The Future of Green Concrete

Concrete, the literal foundation of our built environment, is the most commonly used man-made material in the world. But its key ingredient – cement – has a carbon footprint that rivals the world’s biggest emitters. Under pressure to reduce emissions, the global construction industry is reckoning with an array of innovative, alternative cement products and production methods collectively known as “green” cement.

Perhaps unsurprisingly, “green” is a fairly loose term in this instance; to some, it can mean anything that is not traditional cement. Traditional cement production is responsible for 2.2 billion tons of CO2 emissions annually, which is good for 8 percent of the world’s total carbon emissions. ¹ Much of it occurs when raw materials, mainly limestone and clay, are heated in a kiln to over 2500 F to form a substance called clinker, which is then cooled, ground, and mixed with other materials to form cement, the binding agent that is used in ready-mix concrete. A full 90% of cement-related emissions can be attributed to clinker production, including the combustion of fossil fuels to fire the kilns as well as the chemical release of large amounts of CO2 from the raw materials during calcination (the heating process). ²

Traditional cement production is actually less carbon-intensive than it used to be, due to improvements in energy-efficiency and the use of alternative fuel sources such as waste biomass (often wood and debris from construction sites). ² There is also a move towards adding carbon capture, utilization, and storage (CCUS) equipment to existing plants, which could reduce emissions by up to 95 percent but has a considerable cost. ³

Other measures are also being utilized to cut down on total sector emissions. Supplementary materials such as fly ash, a waste product of coal combustion, and slag, a waste product of steelmaking, can replace some of the cement in concrete mixtures. Recycling existing concrete and using it in place of mined sand and gravel diverts further waste materials from landfills and reduces the overall environmental impact of the production process. ⁴

While each of these methods have been shown to reduce emissions, the fact remains that traditional cement production, in particular the production of clinker, will always release CO2 due to the fundamental chemical nature of the process. Rather than focus on abatement or carbon capture, some companies have reimagined the bounds of cement and concrete production and have begun experimenting with low-carbon, alternative solutions.

One such company is the North Carolina-based startup Biomason, which has developed a way to produce concrete that doesn’t result in any carbon emissions at all. Its trademarked biocement formula utilizes a solution of carbon, calcium, and other nutrients, along with a special strain of bacillus microbes, to build cement-like material, which is then used to bind together recycled stone aggregate much in the same way that coral and seashells are formed in nature. ¹ ⁵

This process occurs at room temperature, requires no heat or burning of fuel, and is completed within 72 hours. According to Biomason, their cement is three times stronger than traditional cement and is 100 percent recyclable The company’s first commercially available product is bioLITH, a brick-like tile that can be used for a variety of internal and external construction projects. ⁵

Bacteria-based cement alternatives like Biomason’s offer a further, almost unbelievable possibility: self-healing concrete. Theoretically, bacteria could be used to not only grow concrete but repair cracks that appear in the material over time. In 2016, the Defense Advanced Rearch Projects Agency (DARPA) launched the Engineered Living Materials program to further explore the potential of self-healing building materials. ¹

Other cement alternatives, including one produced by a Japanese company entirely out of food waste, are also in development. The challenge will be in convincing construction companies to actually use these new products. Green materials are typically more expensive than their traditional counterparts, and in the case of construction, there are significant safety and durability hurdles to overcome. ⁶

Global cement production is expected to increase by 23 percent by 2050, by which point 68 percent of the world’s population is projected to be living in cities. ⁶ ⁷ This increased demand will make it even more challenging for the cement industry to reduce its emissions, making green cement and other sustainable building materials an even more important part of the equation.