MIT researchers have discovered a groundbreaking method to make concrete production more environmentally friendly, without affecting its mechanical properties. Concrete, the world’s second most consumed material, contributes to 8% of global CO2 emissions. By adding a simple, inexpensive ingredient – sodium bicarbonate (baking soda) – to the concrete manufacturing process, up to 15% of CO2 emissions associated with cement production can be mineralized during the early stages. This innovative approach involves forming carbonates during mixing and pouring, before the material sets, eliminating the detrimental effects of CO2 uptake after curing. The resulting composite of calcium carbonate and calcium silicon hydrate doubles early-stage concrete’s mechanical performance, allowing for quicker setting and increased construction industry productivity.
Enhancing concrete’s carbon sequestration potential
Forced carbonate mineralization during early cement hydration stages offers potential for CO2 sequestration. While late-stage carbonation leads to decreased structural integrity, early-stage carbonation improves strength and resistance to chloride permeability. By incorporating sodium bicarbonate into the cement formulation, researchers found that precure carbonation doesn’t deteriorate structural integrity and incorporates up to 15 w% CO2 as calcite and a CaCO3/C-S-H composite phase. These findings pave the way for a more sustainable approach to concrete production by reducing its environmental footprint.
Looking for concrete alternatives
The MIT research comes at a time when many builders are seeking alternatives to concrete due to its CO2 footprint. Mass timber, which involves gluing pieces of softwood together to form larger pieces, is one such alternative. It can also increase demand for sustainably managed forests, which can absorb more carbon. While mass timber is gaining popularity, concerns about long-term durability, potential for increased deforestation, and lack of standardized measurements for assessing embodied carbon remain.
Concrete was seen as the epitome of modernity in the mid-20th century, with Switzerland leading the way by consuming more concrete per capita than other European countries post-WWII. Swiss engineer Robert Maillart designed concrete bridges, and Swiss architect Le Corbusier used raw concrete in the Brutalist architectural style.
Nowadays, concrete has a much more negative image, not only due to its environmental impact but also because of its architectural use. The term “concrete jungle,” referring to post-war city expansions, is not exactly a positive term. These new developments may change the way we look at concrete once again.
Embracing a sustainable future
MIT’s groundbreaking research on incorporating sodium bicarbonate into concrete production, combined with other recent innovations in lower carbon footprint concrete admixtures, could provide much greener and even carbon-negative construction materials for the built environment. These developments, along with the increasing popularity of mass timber, signal an optimistic future for sustainable construction materials and practices, transforming concrete from a problem to a part of the solution in addressing climate change.
