Low CO2 concrete curing times

[Fynch]

I'm looking to reduce CO2 in my concrete however I need a concrete that achieves its strength fast.

I've been looking at fly ash, cemfree and Cemex Vurtua however, they all appear to have slower curing times.

Am I missing something? Is there any concretes that are lower CO2 but will achieve a high strength fast?

 

[bones206]

I recently found out about a company that injects recycled CO2 in the concrete mix. Info here:

https://www.carboncure.com/audience/engineers/

 

[dik]

Fly ash, etc. may not give an early strength gain... I would be reluctant to inject CO2 into a concrete mix... might reduce corrosion resistance... look up carbonation.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ron]

agree with dik....carbonation is an issue with rebar corrosion

 

[IDS]

agree with dik....carbonation is an issue with rebar corrosion

Which is probably why that issue is addressed in the documentation at the link provided by bones206.

It's certainly something that needs to be considered, but I don't think we should just dismiss the idea without investigation.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[dik]

reminds me of contractors wanting to add CaCl₂ to concrete mixes in the early days... just speeds things up a tad... I'd like to see the effects of this in a few years... not ready to jump on this bandwagon.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[bones206]

Here's the company's explainer:

CarbonCure's technology involves the introduction of carbon dioxide into concrete as it is being batched and mixed. The CO2 is mineralized in a chemical reaction that occurs alongside the earliest stages of the cement hydration. Subsequent hydration and phase development continue as normal after the CO2 is added. The introduced CO2 converts to a solid CaCO3 mineral. The mineralization reaction central to CO2 utilization takes place within the first few minutes of hydration, whereas weathering (atmospheric) carbonation takes place in concrete in service over long time scales (e.g., months and years). The latter reaction sees CO2 from the atmosphere react with cement hydration phases present in mature concrete which compromises durability. The CO2 utilization process involves a reaction between deliberately added CO2 and the earliest forming hydration phases and/or clinker phases in concrete that is in the fresh state. The in situ development of calcium carbonate during mixing can improve performance without experiencing the negative effects of atmospheric carbonation.

Btw I don't think curing time is affected significantly, based on their literature.

What's driving the need to reduce CO2? Project requirement or personal decision? Either way, I am all for it!

 

[dik]

If you believe in climate change and human CO₂ effects, with the high CO₂in the atmosphere, they are trying to capture it and 'permanently' remove it from the system... storing it in concrete structures.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ron]

A few thoughts....

1. CarbonCure is selling a system. Their info has a lot of marketing in it and a couple of statements/premises I find questionable.
2. Converting the CO2 to CaCO3 means that Calcium is being robbed from the cement. That's not good. Calcium is one of the necessary components of the hydration process.
3. They mention a "clinker" phase in concrete. Concrete doesn't have a clinker phase. Cement production has a clinker phase before grinding, but not concrete.
4. Calcium carbonate formation within concrete will leach out as moisture moves in and out of the concrete, leaving efflorescence on the surface. This is something we try to prevent in concrete and other cementitious products, not something we want to promote as a feature.

I certainly have nothing against innovation and progress; however, it must be reasoned and observed in a longer term process to assess its impact to durability and serviceability. dik mentioned the calcium chloride fiasco of years ago. It was used a lot in a short time of a few years before its detrimental properties were discovered, resulting in millions of dollars in repairs.

 

[STrctPono]

I have been to an all day seminar put on by our State DOT which hosted CarbonCure. Our City/State actually became the first municipality in the Country to implement a carbon mineralization requirement in concrete for all State and City funded projects. I have mixed feelings. I appreciate what they are trying to do but I am afraid that in order to ride the publicity wave, some of the practices that are actually being implemented just don't make sense. I question the actual use of post-industrial CO2 for the production of concrete. We have no coal-fired power plants in my area producing massive amounts of CO2. Also, I have questions about the energy that goes into capturing the CO2, transporting it, and injecting it. All of this is energy intensive and offsets the benefits of sequestering carbon dioxide.

What's driving the need to reduce CO2? Project requirement or personal decision? Either way, I am all for it!

In the public sector, it's easy. The State or City would mandate it. In the private industry it's a bit trickier, however, with the creation of LEED points and all it's not going to be too difficult for it to find it's way in to the next residential condominium. In my City, the Ready Mix companies are fighting it tooth and nail but it appears that they lost the fight. Only 1 supplier got on board early and is actually able to supply it.

