New Carbon Architecture by Bruce King

Author:Bruce King
Language: eng
Format: epub
Publisher: New Society Publishers
Published: 2017-11-06T05:00:00+00:00

Fig. 6.7: Starting with the same ancient technology — ramming — that gave us the Pantheon and the Great Wall of China (among many others), Watershed Materials makes its blocks with different sources of regional aggregate, then binds them with minimal cement to get strength and durability without the climate penalty.

Credit: © Jacob Snavely

More Ways To Reinvent Concrete

Many approaches to decarbonizing concrete seek to keep the enormous, complex, and expensive infrastructure already around Portland cement in place, but then offset its carbon emissions. The cement industry has already modernized and made production much more efficient, but there’s only so much you can do when your process requires baking huge quantities of rock to very high temperatures. One approach — CarbonCure — is to “supercure” concrete products like blocks and precast panels by exposure to liquid CO2 captured from cement plant emissions, essentially speeding up and magnifying the natural “soaking up” of atmospheric carbon that all concrete does over time.3

Another concrete innovation is borrowed from antiquity: compaction. Part of the secret to the longevity of historic Roman concrete, as well as historic rammed earth structures all over the world, is density. Whether you’re binding with clay, as in rammed earth, or lime-pozzolan cement, like the Romans, or even modern Portland cement, your concrete strength will increase with density because at the microscopic scale the binder doesn’t have to “stretch” so far to hold the aggregate together. To get higher density, you use less water, which also contributes strength, and then mechanically compact the damp mix. That’s how the Romans made their famous concrete, and that’s how rammed earth is made. The modern concrete industry recognizes this as roller-compacted concrete, as is used for massive unreinforced structures like dams, and also compacted soil-cement, as is common for road subgrades. Builder David Easton has been building and popularizing rammed earth in California and beyond for decades, adding Portland cement sometimes only to mollify nervous engineers and building officials. The strength of his compacted soil-cement (as it would be categorized in modern parlance) is impressive, for unlike ordinary concretes, it continues gaining strength for years and even decades. The process makes for beautiful walls of artificial sedimentary rock, but is quite labor-intensive and therefore expensive. Seeking to make it affordable, Easton applied the technology to a common product: the lowly but enormously useful concrete block, or cement masonry unit (CMU). His company, Watershed Materials, now makes compacted low-carbon blocks that can be used to replace CMU in many applications with both a better look and a much lower carbon footprint.

Yet another novel innovation, pioneered by companies such as Blue Planet and Calera, is to capture gaseous carbon emissions at cement, power, and metal plants and bind them as artificial limestone aggregate — carbon sequestering sand and gravel. This holds appeal for the carbon storage value, but also for the possibility of relieving pressure on quarries and riverbeds (as noted in earlier mention of “sand mafias”) where we currently harvest sand and gravel. It’s not

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