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Old 08-23-2019, 08:35 PM   #1
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Default Poured a generator pad on a coastal property

This one is just over 12' long, 5' wide and 37" tall. It's for a 150kw 3 phase 120/ 208 gas unit. Electrical with slab 42k 300 amp breaker and a spare 200amp for future fire pump

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Old 08-23-2019, 09:07 PM   #2
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How many days will the slab have to cure before the generator can be set?
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Old 08-23-2019, 10:13 PM   #3
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I would have made a 24" wide foundation and the middle would have been tamped #4 select gravel up to Six " depth below the top of the form, so that there would be 6" of reinforced concrete in the middle and outside full depth concrete all the way around. That thing you made is gonna sink to the middle of the planet.
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Old 08-23-2019, 10:19 PM   #4
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Looks like Santa dyes his hair and flies down to Florida to pour generator pads in the offseason....


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Old 08-23-2019, 10:42 PM   #5
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How many days will the slab have to cure before the generator can be set?
We used 3000 mix with a 5" slump. The concrete companies QC said we could expect to load at 75% in 3 days. The generator weighs in a 3,500 lbs.
We usually strip the next day and set the generator. The owner rep, an crazy property manager type, has become a concrete expert via the internet and was expecting us to cover the slab with burlap and spray it with water every few hours around the clock for 7 days to keep it from cracking.
She also read where concrete takes 20 days to cure and we couldn't put the generator on it until then.
She is causing her property to unnecessarily pay about $100 per day for standby generator rental.
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Old 08-23-2019, 10:47 PM   #6
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I would have made a 24" wide foundation and the middle would have been tamped #4 select gravel up to Six " depth below the top of the form, so that there would be 6" of reinforced concrete in the middle and outside full depth concrete all the way around. That thing you made is gonna sink to the middle of the planet.
It's 7 tons of concrete spread out over 100 square feet. Is that 140lbs per square foot?

I wouldn't think dry rocks weigh that much less than wet rocks. Now If we could have put styrofoam in the middle, that would be nice.
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Old 08-23-2019, 10:49 PM   #7
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Looks like Santa dyes his hair and flies down to Florida to pour generator pads in the offseason....


That's my Bro Jimmy. We have been working together on and off since about 96
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Old 08-23-2019, 10:55 PM   #8
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Did you have tie wire side to side in the forms?
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Old 08-24-2019, 05:21 AM   #9
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Did you have tie wire side to side in the forms?
No and, yes that happened.
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Old 08-24-2019, 07:00 AM   #10
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What is the slab sitting on? Is it a rock or stone base of some sort or did you do footings? I'm curious about the soil conditions it's sitting on.
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Old 08-24-2019, 07:04 AM   #11
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Concrete is about 145 lbs/ft^3 and you're 3' high = about 450 lbs/ ft^2 loading on the soil.

Soil bearing capacity is conservatively estimated at 2,000 lbs/ ft^2.

It's not going to sink to the center of the earth! As long as you removed all the organics and did a reasonable job compacting you're in fine shape.

As to cure time, IIRC you get about 75% design strength in 3 days. Typical concrete cylinders for testing are 3, 7 & 28 days for highrise post-tension where you need to verify strength of the concrete before removing shoring (to prevent collapse).

Keeping it wet does result in a better job. It's a generator pad, not a church aisle or altar.

That's one beefy pad for sure. First thought I had was why not use stemwalls and precast planks, but at around 7 yards of mud, if you can get it all done in one pour, you're in good shape. It would cost more to mobilize to excavate a footing, get an inspection, pour the footing, let it cure, get the masons in, etc... Buy 7 yards of mud and you're out of there.

Where you were nailing that spreader and using the come along, was the form getting away from you there?
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Old 08-24-2019, 07:31 AM   #12
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Quote:
Originally Posted by Southeast Power View Post
We used 3000 mix with a 5" slump. The concrete companies QC said we could expect to load at 75% in 3 days. The generator weighs in a 3,500 lbs.
We usually strip the next day and set the generator. The owner rep, an crazy property manager type, has become a concrete expert via the internet and was expecting us to cover the slab with burlap and spray it with water every few hours around the clock for 7 days to keep it from cracking.
She also read where concrete takes 20 days to cure and we couldn't put the generator on it until then.
She is causing her property to unnecessarily pay about $100 per day for standby generator rental.
Around here a 4000 mix would have cost you around $100 more on a 7 yd load and would have better early strength.

