An additional emerging and futuristic technology is one-celled marine microalgae called coccolithophores that produce calcium carbonate. Most atmospheric CO2 dissolved in seawater is rapidly converted to bicarbonate. Coccolithophores use this bicarbonate to create limestone, which can be a form of carbon capture. It takes 1-2 million acres of open pond systems to grow enough microalgae-producing limestone to meet the demand for cement production in the U.S. — that’s about 90 million tons annually. That seems like a lot, but to put it into perspective, the U.S. uses 100 million acres of land to grow corn, so we would need only 1% of that for the ponds. This research is still being studied at a university level; that’s why it is futuristic. Last year at the National Ready Mix Concrete Association (NRMCA) annual convention, speakers from several universities talked about the potential of this growing technology. This is a good sign that this research is moving forward and that there has been a proof of concept. How do materials like fly ash, slag or alternative binders help reduce carbon emissions in concrete production? Simply put, such materials replace the amount of cement needed. And less cement in a concrete mix right now equals less carbon. Can carbon sequestration methods (e.g., injecting CO2 into concrete) be scaled for widespread use? There are companies out there that will encapsulate CO2, bring it to your plant and inject it into your mix. But there are some drawbacks. The system that is used for CO2 injection must be integrated into every batch plant and they’re going to have to transport the CO2 to the plant. As we discussed, the carbon footprint of concrete right now is measured as the constituents and the transportation of the product to the plant. With current yields of a few percent reduction with injection, and a probable gain of carbon yield in transportation, at best, it zeroes out, and at worst, we’re going the wrong way with putting more trucks on the road. Such implementation has to be assessed on a case‑by‑case basis to best understand if there are sustainability gains to be made. POLICY AND STANDARDS Are there government incentives or policies promoting the use of sustainable concrete? My background is as a structural engineer. I consulted for over 15 years, and in that role, you design by building codes that govern how materials are used. You have the overall international building code, and then you have all the material codes. These codes are based on basic minimums that engineers must follow — codes that we’ve gotten to know and trust through practice and evolution of design. They keep us safe. I’m in favor of bringing sustainability into the code system if it doesn’t compromise good engineering design and decision‑making. Lately, policies have been created and are leading the way for carbon reduction in building materials. Some of these policies do it well, while others handcuff themselves as they only provide one path to achieve sustainability with prescriptive specifications. The best policies provide multiple pathways for carbon reduction, allowing for continued good design practice. A lot of what we’re doing now, policy-wise, is a bridging technique focused on “cradle to gate” carbon reduction, but it can’t be the end all. If you’re going to be truly sustainable, you have to take your blinders off. Sustainability should not be focused just on the front end of material supply and consumption. We should be doing a whole building or project lifecycle assessment (LCA) — when you do that, you’re looking at the project, and thus materials, “cradle to grave” and enveloping the farther reaches of sustainability. CHALLENGES AND OPPORTUNITIES What are the biggest barriers to adopting sustainable concrete at scale (e.g., cost, performance, availability)? I think the biggest problem is people who are very well-meaning are looking for one solution. But there is no silver bullet right now to concrete carbon reduction. When someone asks, “Can you bring in a sample of your low-carbon concrete offering?” I reply, “The sample looks like concrete you already know, and there is rarely a physical tell to indicate it is low carbon. The indication of low-carbon concrete is in the numbers and the data that has been indicated behind its constituents. Concrete is regionally dependent because of the variation of constituents available. What can be done in Oregon is not necessarily what can be done in Minnesota. So as far as barriers, it’s not always cost-prohibited or performance-prohibitive so much as it’s people having a good education and understanding of how regionally dependent concrete is and what is achievable in relation to lower carbon mixes. What opportunities exist for architects and engineers to influence the adoption of sustainable materials? Never shy away from an educational opportunity. As I mentioned before, there are methods being used right now to reduce carbon using SCM materials, but these are regionally dependent. The key is in the specification. That is why I strongly advocate that before you write the specifications, talk to your supplier and see what is achievable. Project owners and designers can come to the table with their carbon and project goals, and the supplier can work to help achieve them. Hold pre-procurement meetings and really dig into your goals and specifications. By working together, we can best achieve holistic sustainability in our built environment. Since 1985 9751 W. Chinden Blvd., Suite 200 Garden City, Idaho 83714 (208) 323-0199 www.ahjengineers.com AHJ ENGINEERS, PC STRUCTURAL CONSULTANTS New Buildings ~ Historic Restoraons ~ BIM/Revit Modeling Peer/Plan Reviews ~ Structural Evaluaons ~ Retaining Walls Seismic Retrofits ~ Remodels ~ Expansions PRESERVING THE PAST, PROTECTING THE FUTURE, PROVIDING i-sn SOLUTIONS EVERY DAY 37
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