Key Takeaway: As the global demand for concrete rises, a sustainable, environmentally sound solution is still decades away.

Concrete, the most widely used material on Earth, is poised to become even more plentiful as the world continues to urbanize. Global use of concrete is expected to rise by as much as 23% by 2050.

That poses a problem for our planet’s future: between manufacturing and the gasses concrete gives off, the material accounts for 5-8% yearly carbon emissions. If it were a country, it would be the world’s third-worst polluter, behind China and the U.S. 

As much as 90% of these emissions come from the production of cement, which binds the ingredients in concrete together. Kilns at cement factories heavily burn fossil fuels to heat limestone which, when it breaks apart, releases trapped carbon. That makes improving cement an urgent part of avoiding climate catastrophe. And there is a serious gap between urgency and action.

“[Concrete] is a quite slow-moving, difficult-to-change sector,” Felix Preston, a researcher at Chatham House, told the BBC last year. “It can take decades for a new standard to be approved and implemented.”

Nonetheless, researchers around the world are working to develop cement alternatives, and a handful of startups have attempted to put the results into production in recent years. Solidia created a cement formula that absorbs carbon dioxide as it hardens, reducing emissions by 70%; the company has a contract with a major cement producer, but is still in its pilot phase. Biomason uses bacteria to grow sand-based bricks, a zero-emission process, and is working to expand its reach beyond specialty contractors. MIT researchers have also announced breakthroughs.

Another longtime focus of research is magnesium-based cement, which offers the tantalizing possibility of a fully carbon-neutral binder. Last month, a team in Australia announced a potentially promising new development.The team, led by Western Sydney University engineering professor Sarah Zhang, works with magnesium oxychloride cement (MOC). Also known as Sorel cement, it’s been around since the late 1800s. Rather than using limestone, MOC uses byproducts of magnesium mining. Its chemical reaction doesn’t produce carbon dioxide, and oneingredient, magnesium oxide, can absorb carbon from the atmosphere. 

“Scientists have been at work on creating a truly ‘green’ cement for many years,” Zhang told Karma. “Our success could eventually be a game-changer for construction worldwide.”

Their announcement comes after three years of work addressing two major problems with MOC that make the material useless for construction projects. “Poor water resistance is its critical weakness,” Zhang said, “and corrosion resistance is also a major hurdle, as steel rebars have to be used in concrete.” Because of these attributes, MOC currently is used only for limited, indoor applications, like floor tiles and insulation.

Plentiful Materials

Last month, Zhang’s team announced a formulation of MOC that is fully water-resistant, with higher compressive strength than traditional Portland cement. Industrial byproducts, including fly ash and silica fume, were the key ingredients. Both materials are plentiful in industrialized countries including China, the US, and Australia. “With the water resistance significantly improved as a result or our research, MOC could be used more widely immediately,” she said – although not yet in construction, the most important application for any cement that hopes to reduce carbon emissions. 

That’s what her team is tackling now. Their next phase of research will attempt to formulate MOC that doesn’t corrode steel. In the meantime, they are looking for support from investors and the wider industry to speed up the process. Once the corrosion issue is addressed, implementation could happen quickly. “We can tailor the design to suit the needs of the industry,” Zhang said. “It will take about a year to develop the mix, and another year to test comprehensively.”

Despite their promise, magnesium-based cements have faced hurdles in the production stage. U.K.-based Novacem and American firm Calera both attempted to introduce MOC-like products but failed to get off the ground.  

Claude Lorea, the cement director at Global Cement and Concrete Association, an industry group, told Karma that there is room for MOC alongside other innovations in the fight against climate change. “Our view at the GCCA is that we will need the whole toolbox of low-carbon solutions, including novel binders,” he said.  

But promising as they may be, these alternatives are years, if not decades, away from widespread use. Because the world’s concrete manufacturing and safety standards are built around Portland cement, novel binders will “arrive in the market first as local solutions and for specific applications,” Lorea said, not instant replacements for large projects. Their safety and reliability are unproven, compared to cement’s hundreds of years of implementation. It can take decades of observation and testing to determine whether a construction material is safe for long-term use. 

As University of Sheffield researchers noted in 2016, “Care should be taken before magnesium oxide-based cements can be heralded as environmental saviors for the construction industry, as considerable research and development efforts are required before any of these cements could come close to providing a [sustainable alternative] for large-scale use in the 21st century.