In a two-part series, the American Concrete Institute (ACI) President, Charles K. Nmai, discusses the various solutions to the high carbon concrete that is most widely used today in hopes of reducing to carbon-neutral. One way Nmai points out that can help carbon production from cement be reduced is through Supplementary Cementitious Materials (SCMs) like fly ash, slag cement, calcined clay, also known as metakaolin, silica fume, and natural pozzolans. He notes that these methods are already used throughout the world and other SCMs such as rice husk ash and ground-glass pozzolans can be available based on locale. Though these methods of replacement have been around in the concrete industry for a while, Nmai points out that they have not replaced regular, high carbon concrete. He specifically points out that in most of the projects to date that have used SCMs extensively, the push to do so came from the owner rather than the builder. Nmai then goes on to encourage design professionals to follow the example set by owners and invest in SCMs to reach carbon-neutral concrete.

 
In his second memo, president Nmai elaborates on some of the problems with current attempts to achieve carbon-neutral concrete. The main things he focuses on relate to availability of SCMs based on location, lacking storage in concrete plants for SCMs, and more downsides that all add up to making SCMs more expensive and therefore less appealing for designers and owners. Nmai goes on to call for more studies to be conducted using SCMs and other carbon-neutral concrete materials because many building codes call for rigorous testing before such replacements can be utilized in a project. He concludes by stating plainly that while there have been many additions to the carbon-neutral concrete wheelhouse in the past number of years, many of them are out of reach for one reason or another. Nmai remains hopeful that through research and validation, these alternative sources of concrete can become widespread and used all over the world.

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