The burlap cure, that is old school finishing at its finest. However no one does that anymore because of labor costs. Most use a curing sealer like Diamond Clear or Cure and Seal that is sprayed on and does a good job.

Concrete takes more than 20 days to fully cure, try 20 years to reach 100% cure strength.
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Old 08-24-2019, 07:46 AM   #13
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in Western PA., a footer would be required because that much weight would sink.
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Old 08-24-2019, 07:50 AM   #14
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hi All
Yes that is for sure a huge plinth for a generator I hope the reasoning behind the thickness is to put the generator higher because I install a 40-60 MVA transformer on a concrete base of about 400mm (160") thick and they weigh 40 ton ???

yes 460 delta they could use technology to seal the slab (no need to put water on for days)
as rule of thumb (small differences in curing time of different MPA and slurry)
3-7 days 50%
14 days 75%
28 days 90%
100 years 100% hahaha
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Old 08-24-2019, 07:59 AM   #15
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On lunch break do you guys set up a little cardboard box theater and put on a sock puppet show?
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Old 08-24-2019, 08:02 AM   #16
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Looks like everyone's confusing maximum ever strength of the concrete with design strength of the concrete. Concrete is typically deigned using a "28 day design strength" meaning that's what's expected in 28 days. I've labored quite extensively in labs cracking those cylinder and often it happens in 3-7 days.

He only needs a fraction of design strength to set the genset.
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Old 08-24-2019, 08:25 AM   #17
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It's not all concrete. Jeffrey Epstein's photographer is at the bottom.
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Old 08-24-2019, 08:27 AM   #18
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Quote:
Originally Posted by MikeFL View Post
Looks like everyone's confusing maximum ever strength of the concrete with design strength of the concrete. Concrete is typically deigned using a "28 day design strength" meaning that's what's expected in 28 days. I've labored quite extensively in labs cracking those cylinder and often it happens in 3-7 days.

He only needs a fraction of design strength to set the genset.
I'm not confused about the ultimate strength, I'm just saying that a 4000 mix is a lot easier to put a finish on and make look nice. I know it's just a genset pad, but I try to put on the best finish I can possibly pull off with what limited skills I have. Around here a 3000 is a footer mix, wet it and jet it in the footing and a hit with a mag float.
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Old 08-24-2019, 08:39 AM   #19
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Quote:
Originally Posted by MikeFL View Post
Looks like everyone's confusing maximum ever strength of the concrete with design strength of the concrete. Concrete is typically deigned using a "28 day design strength" meaning that's what's expected in 28 days. I've labored quite extensively in labs cracking those cylinder and often it happens in 3-7 days.

He only needs a fraction of design strength to set the genset.
Yes Mike i agree
if i buy 25Mpa concrete it will be >25Mpa on the 28th day after poring, this is the specs the supplier guaranty's (the supplier has a commitment to guarantee this so they over estimate to make sure it is 25Mpa)

and i have also had concrete that was on design spec after 3 days (especially with the mix they have there not a lot of water in that mix so probably 35Mpa)
and personally i think with that heep of concrete they can install the generator after 3 hours
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Old 08-24-2019, 08:45 AM   #20
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Quote:
Originally Posted by 460 Delta View Post
I'm not confused about the ultimate strength, I'm just saying that a 4000 mix is a lot easier to put a finish on and make look nice. I know it's just a genset pad, but I try to put on the best finish I can possibly pull off with what limited skills I have. Around here a 3000 is a footer mix, wet it and jet it in the footing and a hit with a mag float.
Up in MD we used a 2500 psi mix for footings.

Mag float on a footing? You must charge extra for that! I'd drag a flat head shovel across it backwards and people would ask me how I got it to look so nice!
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