Coal news and updates

Over the truly long term, Earth’s climate has a geological thermostat built in that helps moderate change. If things get warmer, chemical weathering of exposed rock speeds up—a reaction that gradually removes carbon dioxide from the atmosphere. But on a timescale much more relevant to our lives, there is actually something sort of similar going on. Humanity’s aging concrete infrastructure is taking up CO2, too. It’s not a huge amount, but it’s not nothing.

 

The manufacturing of cement produces CO2 emissions. The raw material that goes into cement is principally limestone—calcium carbonate. At high temperature, molecules of CO2 escape, leaving just calcium oxide behind, which is what we call “lime.” So in addition to the burning of fossil fuels to heat the material, you’re converting some bedrock (the calcium carbonate) into atmospheric CO2.

 

But this process gets reversed as cement sits around and slowly deteriorates—the lime reacts with water and atmospheric CO2 to make calcium carbonate again. While researchers doing the accounting for global greenhouse gas emissions have worked carefully to track the CO2 produced by cement manufacturing (it kicks in about five percent of total fossil fuel and industry emissions) the reverse process has never really been tallied at a global scale.

 

A new study led by Chinese Academy of Sciences researcher Fengming Xi sought to fill in that gap. Adding a new set of measurements from cement in Chinese structures to existing studies elsewhere, the researchers put together a chemical model with estimates of things like exposed surface area, weather conditions, and structure lifespan. The result is a global estimate of how much atmospheric CO2 has been sucked up by decaying cement during its life, demolition, and re-use or disposal.

SOurce:arstechnica