Looking for low carbon concrete case studies

I don’t have an immediate example at hand of a 30% SCM mix, but I will share how we are approaching low carbon concrete: The approach we are taking is to set a GWP reduction as a performance target for the concrete mixes, and then our spec and structural notes require the GC to meet the GWP reduction through whatever combination of SCMs, cement types, admixtures, etc will achieve the target. We felt that would provide the most flexibility with supply chain and pricing fluctuations creating a lot of uncertainty. We also encourage our structural engineer to extend the strength targets from 28 days to 56 days, or whatever they are comfortable with, which also gives the concrete supplier flexibility to reduce cement content. Using Type 1L cement can achieve as much, or more, reduction in GWP as using a high percentage of SCMs. Example of what that looks like from a recent project: From the specification: 2.01 Performance Criteria A. Carbon Footprint Reduction: Provide concrete mix designs with EPDs showing maximum Global Warming Potential (GWP) as listed below: 1. Strength 3,000 psi: Maximum: 208 kilograms of CO2 embodied/cubic yard. (35% reduction from 2019 Carbon Leadership Forum baseline). 2. Strength 4,000 psi: Maximum 258 kilograms of CO2 embodied/cubic yard. (35% reduction from 2019 Carbon Leadership Forum baseline). 3. Strength 4,500 psi: Maximum: 317 kilograms of CO2 embodied/cubic yard. (35% reduction from 2019 Carbon Leadership Forum Benchmark: baseline). 4. Strength 6,000 psi: Maximum 256 kilograms of CO2 embodied/cubic yard. (50% reduction from 2019 Carbon Leadership Forum baseline). B. Submit mix designs for review using Type 1L cement, increased fly ash and blast furnace slag content, carbon-reducing admixtures and adjusted water-cement ratios, as needed to meet the carbon reduction targets. Conform to mix design requirements shown on General Structural Notes.   General structural notes: TYPE OF CONSTRUCTION                             MIN. 28 DAY STRENGTH (U.O.N.)                   EXPOSURE CLASSES                                                                  (f'c)                                                              (ACI 318-14 TABLES 19.3.1.1 AND 19.3.2.1) A. CONCRETE EXPOSED TO WEATHER            4,500 PSI                                                     (F1, S0, W0, C1) B. CONCRETE EXPOSED TO EARTH                6,000 PSI                                                     (F0, S0, W0, C1)     (FOUNDATIONS, BASEMENT WALLS, ETC.) (AT 56 DAYS) C. ALL OTHER CONCRETE                            4,000 PSI                                                      (F0, S0, W0, C0)   Mix Design On a different project but one with similar specification, the submitted mix design for footings is as follows. (You can look this mix up on EC3 using the mix design number) Mix Design: P3C55414 Strength: 3500psi Mix design GWP: 184 kgCO2e/yd3 Reduction from CLF baseline: 54% S.S.D. Weights per Cubic Yard Portland Cement Type 1L 440 lb Fly Ash (Slag)* 77 lb Coarse Aggregate, ¾” 10.67 cu. ft. Coarse Aggregate, ⅜” 0.97 cu. ft. Fine Aggregate 7.76 cu. ft. Water Reducer, Type A 1-40 oz Water 270 lb *Conforms to ASTM C-618 – 17a (ASTM C-989) Fly Ash or Slag may be used depending on availability

I have a recent project in Columbia, Maryland where we used 39% slag and achieved a roughly 15% reduction from the regional average compared to the NRMCA LCA performed by the Athena Sustainablity Institute (my current preferred standard baseline). The concrete was set about 4 months ago and so far so good. I've asked around for other examples and hope to provide more here. Two thing to note. The NRMCA LCA has performance metrix for 30 and 40% SCMs. Also, I encourage our engineers to elaborate on the testing expectations to help insure the structural performance of the mix. 

