College - Author 1
College of Architecture and Environmental Design
Department - Author 1
Architectural Engineering Department
Degree Name - Author 1
BS in Architectural Engineering
College - Author 2
College of Architecture and Environmental Design
Department - Author 2
Architectural Engineering Department
Degree - Author 2
BS in Architectural Engineering
Date
6-2025
Primary Advisor
Cole McDaniel, College of Architecture and Environmental Design, Architectural Engineering Department
Abstract/Summary
As greenhouse gas emissions continue to rise, many in the construction industry are looking for sustainable solutions to reduce its carbon footprint. One of the biggest contributors to atmospheric CO2 comes from cement production. In 2023, researchers at MIT explored ways to enhance concrete’s natural ability to act as a carbon sink. Concrete does this unassisted through a chemical reaction called carbonation, by which atmospheric carbon bonds to key components in cement. The researchers at MIT proposed a process of early-stage forced carbonation, which can be induced by the addition of NaHCO3 into a standard concrete mix. Sodium bicarbonate, or baking soda, allows atmospheric carbon to be converted into a mix of calcite, C-S-H, and disordered calcium carbonate. According to the researchers, this additional chemical process does not compromise cement’s structural integrity. The team tested samples with 0, 5, 10, 15, and 20% sodium bicarbonate to portland cement by weight and found that the control sample slightly outperformed the carbonated solutions, but not by a statistically significant margin in terms of its structural integrity. Unlike cement, concrete is a mixture of coarse and fine aggregates, water, and cement, which acts as the binder. Key components in its construction are workability, how easily it can be poured into set shapes with sufficient time to ensure there aren’t any voids after it is poured, and its durability in terms of its compressive strength. While the research team at MIT claimed the hardness of the alternative cement mixture was comparable to a standard mix, hardness and compressive strength are fundamentally different measures, with hardness having less relevance to performance as a structural material. Likewise, the team only measured up to 7 days, while concrete strength, per ASTM standards, is measured at the 28 day mark. While the published research presented a more environmentally friendly alternative to a 5 standard cement mix, it also failed to explore the key physical properties that are crucial to its widespread adoption in the construction industry. To research these properties, a standard concrete mix design was substituted with 0, 10 and 20% cement-to-baking soda percentages by weight and loaded in a Test Mark machine to determine its compressive strength at 7 and 28 days, in addition to its tensile strength at 28 days. Tests were conducted in accordance with the established industry standards for testing the behavior of concrete, outlined in ASTM C39 and C496. These results were then compared to standard to determine the viability of sodium bicarbonate as a potential admixture in the construction industry.
URL: https://digitalcommons.calpoly.edu/arcesp/224