Hello,
For one of our LEED projects (50-storey mixed use tower), the full structure will be concrete (slabs and columns). Nearly 38,000 cubic meters of concrete will be used.
Some concrete elements will require high strength concrete (up to 80 MPa). The contractor is using additives such as fly ash, slag, and silica fume to replace nearly 20% of the cement used in this concrete, which directly corresponds to 20% reduction in CO2 emissions resulting from the manufacturing of cement (nearly 1 ton of CO2 is produces for each ton of cement). Note that the above technology is the first in the project's country.
Do you think we can claim an ID credit for the above? I know we must verify with the USGBC, but I was wondering whether anyone has previous experience with something similar.
Thanks!
Robert Phinney
Director, Sustainable Design SolutionsHDR
26 thumbs up
June 26, 2013 - 12:19 pm
I do not have direct experience, I am sorry, but it got me thinking about a potential issue that you may need to address or which may help answer the question. The strategy may reduce the CO2 produced int he manufacture of the concrete, but those addatives are a direct result of other processes taht emit high levels of CO2. Do you think the emmissions saved from the concrete strategy will offset the CO2 that results int he production of the laternate raw materials - relative to using more traditional materials?
Joseph Ford, AIA
ArchitectRSP Architects Ltd.
17 thumbs up
June 26, 2013 - 12:33 pm
No direct experience either but I think that what you describe is very unlikely to succeed as an ID credit. You will already be deriving some sustainable value for the cementitious materials under the MR credits so that undermines the case for an Innovation point.
It's also worth mentioning that there is a recognized ID strategy of using 40% or greater fly ash, slag or fume. I'm not sure if that is achievable in your locale but 40% for structural concrete is not difficult to achieve where I work in the US. Even if you can't get to 40% getting above 20% or 30% will go a long way to maxing out your MR points and/or meeting the Exemplary Performance threshold.
Maya Karkour
EcoConsulting872 thumbs up
June 27, 2013 - 2:29 am
Thank you for your comments, much appreciated.
Robert, the fly ash / slag is a waste product resulting from industrial processes (related to electricity power plants, if i'm not mistaken). Therefore, these products are not manufactured specifically to be used as concrete additives, so the CO2 will be produced in all cases.
Joseph, regarding the MR credits, the project won't count these materials under MR Credits 3, 4, or 5 (I don't think they're too significant by cost). Thanks for mentioning the 40% threshold ID Strategy (most probably not achievable for structural concrete as you said) - I think this rules out my scenario.
Robert Phinney
Director, Sustainable Design SolutionsHDR
26 thumbs up
June 27, 2013 - 11:11 am
I fully understand the source of the flyash and slag, and i am not saying that there will not be a CO2 advantage to your strategy - it is certainly a good one in many other ways. However, i am just cautioning you that if you are seeking credit for a reduction in embodied carbon, i find it highly unlikely that you can choose within the life-cycle where you want to compare. Embodied carbon is typically looked at through the whole life-cycle, and flyash and slag still have a carbon footprint associated with them whether they are biproducts or not.
I can see the argument that coal fired plants (the source of the material) could be given credibility over renewable production if an advatage is given to the accidental biproduct from a carbon reduction standpoint.
Again, i am not saying that you are going to fail (i have not run the calculations myself), just that be careful about limiting your definition of life-cycle to potentially inflate the benefits of one portion of the material's overall life-cycle. If you choose to pursue, i would certainly be interested in your findings if you will share with the group.
Joseph Ford, AIA
ArchitectRSP Architects Ltd.
17 thumbs up
June 27, 2013 - 5:34 pm
Omar - I highly recommend you reconsider including the concrete in your MR credits – if your whole structural frame and slabs are concrete this is going to be a significant percentage of your construction cost. Note that for MRc4 you can calculate for cementitious materials only so you will net a much higher percentage than you would by calculating the cement as a percentage weight of the whole concrete mix. Review the section “Supplementary Cementitious Materials” under MRc4 in the Reference Guide.
My experience is that cementitious materials constitute about half of the total cost of concrete. So, if 20% of that is recycled content it will be a decent contribution to the MR credits.
To clarify my earlier comment: 40% fly ash mixes are NOT difficult to use in structural applications in my region of the US. However – if it is a novel use in the project country it definitely could be an issue. I started using 20% mixes in the early-‘00s. No problems with the material itself, but the initial setting and curing properties differ from 100% Portland cement and we got some flawed installations from contractors who were unfamiliar with the material.