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Mass concrete

Mass concrete

Mass concrete

(OP)
DEAR Concrete Experts,
Mass concrete pours are planned with C60 CYLINDER strength mix with 30% Flyash and 7% microsilica. The specs calls for ACI 301 limits on temperatures (70 Deg C max peak internal temp & 20 Deg C differential). A mock up cube 2mx2mx2m was casted during winter season and fresh concrete temp = 20 deg C. The thermal readings achieved the temp limits. (69 Deg C and 17 deg C) and the mix was approved.

Now, we are in summer season where ambient temps are above 40 deg C and adding 80-90% of ice flakes to the mix but fresh temps are not reduced below 26-27 deg C. Other than using ice, aggregates are shaded to reduce the fresh concrete temp.

On actual rafts with thicknesses 3-4 meters, the above mix in hot weather will exceed the 70 Deg C limit. So, we proposed ACI 201.2R16 that allows peak concrete temp upto 85 Deg C IF flyash and microsilica are used but the proposal was not approved.
Also, the raft thickness has proportional influence on peak core temperatures.

Mix has 520 Kgs of total cementitious material @ 0.3 W/C

What are your thoughts on ACI 201.2r16 recommendations that allows peak temps up to 85 deg C if the mix has flyash atleast 25% and 5%microsilica? And, other than using GGBFS, what are other options to achieve ACI 301 temp limits, for a high strength mix as 60 Mpa and pouring in a very hot weather area of the world.

RE: Mass concrete

(OP)
ACI 301 Section 8 on "Mass Concrete" specifies 70 Deg C peak core temperature and differential temp as 20 Deg C without specifying if the mix contains pozzolans or no. It could be talking about 100% portland cement mix that is more susceptible to thermal reactions and higher evolution of heat.
While ACI 201.2R16 clearly states that if prevention is taken by using certain proportions of flyash and microsilica, a higher core temperatures are allowed without the risk of DEF related issues, when it is unavoidable to achieve below 70 Deg C.

Your valuable thoughts please

RE: Mass concrete

Quote:

So, we proposed ACI 201.2R16 that allows peak concrete temp up to 85 Deg C IF flyash and microsilica are used but the proposal was not approved.

Was "Class F" fly ash specified in the mix design submitted, the post does not say? Not all fly ash is suitable for use in concrete.

If Class F was specified, instead of using fly ash and microsilica, resubmit the proposal with another mix design chosen from the several options allowed by ACI 201.2R16. Perhaps just leaving the microsilica out and using >25% Class F fly ash, or >35% Class C fly ash will be accepted... some Owners have preferences regardless of what a spec allows.

RE: Mass concrete

(OP)
@SlideRuleEra thanks
Flyash Type F is used. Microsilica was used for below reasons,
1. durability requirements in terms of RCP, water permeability
2. ACI 201.2R16 specifies microsilica (min 5%) to be used in combination with flyash(min 25%). The table is attached in my posts.
3. strengths are specified at 28 days (not later ages).

RE: Mass concrete

Can you do a different mix? Can you increase the flyash? How large is your aggregate? and how large can your aggregate be?

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

-Dik

RE: Mass concrete

(OP)
@dik thanks
We can do a different mix with GGBFS but it will take time for testing, approvals and rafts are ready to pour. so we dont have time for a new mix approval.
Flyash increase will not help in achieving below 70 Deg C because of high strength mix, and large depths (3.5meters avg).
Max aggregate of aggregate is 20mm and it can be only this large as no larger size available in market.

The big question is weather ACI 301 limit of 70 Deg C is when using normal OPC concrete or pozzolan concrete? ACI 201.2R16 clearly says that when it is practically difficult to achieve below 70 Deg C, preventive action should be taken by using pozzolons in the mix like ggbfs, flyash, microsilica and that will modify the risk of DEF and core temps can go upto max 85 Deg C.



RE: Mass concrete

Toshiba2023 - Seems like you have done everything correctly. If your Client is "reasonable", I am going to tell you how to get approval, and will not be with some "special" technical solution:

I carefully read the ACI 201 attachment you provided before making my initial post.

1) Submit an alternate ACI 201 mix design as I previously suggested.

2) Along with this alternate mix design accurately list all the steps needed (testing, approval, etc.) and estimated time for each step. Point out in detail how this delay will affect the entire project. Offer to meet with Client to discuss all aspects of this proposal and other options (like waiting months for cool weather to return).

3) Be sure to point out that the mix (microsilica & fly ash) originally submitted meets ACI 201 requirements and is ready for use.

4) Be patient with the Client and let them make the decision on what to do next.

I worked for and retired from a "sophisticated" Owner, responsible for all civil, structural, geotechnical of substantial projects (electric generating stations... $1 Billion+ each), with plenty of 3.5m thick concrete foundations. I've walked the walk, so I'll talk the talk (how to deal with a "reasonable" Owner).

Your goal is to convince your client that they (the Client) have much to loose by not allowing you to proceed.

Take the above steps, or just keep looking for a "technical" answer that does not exist.

RE: Mass concrete

Can you do something like intrusion prepact where you place 'rocks' and have the concrete fill in around? Diminish the high amount of cement paste.
Why such a high cement content for mass concrete?

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

-Dik

RE: Mass concrete

Ever considered cooling piping to control the temperatures?

RE: Mass concrete

Sorry for slightly hijacking but I'm interested in what dik suggested.
dik do you have a liturature or examples where using larger rocks to reduce concrete volume? I have googled intrusion prepact but I can't find a discussion of it.

Kind regards

RE: Mass concrete

It's often used for nuclear containment and concrete dam structures, where some really thick walls are used and some really big aggregate is used... like 16" to 24" 'gravel'. I'll see if I can dig up some info... I used to have literature... but dating back 30 years. I'll see if I can find it (I likely still have it, just don't know where). Spelled it wrong... intrusion prepacked.

https://www.concreteconstruction.net/how-to/intrus...

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

-Dik

RE: Mass concrete

You may want to consider introducing cold joints to reduce the concrete thickness. Does the mat REALLY need to be a continuous pour?

RE: Mass concrete

dik - you mean cyclopean concrete??

RE: Mass concrete

Quote (dik - you mean cyclopean concrete??)


Never heard the term...sorry.

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

-Dik

RE: Mass concrete

'Cyclopean concrete' was the first term I was told, then 'plum concrete'. 'Intrusion prepacked' is the newest for me.

RE: Mass concrete

I first heard about intrusion prepacked about 40 years ago... not a new term...

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

-Dik

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