Meta is using AI to create low-carbon concrete for its data centers https://www.newscientist.com/article/2317122-meta-is-using-ai-to-create-low-carbon-concrete-for-its-data-centres/#:~:text=Facebook%E2%80%99s%20parent%20company%2C%20Meta%2C%20has%20used%20AI%20to,already%20using%20it%20in%20its%20latest%20data%20centre. [https://images.newscientist.com/wp-content/uploads/2022/04/27172342/SEI_100915202.jpg] Meta is using AI to create low-carbon concrete for its data centres Basic concrete is a mix of cement and an aggregate such as gravel, mixed with water. Commercial concrete can contain dozens or even hundreds of ingredients to achieve a desired strength or durability. www.newscientist.com

We have several projects that use mixes above 30%. The reality is that some mixes that are ok with longer cure times (often foundations, shear walls, seismic reinforcement, some slabs) because they will not be loaded fully for some time. So with a project that has extensive foundations the project average can be fairly high. We have one project where the average (per volume) is 42% better than the NRMCA baseline – it has extensive foundations. Like Kristian, we have standard language. We most often require 30% lower GWP than the NRMCA baseline report and have found that GCs can meet that in many markets in the US. The Spec language primarily lives in Div 01 8113, but we also ask the Structural engineer to modify their mix requirements and Div 03 language to allow for longer cure times (as has already been said by others on this thread). Also, many places in the US are moving to Type 1L as a standard, which lowers GWP as well. One of the tricks is that different aggregates in different parts of the US require more or less cement, so sometimes aggregates are imported to lower GWP. We also had one Super recently that wanted to avoid vibrating the concrete around the rebar and so they picked a higher-GWP mix with more water and cement. Because our language required a 30% reduction, they had to then balance the higher GWP mix against other mixes, and ended up only with the higher GWP mix at the lowest floors where the rebar was most dense. It was great to see that our Specs were flexible enough to accommodate this unexpected request yet maintain rigor. We haven’t published any of this but I can share more data with you if interested. -Kjell Fro

One of the tricks is that different aggregates in different parts of the US require more or less cement

This was fascinating and eye-opening to learn. It really is an important factor. Our projects in Portland have had a harder time meeting the targets than our projects in Seattle, and one of the reasons explained by the Portland ready-mix suppliers is there's a difference in aggregate between the two areas, and the Portland aggregates require more cement to achieve the same strengths.

Another example of AI learning and concrete… this serendipitously popped up in a totally unrelated email search shortly after your note on Meta and AI came through. I took it as sign form the universe to share. https://news.mit.edu/2021/more-sustainable-concrete-machine-learning-1207 Heather DeGrella AIA, LEED AP BD+C, Fitwel Ambassador, EAC-PS, | (she / her / hers) Associate Principal | Sustainable Design Director [cid:opsislogo2021_13a53c65-c652-4f53-a86d-657f2f0f9b85.png] Architecture, Interiors & Planning 920 NW 17th Avenue, Portland, OR 97209 o 503.525.9511 d 503.943.6228 w opsisarch.com F

Bryna, Allow me to connect you with my predecessor at Vanderweil, Suzanne Robinson, who is now with LeMessurier (structural engineer in Boston) focused on the embodied carbon of structural design. She shared a case study her firm worked on that’s in construction now in Boston. To date, it’s the largest replacement rate for portland cement in the Boston area - “the project employed concrete with portland cement replacement rates of up to 63%, the highest ever used in Boston for this type of application. This yielded some mixes with a nearly 30% reduction in embodied carbon.” Full article: https://www.structuremag.org/?p=20625 You can follow up with her with questions at srobinson@lemessurier.com Isn’t it about time we have a sustainable structural design leader group now? Best, Patrick Murphy, PE, LEED AP BD+C, CPHC Associate Principal | Director of Sustainable Design R.G. Vanderweil Engineers, LLP T 617.956.4804 | C 607.621.8047 www.vanderweil.com [cid:image001.gif@01D8BBB5.26ABFD30] [cid:image002.gif@01D8BBB5.26ABFD30] [cid:image003.gif@01D8BBB5.26ABFD30] [cid:image004.jpg@01D8BBB5.26ABFD30] From: Bry