions, yet meet construction demands. Nair says that demand for construction material will increase in the coming decades and that researchers are exploring cement alternatives derived from waste material such as corn ash or rice husk ash.
Nair says:
“In 2020, 4.37 billion tons of portland cement was produced worldwide and production of one ton of portland cement generates an average of 0.9 tons of CO2, resulting in approximately 5-7% of the global CO2 emissions. Cement production plants are finding ways to curb CO2 emissions, but to reach net zero, more needs to be done.
“Thanks to decades of research and scientific developments, in many infrastructure projects a large portion of the binding agent, portland cement, is successfully being replaced with waste such as high-quality fly ash generated from burning coal in power plants, blast furnace slag from the refining iron and steel, and finally silica fume, a byproduct from producing silicon or ferro-silicon alloys.
“With a worldwide shortage of high-quality fly ash and with significant quantities of slag having to be shipped from Asia, it is essential to find alternate, ideally locally available resources for replacing portland cement. Examples of such alternatives include mining waste, coal bottom ash, rice husk ash, corn ash, incinerated municipal solid waste ash, wood ash etc. Researchers are also developing alternate cementitious materials that can be used as a complete replacement to portland cement. Most of these efforts are limited to laboratory research and there is a need for a change in the construction industry to enable reliable use of waste materials in infrastructure projects in conformance with public building codes.”
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Kenneth Clark Hover, a professor of civil and environmental engineering, is an expert in anlyzing and rehabilitating deteriorated concrete. Hover cautions that innovations and alternative building materials that are more environmentally friendly still need to be safe and that there is precedent for innovations that have resulted in collapses.
Hover says:
“Many innovative materials are under consideration as cement-substitutes or supplements. A few have been around for many years and are in common use. Many of the newer candidates are extremely promising in lab and short-term field studies.
“For structural applications, where life safety depends on the continued, long-term serviceability of the material, we must have confidence in that innovative material, supported by more than extrapolated short-term lab tests. Right now, few of the proposed innovations have a proven (not calculated) track record under environmental exposure to hot, cold, wet, dry, repeated freezing and thawing, exposure to seawater or to deicing salt. Few of the proposed innovations have demonstrated volume stability, tolerable shrinkage or expansion with wetting or drying or temperature changes, long-term creep, or fire resistance. We know little of their response in earthquakes or shock or explosions. There are precedents for well-intentioned innovations that resulted in collapses.
“If we were manufacturing hand-held devices with an expected 3 to 5 years’ service-life before technical obsolescence, we could tolerate our lack of confidence in longer-term behavior. For some infrastructure applications, like a parking lot for example, if it comes apart in a few seasons, it may be expensive to replace, but nobody dies. If it was a parking garage or office or university building, an arena, bridge, hospital, apartment building, home, or school, would we be satisfied to know only that the innovative material survived short-term laboratory tests?”
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