Open Access
https://doi.org/10.4322/2026360255501
Craig Walloch(a), Pranav Pradeep Kumar(b), Nicholas Lang(a), Randolph Kirchain(b), Hessam Azarijafari(b)
(a) Concrete Masonry and Hardscapes Association (CMHA), Herndon, VA, United States
(b) MIT Concrete Sustainability Hub (CSHub), Massachusetts Institute of Technology, Cambridge, MA, United States

ABSTRACT
Accurate measurement and quantification of the natural carbon uptake of dry-cast manufactured concrete products is crucial for assessing its comprehensive environmental impact. Test protocols for measuring the carbon uptake in manufactured dry-cast concrete products were previously developed with the results on the amount and rate of uptake of nine sets of concrete masonry units (CMU) stored in exposed outdoor conditions from 1 to 6 months of age reported. This paper extends the previous analysis on the same nine sets of units stored in exposed outdoor conditions to 3 years. Moreover, this study compares the findings from the previous nine sets to the test results of two new sets of units stored in sheltered indoor conditions for 2 years. Furthermore, experimental tests using crushed samples of all eleven sets, exposed to the atmospheric conditions, provide an estimate of the maximum carbon uptake potential for dry-cast concrete. The results demonstrate that initial drying conditions during sample preparation play a crucial role in carbon uptake for dry-cast CMUs. However, this effect was not observed at 91 and 182 days, reflecting that the residual moisture’s influence faded over time. Additionally, crushed CMU samples reached a maximum practical limit of approximately 53% of the calcination carbon emission potential after four months of exposure. Following a logarithmic behavior, an empirical model is proposed to effectively capture the observed carbon uptake trends for the two exposure conditions, aligning with the deceleration of carbon uptake over time due to pore blocking and the limited availability of reactive phases.

Keywords: carbon uptake modeling, carbon uptake potential, CO2 uptake modeling, concrete masonry unit (CMU), dry-cast, uptake