Supplementary cementitious materials (SCMs) have become an integral part of modern concrete mixes. SCMs are materials that, when used in conjunction with portland cement or blended cements, contribute to the properties of hardened concrete through hydraulic and/or pozzolanic activity .
SCMs are commonly by-products of other industries that can replace the cement portion of concrete, thereby offering sustainability advantages. They further contribute to the concrete sustainability by enhancing concrete durability and general performance. Most common SCMs include fly ash, slag cement, silica fume, and natural pozzolans (e.g., metakaolin).
But what happens when we add CO2 to SCMs with the use of CarbonCure Technologies?
How does CarbonCure interact with the SCMs?
CarbonCure Technologies (CCT) has been used in thousands of different ready-mix concrete mixes across North/South America, Europe, Asia, and Oceania. Concrete mixes made with traditional Ordinary Portland Cement and commonly used SCMs such as fly ash and blast furnace slag are being placed every day.
As such, there are no incompatibility issues when using CCT with other SCMs in ready-mix concrete as the injected CO2 mainly reacts with the calcium-silicate phases of the cement.
Can CCT significantly reduce the amount of embodied carbon the same way SCMs do?
CCT is not a replacement for SCMs, it is complementary to SCMs to further reduce the concrete carbon footprint. CCT is not meant to be the only carbon footprint reduction method to use in concrete.
A CarbonCure producer recently produced a concrete mix that includes Class C fly ash at a cement replacement level of 25% by mass. When CCT was added into the mix, the cement content could be further reduced by an additional 3.2% without compromising the strength properties (in fact, it slightly improved the 28-day compressive strength).
This is due mainly to an increased cement efficiency of the concrete mix (i.e., strength/cement content ratio) caused by the formation of calcium carbonate (calcite) nanoparticles from the CO2 mineralization .
|Metric||Units||Reference Mix||CarbonCure Mix||Difference|
|Type I/II||kg/m3 (lb/yd3)||228 (385)||221 (373)||-3.2%|
|Class C Fly Ash||kg/m3 (lb/yd3)||78 (132)||74 (124)||-6.1%|
|CO2||kg/m3 (lb/yd3)||-||464 (12)|
|Average 28-day Strength||MPa (psi)||33.2 (4815)||34.6 (5025)||+4.3%|
|Cement Efficiency||MPa∙kg-1∙m3 |
|0.15 (12.51)||0.16 (13.47)||+7.7%|
Has CCT been used with high SCMs concrete mixes?
A few examples of high SCMs mixes with the CarbonCure ready-mix technology are mixes used include concrete mixes that include 40% of slag cement, and ternary blends that include up to 70% fly ash and slag in their concrete mixes.
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1. Lothenbach, B., Scrivener, K., & Hooton, R. D. (2011). Supplementary cementitious materials. Cement and concrete research, 41(12), 1244-1256.
2. Monkman, S., Kenward, P. A., Dipple, G., MacDonald, M., & Raudsepp, M. (2018). Activation of cement hydration with carbon dioxide. Journal of Sustainable Cement-Based Materials, 7(3), 160-181.