Concrete

Concrete is cement with sand and rocks added. This is about cement. Made of silicate rocks, limestone rocks and a lot of heat. Add water and those other ingredients to cement and make new user-defined concrete rock shapes.

This new rock absorbs CO2 from the atmosphere. This is well known, but got a publication in Nature Geoscience (not a shabby journal) last November. But user-defined rocks (e.g., buildings) may be of ~100 meter dimension and therefore have little surface area.

Brings us to China, where very many old buildings are being converted to rubble (and land-filled) so new, bigger, higher-rent buildings can be made. This rubble (from which steel rebar is removed and recycled) has much smaller particle size, thus much more surface area. But bulked into landfill environment is not ideal for CO2 absorption.

Use a bit more energy to make ~0.5 mm particles, remove bricks as convenient (they are reformatted clay and don’t absorb CO2), and you have the material of interest. This, placed in soil, absorbs a lot of CO2, because soils have high CO2 concentrations. There have been studies of this as well, but very limited and only trialed in ‘brownfield’ (i.e., trashed) soils.

My idea is to amend this material to agricultural (and perhaps forest) soils where it will sequester CO2. Less returning to the atmosphere, and done faster than from a single large rock. In low-pH soils it may not work that way, but instead add calcium (originally from the limestone) that should benefit those soils in a different way.

Not done before and particularly not in China, world’s greatest producer of concrete rubble. Questions remain: Will different plants growing in different soil types and climates be happy about this amendment? How much CO2 is actually sequestered and with what dynamics? Purpose of research (funding) is to answer such questions. I plan to take this on the road and talk to various research institutes here. It is ‘applied research’ and not all shops are into that.

Walk down the street in Kunming and soon encounter a demolition site. It is no trouble to collect samples for seminar-display purpose.

If every bit of cement ever made ended life in this way, the process would be geochemically carbon neutral. Not energetically carbon neutral, because melting rocks at step one took a lot of energy. So, no one need fear that I might deprive plants of +CO2 they are currently enjoying. Just a bit of it.

Waste is ‘waste’ to the extent that its values have not yet been exploited.

 

Please explain your meaning, drysider. Your post is refreshingly short compared to mine, but too short to decode.

 

Just so. I propose shallow burial of cementitious particles, within the plant rooting zone, specifically so that water and CO2 can get to them.

Air in void volumes of shallow soils contains ~5% CO2. When not utterly dry, this is a good setting for CO2 sequestration.

 

Just so. Beach sand is often quartz, a most unreactive mineral. Land processes above revise other minerals (their 'goal' often being clay), and the restless sea gets particle sizes down to desired range.

Smallest particles in concrete mix need to be unreactive because they have high surface area. (Aggressive chemistry happens when you mix cement and water) Larger gravel and rocks (run of crush) can be almost anything because much less surface area.

Concrete recipe requires small particles as well as larger ones. If your local geology offers sand only from beaches, that's where you'll get it.

 

Or maybe sand from recycled glass? It's quartz with Na, Ca and Al oxides added; still nicely unreactive. Despite our best efforts to consume glass-bottled products, still way less than concrete industry requirements.

 

Sure. If you want quartz-like rock for any reason, and lack a beach, deserts are handy . There the same uphill geochemical sorting takes place, but the grinding step is wind not water.

Glass is such an interesting thing that I am avoiding temptation to derail this concrete thread. But I know y'all hate chemistry. But fiberoptics and germanium! Temptation strong.

 

Chemistry of colored glass has strong (but incomplete) relationships with chemistry of colored fireworks. Temptation strong....