Mix It Up Supplementary Cementitious Materials (SCMs)

The document argues that substituting portland cement with SCMs—such as fly ash, ground glass, natural pozzolans, and blast furnace slag—is a cost-effective way to reduce the embodied carbon of concrete. It highlights that up to 40% substitution is possible in the US, potentially saving 27 Mt CO2e per year and reducing emissions for specific applications by up to 80%. However, it notes that supply for some SCMs is geographically constrained or declining due to the phase-out of coal power, suggesting the reclamation of stored fly ash and the use of natural pozzolans as viable future alternatives.

• Substituting cement with SCMs can lead to significant emissions reductions, potentially exceeding 80% for a given application, and could save 27 Mt CO2e per year across the United States based on a maximum substitution rate of 40%.
• The use of SCMs can be cost-competitive, reducing the cost of cement blends by up to $45 per ton, although these savings are highly dependent on the proximity of the concrete producer to the SCM source due to transportation costs.
• ASTM C595 establishes different substitution limits for materials: 15% for limestone, 40% for pozzolans, and 95% for ground granulated blast furnace slag (GGBFS).
• The supply of GGBFS is severely limited geographically, with the remaining blast furnaces located in the Great Lakes region and an economic trucking distance of approximately 300 km.
• While new fly ash production is declining as coal-fired power plants retire, there is a significant opportunity to reclaim approximately 600 Mt of fly ash stored in waste sites over the last 20 years, which could support the 40% substitution rate for 14 years.
• Primary obstacles to the increased adoption of SCMs include prescriptive specifications, industry unfamiliarity with certain options like ground glass or natural pozzolans, and complex supply-side logistics.

APA

RMI (2021). Mix It Up Supplementary Cementitious Materials (SCMs). https://rmi.org/wp-content/uploads/2021/08/ConcreteGuide2.pdf

Chicago

RMI. Mix It Up Supplementary Cementitious Materials (SCMs). 2021. https://rmi.org/wp-content/uploads/2021/08/ConcreteGuide2.pdf.

Wikipedia

{{cite report |author=RMI |title=Mix It Up Supplementary Cementitious Materials (SCMs) |date=July 2021 |url=https://rmi.org/wp-content/uploads/2021/08/ConcreteGuide2.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{rmi2021mix, author = {{RMI}}, title = {{Mix It Up Supplementary Cementitious Materials (SCMs)}}, institution = {RMI}, year = {2021}, month = jul, url = {https://rmi.org/wp-content/uploads/2021/08/ConcreteGuide2.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }