Q: I’ve heard that concrete masonry structures have low embodied carbon, is this true? Just checking…
-Green Washing Always Rejectable
Dear GWAR:
Yes, this IS true, but not all concrete has the same embodied carbon. Concrete Masonry Units (CMU) are made with dry-cast concrete (zero-slump) which use less water and cement than poured-in-place concrete (typically referred to as wet-cast concrete). The unique structure of dry-cast concrete enables increased rates of carbon dioxide sequestration (aka carbon uptake, carbonation, limestone mineralization), and at a much faster rate when compared with wet-cast concrete. In addition to CMU assemblies using less cement and sequestering more carbon dioxide, they also use less volume of concrete due to their cores or voids. We can capture all 3 of these factors which drastically lower embodied carbon by looking at embodied carbon cradle-to-gate Life Cycle Analysis (LCA) studies.
In recent industry research incorporating CMU specific sequestration testing, several wall assemblies were compared including a CMU cavity wall with architectural CMU veneer, insulated concrete forms (ICF) with clay brick veneer, tilt-up with thin brick veneer, wood frame with metal panel, and steel frame with metal panel. A1-A3 (cradle to gate) was considered, which is generally where concrete structures are the most embodied carbon intensive. Durability, resilience and low maintenance in the use phase of the building (which is where concrete shines) was not part of the study.
Drumroll please… At the gate, CMU structures are closer in embodied carbon to the framed assemblies than they are to the other concrete assemblies!
2 years into the use phase, the concrete block cavity wall has similar embodied carbon compared to the framed assemblies. 20 years into the use phase, it is projected that the concrete block cavity wall will have lower embodied carbon when compared to the framed assemblies. And that’s the Beauty of Block.
Heidi Jandris grew up immersed in all things concrete block. As a kid she helped her dad build block walls and as an adult worked by his side as a welder. She received a Bachelor of Architecture degree from Pratt Institute and a Masters of Sustainable Building Systems degree from Northeastern University’s College of Engineering. She is part of the 3rd generation of her family’s business. She provides technical services to the design community while researching and implementing ways to improve the efficiency and lower the environmental impacts of their products.
