Cement is at the heart of increasing global warming emissions. It's production releases large amounts of CO2 -- both from the chemical process that creates it and the energy consumed in manufacturing. China alone makes 45% of the world's cement, and globally the industry is booming.
That's why two promising new developments related to the production of cement - an ancient and mundane material -- are drawing attention. Reducing CO2 from making cement isn't as sexy as electric cars, but it's the third largest US CO2 producer so there’s an opportunity to make a real contribution.
Cement is at the heart of increasing global warming emissions. It's production releases large amounts of CO2 -- both from the chemical process that creates it and the energy consumed in manufacturing. China alone makes 45% of the world's cement, and globally the industry is booming.
That's why two promising new developments related to the production of cement - an ancient and mundane material -- are drawing attention. Reducing CO2 from making cement isn't as sexy as electric cars, but it's the third largest US CO2 producer so there’s an opportunity to make a real contribution.
Calera - cement from CO2
A venture capital funded company, Calera, is using the CO2 in the flue gas from a gas power plant to make cement. This both reduces the pollution from making cement and actually sequesters some of the CO2 in a useful product. From the Sceintific American story:
<span style="font-size: small; font-family: Times New Roman">Today, this flue gas wafts up and out of the power plant's enormous smokestacks, but by simply bubbling it through the nearby seawater, a new California-based company called Calera says it can use more than 90 percent of that CO2 to make something useful: cement.
It's a twist that could make a polluting substance into a way to reduce greenhouse gases.</span>
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Calcium in the seawater combines with the CO2 to make a slurry of calcium carbonate, which is then dried with waste heat from the 700 degree F flue gas. This sequesters a half-ton of CO2 produced in the manufature of each ton of cement, so making this cement actually has the net effect of reducing CO2 in the atmosphere.
Cement, also called Portland Cement, is a gray powder that is mixed with water, sand and aggregate to make concrete. In casual speech, people frequently confuse cement and concrete. It’s actually a very energy intense product that creates 1 - 2% of US CO2 emissions and worldwide it's even worse, accounting for 5% of the total. The global number is higher largely because of China, which is doing a lot more building than anyone else. China produced 40 to 50% of the world's cement last year and unfortunately mostly uses less efficient plants.
Carbon Sense Solutions
About 400 lbs. of CO2 is created for each cubic yard of concrete. The Portland Cement Association says that about 60% of the CO2 comes from a process called calcination, which uses very high heat to drive off the CO2 in limestone. Concrete re-absorbs a lot of that over its lifetime, about 60% of it over 100 years. The rest will be reabsorbed eventually if the concrete is crushed to recycle it and the inside bits get exposed to air.
Carbon Sense Solutions in Canada has found a way to speed up that slow reabsorption in pre-cast concrete. The MIT Technology Review reports that they expose the freshly mixed concrete to CO2, once again from flue gas, to cure the concrete. This also saves significant energy over the typical curing with heat or steam. So that’s a second two-fer technology: it absorbs a lot of CO2 fast and avoids the big energy consumption used by the usual process. A pilot plant is being built in Nova Scotia this summer. Robert Niven, the founder said
<span style="font-size: small; font-family: Times New Roman">If it works and is widely adopted, it has the potential to sequester or avoid 20 percent of all cement-industry carbon-dioxide emissions,</span>
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These are two great ideas but don’t expect to see big changes in the concrete industry right away. First, they are still in the trial stage and second, the concrete industry is famously slow to change.
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Cement Industry Is at Center of Climate Change Debate (New York Times)
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