The way that we write our specifications, there are two ways around it.... incorporate supplementary cementitious materials (thus reducing your cement use) and/or use less cement but add strength enhancing admixtures. One issue I take with the cement industry in general is that most concrete mixes use WAY too much cement anyway. Engineers limit the W/C ratio, so in response Ready Mix Suppliers up the Cement to 800 lbs/cyd in order to satisfy. Most untrained Engineers would be none the wiser that they are adding 360 lbs of water to the mix!

BTW, dik and Ron, you better believe that every Engineer's hand in the room shot up and said "What about Carbonation!?" Quite frankly, 99% of us Engineers know squat about chemistry and have no right questioning something we really don't understand. Needless to say, that problem has been researched and was addressed. In short, it is a non-issue.

 

[dik]

have no right questioning something we really don't understand

I've done that nearly all my life... As a kid, it got me into trouble more times than I can recall.
It's my way of learning...

I'm not a chemist, and don't pretend to be... but have a little bit of a handle on chemistry... enough to keep me out of trouble... the same way I've known about carbonation for the last 30 or 40 years, before it became trendy... I think it was the late John Bickley that introduced me to it about 40 years back with reference to parking garage corrosion; he was way ahead of his time. I also have a bit of a heads up on corrosion issues and also coating systems... both touch on chemistry... enough to keep me out of trouble. I'm also aware of why it is being considered, and the consequences of CO₂ in the atmosphere... The object is not to contain it... but to quit the production of it... storing it gives the impression that we can continue to generate the stuff (chemistry term).

Rant over...



Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Fynch]

Okay interesting.

But when about the Cemex Vurtua range using a geopolymer binder? What are thoughts on this?

Or Cemfree using GGBS? Could additives increase curing times?

 

[Ron]

@dik....thank you for the mention of John Bickley. One of the most knowledgeable concrete experts ever. I learned a lot from him in my time with Trow in the 80's.

Innovation sometimes takes a lot of time. This is particularly true of construction materials that are intended to last for 40 or 50 years and more...all while performing properly and being durable and serviceable. In my career I've seen innovations pop up and go away. Some may recall that in the 70's and 80's new roofing materials were being touted almost monthly. The salesmen would say things like they would easily last 20 years and beyond...all with no tried evidence to support them. Some stuck around, some died out completely and some got modified when they found their limitations. All results were good for the innovative process, but sometimes not so good for the end user.

 

[dik]

Me too... He was involved with only a few projects I did, but he's well remembered, and I too learned a bunch... With the parking garages that RJC did, he (aka Trow) was a welcomed consultant.

As far as GGSB goes... I've not needed to use it. It does hold great promise as a means of encapsulating CO₂. It and several similar types of approaches of a similar nature will be sorely needed in the future. My first inkling of capture concrete was an article a year or so back on a project in one of the Scandanavian countries. I thought, at the time, it was a trivial solution... a bandaid on a major haemorrhage; I guess every little bit helps.

Other than cursory information, I'm not familiar with GGSB other than it is a fly ash like substitute, I think classed as a mineral admixture. It can be used for some very high strength concrete mix designs, moreso than other fly ash like products. It has very good resistance to sulphate and chloride ions... and the heat of hydration is slightly greater than normal fly ashes, but less than PCC. As expected, strength gain is retarded a bit. That's about the sum of the information. I'm not sure of the effect of the geopolymer binder is, other than maybe help improve the CO₂ encapsulation.

I do like 'weird' products and try to incorporate them, and if I was actively involved with concrete, I'd be doing some research on it. I probably used polypropylene fibers for the first time in the province... they first came out about 50 years back and Qualico had a concrete apron that was subject to frontend loader activity and I needed something to 'toughen' the slab... I was aware that improvements were to the cement gel and that real reinforcing was needed, too. Likely did the first ICF building in the province about 50 years back... a three storey walkup in Dauphin... a product called FoamForm.


Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[ACtrafficengr]

I saw a presentation last week about type 1L cement. It might answer the OP's question. It has 5 - 15% limestone ground in with the clinker, which supposedly helps with nucleation and particle packing, and reduces CO₂ produced by 10%.

http://onlinepubs.trb.org/onlinepubs/webinars/121113.pdf

https://www.cement.org/sustainability/portland-limestone-cement

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[Ron]

GGSB is used quite a bit in my area. It results in slower strength gain but otherwise has no significant negative effect on the concrete.

 

[Fynch]

Thank you everyone.... Some things to have a think about!