When it comes to construction, concrete is king, but making it releases a lot of CO2—around 8% of global emissions. Demand for lower carbon emissions is creating a market for concrete with a smaller carbon footprint. The concrete maker Cemex is addressing that trend with what it says is the first net-zero CO2 concrete to be available worldwide.
Concrete packs a double wallop of CO2: manufacturers first have use fuel to heat limestone to 1,300 °C, and then the conversion of CaCO3 to CaO releases CO2 as a byproduct, explains Steven J. Davis, a professor of Earth system science at the University of California, Irvine. They further heat the CaO to 1,450 °C to sinter it with other components such as gypsum to form clinker, the cement that binds standard concrete together.
Cemex’s Vertua Ultra replaces limestone-based clinker with an alkali-activated alumina-silicate polymer matrix. Preparation of the binder doesn’t require high temperatures and doesn’t release CO2, dropping its carbon footprint by 70% compared to standard concrete, says Davidé Zampini, Cemex’s head of R&D. Cemex buys carbon offsets to make the concrete 100% carbon-neutral.
“I don’t think I’ve seen anybody else offering that yet,” says Ian Riley, CEO of the World Cement Association, a trade group. Riley says most concrete makers are reducing emissions through efficiency improvements, lower-carbon fuel sources, and partial replacement of CaO with industrial waste such as fly ash. Alternative binder chemistries aren’t as common and are mostly limited to prefabricated parts.
Cemex accelerated Vertua Ultra’s global release after successful launches in France in 2018 and the UK earlier this year. It is more expensive than standard concrete, but the lower carbon emissions are worth it for some customers. Zampini also says the polymeric binder makes it more resistant to acid and heat than standard concrete, a plus for applications like sewer pipes.
Jurisdictions such as Sweden, New York City, and California’s Marin County are putting policies in place to encourage low-carbon concrete, Riley says, but he’d like to see more. “I think that would accelerate change,” he says, and encourage commercialization of new cement chemistry.
Low-CO2 concrete is a growing market. In September, Amazon invested in CarbonCure Technologies as part of the online retail giant’s goal to be carbon-neutral by 2050. CarbonCure injects captured CO2 into wet concrete, which the firm says strengthens the final material. Solidia, which earlier this year expanded a partnership with the concrete maker LafargeHolcim, takes a similar approach, using captured CO2 to cure prefabricated concrete blocks and other components.