Heat of Hydration 2

[dik]

I'm looking for some material information.

Does anyone know at what temperature, the heat of hydration is detrimental to concrete. I'm not thinking differential temperatures, but just how hot the concrete can get. In addition, is there a strength at which heat of hydration is not a problem, anymore?

The reason being is that concrete gains strength when it is warm (or maybe a little hot) and if the forms can be insulated to capture the heat of hydration, it may promote early strength. Just curious.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[LittleWheels]

The risk from high temperatures during curing is Delayed Ettringite Formation (DEF). The higher the temperature, the higher the risk. Zero risk at 65C, low risk at 70C, high risk at 75C and very high risk at 80C. Most concrete codes have a limiting temperature, usually 70C or so.

This risk is modified by the concrete composition. Replacing cement with GGBS or fly ash, particularly higher percentages, reduces the risk at a specific temperature.

 

[dik]

Thanks for the information. Is there an additive, or different blend of cement, that can be used to minimise DEF?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[LittleWheels]

GGBS or fly ash cement replacements (rather than CEMI) make a noticeable reduction in DEF risk, both because of reduced heat of hydration and because of suppression of DEF for a specific concrete temperature. There are various papers about DEF risk mitigation but I can't lay my hands on any of them right now.

https://link.springer.com/article/10.1007/s12205-017-0642-6

is the sort of thing I am thinking of.

 

[driftLimiter]

@Dik. I use A.M Neville's book 'Properties of Concrete' as a go to for these kind of questions. Its been a little while since I have used it extensively so I don't have a good answer for you off hand, but I thought you might be interested in this reference.

 

[dik]

I was at an ACI Manitoba dinner last night and the discussion was related to determining in-situ strength of concrete. Recording of time and temperature for maturity was one of the methods. I don't know this, but an upcoming issue with concrete may the the very large carbon footprint. There may be a large 'push' for concrete supply based on specific requirements, and not on specific 28 day strength. Rapid curing, with heat of hydration, may be part of the solution.

Cementitious materials is part of the solution... in the last two decades, I've gone from 20% max to 40% max...

drift... I'll see if I can dig up the reference.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[LittleWheels]

I recall reading about some interesting chloride penetration effects from curing at elevated temperatures. There is some evidence that chlorides penetrate hot-cured concrete more rapidly than when it is cured at lower temperatures. I do a fair bit of marine and port work, so mostly focus on chloride resistance for durability. No doubt there are other concrete performance aspects affected, both positively and negatively.

 

[dik]

I suspect a lot of precast concrete girders are heat and steam cured... I wonder if they do anything different.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[bugbus]

Transport for New South Wales:

"The maximum temperature of the concrete during and after the application of heat must not exceed 70°C for all concrete exposure classifications"

Queensland TMR:

"The maximum temperature within the enclosure (steam curing), or the maximum water temperature (hot water curing) shall not exceed 70°C. The maximum temperature at any point within the concrete shall not exceed 80°C at any point during or after the heating or curing process. The internal concrete temperatures shall be measured at the largest cross section for a period of 48 hours after concrete placement or until temperatures have dropped to 5°C below the peak temperature whichever occurs first."

 

[dik]

Thanks...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[LittleWheels]

For reference, virtually all cement specified by the Queensland TMR has a significant minimum fly ash content, hence the high allowable concrete temperature. That is mostly because reactive aggregates are common in Queensland but DEF mitigation is a bonus.

 

[dik]

I suspect there will be numerous changes in concrete mix design in the future to improve it's carbon footprint.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[LittleWheels]

I expect increased use of limestone and pozzolanic cementitious replacements with fly ash gradually reducing as coal-fired power stations shut down.

 

[dik]

That too... and to reduce the use, I suspect there will be a lot of prescriptive specifications. It's all a WAG at this point in time...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[KootK]

I use A.M Neville's book 'Properties of Concrete' as a go to for these kind of questions.

Me too! Neville was actually "local" for me in that he spent a portion of his academic career at the university of Calgary as the engineering department's founding dean (he passed in 2016). He was emeritus during my time buy I lucked out and got to meet him at Mrs. KootK's graduation ceremony (also structural). I was the taker of the photo below. Would you believe that Mrs. KootK didn't even know who he was or why I was making a big deal of it? Yeesh. I should have made her take a photo of Neville and me instead.