Curious to know how folks have been creating baselines for concrete, against which you calculation the impact reductions in your project’s concrete mixes. The NRMCA 2016 and 2019 benchmarks are great resources, but they’re limited in that they don’t work well for high-early strength mixes, shotcrete, and self-consolidating concrete. Moreover, they don’t go beyond 8000 psi @ 28 days. How have people been benchmarking these mixes? Perhaps filtering EC3 for your region and strength and then finding an EPD aligning with ‘achievable’ or ‘conservative’ GWP?
Hi Prateek,
Have you use the ZGF’s Concrete LCA Tool Update Version 3.0., contact @baha.sadreddin , he should be able to provide a copy of the tool to you. You should be able to do 8000 psi mixes although I have never used it for that strength.
I have used the EC3 tool to find mixes within my region for the specific strength, the issue is that you normally don’t have the formula for the mix. I have contacted some concrete producers in my area to request the SCMs in the mix, but that is pretty much it, I don’t have anything else such as W/C ratios. But I have used the EC3 Tool to give a max threshold based on the conservative value for the area.
I will a try to the ZGF calculator and see how close you get to the conservative value from the EC3 Tool.
Prateek
Last week I had an interesting phone conversation with Daniel Green at BASF regarding EPDs for concrete. As the NRMCA has am industry EPD that covers most if not all of the ready mix plants in the US. In speaking with Daniel, BASF can provide ways of reducing the carbon foot print for your project by 30 to 70 percent. It may be advantageous to contact Daniel at daniel.r.green at BASF.com for further information.
Good Luck
Tom
Victoria, I have used the ZGF Tool. It replicates the NRMCA 2016 and 2019 Benchmark studies, which don’t go beyond 8000 psi and don’t call out shotcrete, high-early strength mixes or self-consolidating concrete. I’m looking for a good regional baseline for these types of mixes - whether it’s mix design quantities or EPDs.
For anything higher strength psi I would use the highest reference psi available. Higher strength generally means higher impact, which means it will be harder to show any reduction. If you don’t see a reduction, then just use your actual mix for both baseline and design cases. (This would be true at least in GWP as shown in the study used for the development of the Low Carbon Concrete Code in the Bay Area - this is a screenshot from a webinar, so i don’t have an exact link to the source).
For shotcrete and high-early strength concrete I am also not aware of any regional baselines, so EC3 might be your best bet. High-early by definition has higher cement content so it’s not very carbon-conscious in the first place, since you would normally look to lower your cement content and use SCMs that typically slow the time to strength. In that case I wouldn’t claim any reductions just as in the other scenario, unless someone proves me otherwise. I am not too familiar with shotcrete, so again, better not claim a reduction that claim a bogus one.
All of that makes sense, @Vaclav - thanks a lot! On the topic of high-early strength mixes, however, based on what I’ve heard from Central Concrete - they can still do a CarbonCure + Orca Aggregate + 30% slag mix and reduce cement - which I imagine would be a significant improvement over the industry-standard. I guess I’ll still compare that against the 8000 psi NRMCA benchmark, I won’t be overestimating savings in any case.
In that case you could ask Central Concrete for a “typical” mix data before all the improvements you just mentioned and provide LCA info for both. Include the explanation of differences as you just described as well. Assuming all that changes is the mix designs and no upstream data, that should be a valid comparison.
I think it is a fundamental issue that was not resolved after the recent concrete PCR. We proposed the following solutions to move towards a performance-based assessment that realistically address the functionality of the concrete mixture. The following paragraph is a part of a project report that I wrote about meta-analysis and harmonization of concrete EPDs. “There is an interesting momentum among concrete stakeholders to shift from a prescription-based design to the performance-based design. Considering this momentum, it seems quite relevant and critical to track the EPD results reported through a more comprehensive specification level. One should note that only the 28-day compressive strength (and in few cases 56-day compressive strength) was reported in the published EPDs and the industry benchmarks. Indeed, the 28-day compressive strength might not reflect all the required performance metrics for structural applications. As different design standards and guidelines require different metrics, it seems inaccurate to estimate these performances (e.g. early age strength, flexural strength, workability, and durability) based on the 28-day compressive strength. Therefore, a fair comparison of EPDs for different mix designs selected for a specific structural element, that is exposed to an aggressive environment, may not be viable with the current format. The other example is for concrete pavement that the flexural strength is the main input for the mechanical properties used in pavement design. Therefore, we propose to incorporate at least, the exposure class (according to Table 19.3.1.1 in ACI 318-19- Building Code Requirements for Structural Concrete) for concrete used in buildings as a mandatory performance specification to be reported in EPDs. Also, we propose to include flexural strength, shrinkage, and stiffness (Young’s modulus) as the mandatory specification for EPDs used for concrete pavements. These properties will give a clear apple-to-apple comparison among the other results.”
Just out of interest this paper provides a review of ultra high compressive strength mixes up to 200 MPa that you could put into the ZGF estimator, although there are likely to be some admixtures and mineral additions that might not be accounted for.
I am interested to see if there are carbon savings from using ultra high compressive strength mixes to optimize the structural design and reduce overall material use - in case any structural engineers are reading!
