Too cold for shotcrete?

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I was told at 28days it will come out to 5500-6000psi?

I have called about 5 civil engineering firms in Phx this morning and one concrete contractor, they think I am from Mars when I ask these questions and none of them do consulting eval.

Am I really asking scary questions? It’s crazy I can get a 2nd opinion for surgery and nobody thinks twice about it. Try to ensure my concrete pool is sound, lol, are you crazy???

any recommendations for a 2nd opinion let me know. PB is acting like I am the most difficult client on the planet, nobody has every asked these questions. I guess I am crazy, lol.

I did get the name of the civil engineering firm that did my design specs, they tried to push me back to the PB until I told them the PB pushed me to them. They said send over pictures, iI am going to ask for the design specs, and the batch tags from the concrete.

I am politely asking these questions and I have not threatened or anyone or been rude in anyway. They just start freaking out when I ask questions that nobody else does and they don’t have answers.

Starting to wonder if I am Pi$$ing into the wind here, lol.
 
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Titan7 said:
Am I really asking scary questions? It’s crazy I can get a 2nd opinion for surgery and nobody thinks twice about it. Try to ensure my concrete pool is sound, lol, are you crazy???

any recommendations for a 2nd opinion let me know. PB is acting like I am the most difficult client on the planet, nobody has every asked these questions. I guess I am crazy, lol.

I did get the name of the civil engineering firm that did my design specs, they tried to push me back to the PB until I told them the PB pushed me to them. They said send over pictures, iI am going to ask for the design specs, and the batch tags from the concrete.

I am politely asking these questions and I have not threatened or anyone or been rude in anyway. They just start freaking out when I ask questions that nobody else does and they don’t have answers.

Starting to wonder if I am Pi$$ing into the wind here, lol.
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You're not crazy at all.

The problem is the pool building industry is not very professional in many ways. And, especially here in Arizona, the trades are full hacks and fly-by-night operations and people who are interested in making bank and ignoring quality (because quality takes time and effort to achieve). Pools are a luxury item and so most engineering firms see them as a way to make a quick buck with little interaction. There is almost zero liability for anyone involved in the process if something catastrophic goes wrong and they see this simply as a matter of you taking what you get and, if there's a problem, your insurance company will cover it. This isn't some public works project like a roadway or bridge or skyscraper that costs tens of millions of dollars and could involve huge liabilities if a mistake is made ... it's a backyard pool and so it's just "low rent" engineering.

Also, your PB is most likely not an expert in any of this. They are, for the most part, glorified schedulers, paper-pushers and check collectors. It would be surprising to me if they knew anything about the details of structural concrete work and so they simply pass the job off to the subcontractor that also , supposedly, knows what they are doing. That's why when you ask questions you get blank stares and dead silence on the phone, they don't know and they probably don't even know who to ask.

At the end of the day I think your pool will be fine. Assuming the surrounding ground in the area is stable, it's highly unlikely that the shell will have any problems. We live in a very geologically stable area and so as long as you are not doing some kind of construction on a huge slope or in sinking ground, the pool will be fine.
 
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Titan7 said:
I was told at 28days it will come out to 5500-6000psi?
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3,000 psi is a nominal rating and the final can be higher, but I would not believe it until the test actually proves it.

I would get it tested at 28 days.

If the strength is not at least 3,000 psi, I would be concerned about the likelihood of future cracks.
 
MAPR-Austin said:
To someone who is more familiar with the process: is it normal to shoot all the walls out to the rebar like that and then come back to continue buildout?

I feel like the times I have seen it done they bring the wall out to the full thickness on the first pass or very soon after the first pass.
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Typically, you want to shoot the full thickness and not allow the earlier concrete to set.

There is a whole training course on shooting gunite and shotcrete that goes into the proper placement of the concrete.
 
JamesW said:
Typically, you want to shoot the full thickness and not allow the earlier concrete to set.

There is a whole training course on shooting gunite and shotcrete that goes into the proper placement of the concrete.
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Thoughts on how shooting everything out to the rebar and then coming back to build it the rest of the way out like they did would effect the strength of the walls?
 
MAPR-Austin said:
Thoughts on how shooting everything out to the rebar and then coming back to build it the rest of the way out like they did would effect the strength of the walls?
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It depends on how much time elapsed and if the concrete set.

If the concrete had accelerant, then it sets faster.

Hard to tell without knowing the actual shooting progression and how long the concrete sat before the wall was filled out.

Air temperature, humidity etc. also affect the time it takes the concrete to set.

Shooting gunite or shotcrete is a skill that most people underestimate.

It requires a lot of skill, training and experience.

If a company does not have a really good nozzleman, then the quality is going to be inconsistent.
 
