Setting Turbo Separator after 1 day Cure Time of High Early Strength Concrete

[structengr23]

I have a dilemma where the client wants to set a dynamic piece of equipment on a 2' thick concrete pad that is doweled onto an 8" thick elevated floor (second floor) only 1 day after setting the concrete. He is proposing high early strength concrete that is shown to achieve 3900 psi after 24 hours of curing, but everything I research (including ACI C150) says wait a minimum 3 days cure time for Type III Cement. The client claims that they've done this for previous 400 HP Compressors and had no problem. I am looking for code justification for setting a dynamic machine after only 1 day cure time for HEC. They also want to start it up and begin running the machine after only 7 days. All of this is to achieve a short window of time in the plant turnaround.

 

[CELinOttawa]

My comment is based on this 2" thick pad and equipment placed onto the one day old 8" thick floor.

I will be interested to see other replies, but this makes me very, very nervous. Just like durability correlates well with compressive strength but is a different parameter, strength does not dictate the creep and deflection characteristics perfectly, and my instinct is this is going to cause problems. My best bet is creep, but I would not rule out all kinds of issues.

Not sure I can contribute meaningfully, but I thought I would chime in even if only to echo your concerns.

If you meant that the 2" pad is one day old, I don't see an issue at all. Dry pack can and is frequently done in such situations, and is far stronger than needed. I wouldn't have an issue with many pieces of equipment going into service the next day in such a scenario.

 

[jayrod12]

There's concrete mixes used for bridges and roads that are able to be driven on the next day, so there's got to be some leeway on that. And in terms of just setting up the machine, I don't necessarily see the issue. If they aren't turning it on for 7 days, then what would be the potential issues with setting it early?

 

[SwinnyGG]

This type of thing is done all the time.

The load from setting the equipment on the pad is typically (I don't know specifics of this equipment, but in general terms) only a fraction of the actual load in service due to vibration.

Setting the equipment on day 1, for a pad poured with high early, wouldn't concern me much. If they wanted to start and run the equipment on day 1, might be a different story. But if you're getting design strength at 7 days, I wouldn't expect a problem. Especially if this equipment is indoors where winter weather isn't going to affect the maturity of the pad after it's placed.

I would be more concerned about a 2' pad plus equipment going onto an 8" elevated deck.. but I imagine you've already calc'd out that part of this scenario.

 

[canwesteng]

My only concern is making sure the concrete still cures. You'll have to use a curing compound before setting equipment. Otherwise no issue, this is done often as swinny says.

 

[AskTooMuch]

Your client maybe referring to this

https://www.rlrowan.com/images/pdfs/r-crete plus installation bulletin bucket mix.pdf

 

[SwinnyGG]

I've never heard of that product.. every competent concrete plant in the world will have high early mixes on file which are standard concrete with an accelerator, available in whatever ultimate strength you want pretty much.

 

[structengr23]

Thanks for the feedback. The 8” floor and 2’ mat span across 3 hefty steel beams. I definitely checked that first.

Good feedback on the HES concrete. The mix design proposed is a Highway mix, so it has quick usage history. One point mentioned is the bond between the machine grout and the mat. With water sweating from and bleeding from curing, the bond of grout to concrete can be compromised if set too soon.