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Name:   
Heading: 1.2.1LEED Concrete and Construction
Message:
Has anyone run into any issues regarding LEED credits and concrete? To be more specific, LEED mixes generally use pozzolans which typically decrease the 7 day breaks. Rarely does a specification call for a 7 day strength requirement, but the general industry standard is 70% in 7 days.

We all know how nervous folks can get when they see a low 7 day break. It can significantly impact the schedule of the project as well.

So, my question is, what is the industry's standpoint regarding this issue? What has worked for some of you, and are you seeing similar issues on projects that you are currently working?

Thanks, and I appreciate everyones response.


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Jonathan Harrell


Jonathan,

We work with customers to do exactly what you are describing. The new CEMEX headquarters in Houston is a great example. Baker used a mix-design with fly ash which reduced material costs and earned the project LEED points. They were concerned with the rate of strength gain but by monitoring in-place strength with intelliRock (concrete maturity technology)they found that they were still able to stress PT beams in 18 hours and strip decks 20 hours after placement while using the leaner mix design.

Typically what we find when using intelliRock is that the in-place strength is substantially higher than what is indicated by cylinders. This is due to the heat that is trapped in the placement which accelerates hydration. So even when the rate of strength gain is lower using a lean mix design, you buy that time back by measuring the actual strength of the placement.

Here is a great case study:
http://www.engius.com/web/publications/casestudies/CEMEX%20Baker%20Case%20Study%20090409.pdf

Cheers,
Michael Fox
Engius, LLC
www.engius.com
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Michael Fox


Dont just look at fly-ash (althought that is all I have seen in the last couple of days with a dam using 70% of the binder of it).
Calcium Carbonate Fines, also incombination with GGBS, and high quality OPC will give you excellent demoulding strength and I presume LEED points.
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Boudewijn Piscaer
 
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