You can core drill samples yourself if you want.

You can rent a 4” core drill and bit for a day and maybe get about 4 samples cores and then take them to a local testing lab.

The lab will put the samples in their hydraulic press and compress the samples until they crack and then that will tell you the strength.

Of course, the builder is going to probably wonder why the gunite shell looks like Swiss Cheese.

 

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4" holes should not affect the shell or cause leaks.

A diamond core drill should be able to cut through rebar.

Note: This is just my opinion.

I am not giving you advice and I am not recommending anything.

Do not rely on my opinion for any purpose.

You should make sure that you clear everything with your builder and the engineer before deciding what to do.
 
12.5664 in^2 (square inches) x 3,000 psi = 37,700 pounds of force to crack the sample.

radius | 2 inches
area enclosed | 4 π in^2 (square inches)≈12.5664 in^2 (square inches)
circumference | 4 π inches≈12.5664 inches

The 4" diameter cylinder (at 28 days) should be able to take about 38,000 pounds of force or about 19 tons before it fails.

38,000/12.5664 = 3,024 psi.

20 tons = 40,000 pounds = 3,183 psi.

If the 28 day old sample does not reach about 40,000 pounds, then I would say that it is not meeting its rated strength.

I would say that the absolute minimum force should be 31,416 pounds, which is 2,500 psi.
 
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This whole this just blows, this is my 3rd pool and I have never seen these crazing cracks, i can only see one actual crack on the wall that I cant even get 18g wire into it, I can see it. I have to get a second option on why this happened, it not NORMAL.

not sure I want to drill a bunch of core samples out until I can get an unbiased option from somebody who knows more than me. Just very frustrating.
 
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The cracks look like more than surface cracks.

A few core samples should help determine the strength of the concrete and how deep the cracks go.

You will probably need to drill at a few cracked places as well as at a few uncracked places.

Hopefully, you can find a local expert that can help you navigate this.
 
The holes/dots in the picture are all the same size, but the ones that are farther away look bigger.

Also, since the picture is 2D, the dots are the same distance away.

There are no "closer" or "farther" dots.

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update, well I have called 5 civil engineering firms here in phx and a concrete expert, it seems that nobody in Phx does this type of consulting for residential work, lol. I am still waiting on a call back but I find it really hard to believe I am the only person who has needed this type of service. Last night it got down to 31F, water in my hose froze a little, lol. So I looked at the cracks close today, a business card won’t come close to fitting so I got out my feeler gauge, those are hard to use as the cracks are not strait.

It looks like they are .007-.008”. The engineering firm that did my design saw the picut and said it does not look like cold weather damage but rather poor workmanship from putting shotcrete up in layers, recall the time gaps between trucks, not sure that this issue but they also recommended grinding a few cracks to see if the go deeper.

i got the ready mix tickets, 3000psi 3” slump. i let my PB know what’s going on IMG_4576.jpegIMG_4575.jpegIMG_4573.jpegand have not heard a peep today. All all ears for any suggestion, I post to help me and of course help anybody else out there but I am not sure what else I could have done. What’s also odd is the broom finish on the lower 3/4 of the wall where all the crazing cracks are, the top 1/4 looks like my other pools.
 
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Great that you were able to talk to the engineer who designed your pool. What is their opinion on the cracks? If they are not concerned then I wouldn’t get too worked up over it. You did pay for their expertise after all.

Are they local and willing to see you pool in person? If so, their fee may be worth your peace of mind.
 
.ben said:
Great that you were able to talk to the engineer who designed your pool. What is their opinion on the cracks? If they are not concerned then I wouldn’t get too worked up over it. You did pay for their expertise after all.

Are they local and willing to see you pool in person? If so, their fee may be worth your peace of mind.
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They said poor workmanship and the cracks were most likely cause be delays and stages of application. No they will not come to the house this was based on pictures. They suggesting grinding some of the cracks to see how deep they go. Clearly I not doing that unless the PB is handling. I‘m still having issues getting someone to come out and look at it.
 
You can core drill samples yourself if you want and bring them to somewhere that has a hydraulic press.

It's pretty simple, rent a 3" or 4" core drill for the day and take some samples.

Find a local place that has a tester and have them put the sample in the press.

Compress to failure and divide the force at failure by the cross sectional area to get the psi.

A local University will probably have an engineering department that will do it for you.

You can probably mail the samples somewhere.

The samples should be 28 days old.

I think that you can drill the samples now and they should age the same way as if they were in the shell as long as the conditions are the same.

Note: The builder is probably already annoyed at the oversight and drilling holes is probably only going to make them more annoyed.

So, you have to consider how this is going to affect the relationship with the builder.
 

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