Over the last several years, we have put significant effort into refining our structures to be more efficient from a sustainability standpoint. This is a topic we’ve explored extensively during our On Track Series. Whether it is working with architects and owners early to reduce or eliminate the need for transfer slabs, pushing towards post-tensioned slabs to lighten up the structure, or running through several iterations of footing calculations to determine the best combination of concrete strength and footing depth, this is something we are constantly thinking about. But what else can we do to improve the sustainability metrics of your projects?

Well… we can be more patient. Patience is a virtue, and it is sustainable! Historically, standard practice relies on 28-day concrete mixes for all elements. Reaching this strength in 28-days requires higher cement content – and cement is the true culprit in concrete when it comes to emissions.

Supplementary Cementitious Materials (SCMs) are lower-carbon minerals which can be added to a concrete mix to replace cement and therefore reduce the Global Warming Potential (GWP) of a given concrete mix. The only drawback of SCMs is that they will delay the strength gain.

This may be a problem from a scheduling standpoint for slabs, where we need to quickly drop the forms to maintain schedule – but most structural elements won’t experience full design loads for months after construction. Footings and columns won’t carry their full weight until the structure is complete, and core or shear walls may never reach their design load unless a major earthquake occurs (despite last week’s minor earthquake, the probability of a design-level event in any given year is low). These structural elements can wait, so why not maximize the use of SCM’s?

At Glotman Simpson, we are rethinking concrete specifications to lower environmental impact without affecting cost or construction schedules. Our updated specifications set maximum GWP limits and eliminate strict “28-Day Strength” requirements, allowing or requiring 56- and 91-day mixes where early strength isn’t needed. Throughout the development of these specifications, we collaborated closely with local suppliers to ensure that these requirements are easily achievable without impacting cost or availability. With these small, yet deliberate, tweaks to the specifications – and ultimately by being a little more patient – we can make a meaningful impact on the projects overall environmental impact. We didn’t just stop at concrete; reinforcing steel, concrete block unit masonry, and structural steel all play a significant role in the embodied carbon of the base building, so we have set GWP guidance for those too. Please let us know if you’d like us to incorporate these specifications on your next project.

Written by Marcus Monk

Together, we can contribute to a more sustainable built environment. If you are interested in sustainability and would like to discuss any of the topics in this article, please get in touch with us at [email protected]