水泥生产贡献约6%的global greenhouse-gas emissions, say scientists who are trying to chip away at the pollution problem. Two start-ups, one in Canada and another in Arizona, are among the newer entries in the effort to produce cleaner cement and concrete.

WAGNER

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类似于当今化学混合物的管道方式，将设备改装到混凝土搅拌机上₂进入混凝土。“当₂is added to the concrete during mixing, the CO₂该公司的网站说：“与水反应形成碳酸盐离子。然后，碳酸盐迅速与从水泥释放到迅速形成石灰石状材料的钙离子反应。该矿物是以分散在混凝土混合物中的纳米材料形式产生的。”

The conversion of CO₂气体到固体碳酸盐永久隔离混凝土中的气体。该公司在砖石领域工作了几年，但刚刚开始使用该技术进行现成混合。瓦格纳说：“我们预计到今年年底将有几个完全运行的现成混凝土装置。”

CarbonCure sequesters different amounts of CO₂, depending on the individual producer's mix design, Wagner adds. "Typically, the amount of CO₂that is sequestered is around 1% of the weight of cement," she explains. "In ready-mix-concrete applications, the addition of CO₂还可以解锁材料性能增强功能，这可能导致混合设计优化，并进一步加以实现。₂reductions."

STONE

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Stone stumbled on this discovery in 2002, while pursuing a doctorate at the University of Arizona. "It has taken years to get just a basic understanding of the chemistry involved," he says. Waste steel dust makes up 60% of the material's dry ingredients; fly ash is 20%, and ground limestone is another 10% of the mix. Exposing the dry ingredients to water and CO₂at ambient temperature "drives the oxidation reaction that forms the cementing iron-carbonate mineral matrix," Stone says, adding that hydrogen gas "is a by-product that might be harvested at large-scale operations."

由此产生的糊状物具有令人印象深刻的品质，达到5,500至6,500 psi，“尽管我们已经达到了10,000，”斯通说。经过四天的水和CO固化₂exposure, Ferrock can reach strength comparable with portland cement after a 28-day moist cure; full strength is achieved in 10 days. Flexural strength tests have shown Ferrock to be up to seven times stronger than portland when both test specimens have 1% glass fibers. With these qualities as the potential prize, Stone and Narayanan Neithalath, associate professor and civil engineer at Arizona State University, are conducting research to improve the product.

费罗克的主要弱点是“由于CO的扩散，反应的缓慢₂into the interstitial water in the thick paste and the subsequent formation of iron carbonate," Stone concedes. Using a method that has been effective at carbonating slabs, walls and other thick structures, the gas is injected into the fresh paste via embedded thin-walled steel conduit perforated every four inches with ¼-in.-dia holes. Crushed-stone aggregate is needed to make the poured material porous and allow the CO₂to permeate it, but "some strength is sacrificed with this method," Stone says. "We are working on ways of introducing all of the CO₂initially, along with the water, to make the subsequent gassing unnecessary."

Storage, preparation, delivery and placement of Ferrock are conventional but with different materials. In the dry state, Ferrock is just like portland cement, Stone says, noting, "After mixing with water, it will not harden until exposed to CO₂或者允许干燥，这可以在空气中进行氧化。需要孔隙率，可以将玻璃粉碎成各种尺寸的聚集体并代替混合物中的沙子和砾石。不需要倒塌测试。，“ Neithalath不是反应中的试剂。您需要水均匀地分散颗粒，并将二氧化碳携带在材料中以形成这些结合剂。”

Despite its promise, Ferrock faces a major hurdle in gaining industry acceptance. To overcome market inertia, the challenge of meeting engineering properties and the resistance of standard-setting organizations and users reluctant to bet their million-dollar project on an unproven material, "it takes a long time for the industry to accept change," says Steve Kosmatka, vice president of research and technical services for the Portland Cement Association. Portland cement was invented in England in 1824 but was not widely used in the U.S. until the 1860s, he notes. Its advantages over natural cement were so great that it became the standard, but it still took decades. Supply of key materials is a further challenge, Kosmatka and Stone concur. Waste steel dust from large steel shot blasting has met the needs for research, but, "on a large scale, we might tap the direct reduced iron supply, which is huge, but it's a feedstock for steel production and not a waste, so it's much more expensive," Stone says.

这家加拿大公司CarbonCure Technologies Inc。Dartmouth, Nova Scotia, provides a technology to masonry and ready-mix-concrete producers that sequesters waste carbon dioxide (CO) into concrete, says Jennifer Wagner, vice president of sustainability. "The process works with any type of conventional cement," she notes. As with CarbonCure, most "green" concretes start with conventional portland cement. Ferrock, which uses steel dust as its basic component, takes a different approach. While portland-cement production requires substantial energy—much of it from fossil fuels emitting CO—Ferrock requires no energy input. "The embodied energy in the reduced iron drives the oxidation reaction," says David Stone, the inventor and founder of Iron Shell LLC, the Tucson-based company that is working to commercialize the technology.