Miami Beach, Champlain Towers South apartment building collapse, Part 15 32

[SFCharlie]

A continuation of our discussion of this failure. Best to read the other threads first to avoid rehashing things already discussed.
Miami Beach, Champlain Towers South apartment building collapse
Miami Beach, Champlain Towers South apartment building collapse, Part 02
Miami Beach, Champlain Towers South apartment building collapse, Part 03
Miami Beach, Champlain Towers South apartment building collapse, Part 04
Miami Beach, Champlain Towers South apartment building collapse, Part 05
Miami Beach, Champlain Towers South apartment building collapse, Part 06
Miami Beach, Champlain Towers South apartment building collapse, Part 07
Miami Beach, Champlain Towers South apartment building collapse, Part 08
Miami Beach, Champlain Towers South apartment building collapse, Part 09
Miami Beach, Champlain Towers South apartment building collapse, Part 10
Miami Beach, Champlain Towers South apartment building collapse, Part 11
Miami Beach, Champlain Towers South apartment building collapse, Part 12
Miami Beach, Champlain Towers South apartment building collapse, Part 13
Miami Beach, Champlain Towers South apartment building collapse, Part 14

SF Charlie
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[MarkBoB2]

If the deck collapse started at the wall on the southern end of the deck and then progressed northward toward the building, then why don’t we see the collapsed deck in the TikTok photos posted by Sym P. le above? These photos appear to show sprinkler pipes and drainage pipes that were hanging from the garage ceiling underneath the deck, but no trace of the deck itself. Could the deck have not fallen yet in these photos?

 

[spsalso]

"When Champlain Towers South was built chloride ion content in concrete was uncontrolled."

Really?

Then it was accepted to use salt water in concrete mixing in 1980? THAT would be pretty uncontrolled. And provide LOTS of chloride.


spsalso

 

[MaudSTL]

…why don’t we see the collapsed deck in the TikTok photos…

Here’s the perspective of the TT video. There wasn’t enough light to see beyond the rubble to the collapsed deck outside of the building. From the Miami Herald House of Cards infographic:

 

[IanCA]

Feb 22 04:49
"When Champlain Towers South was built chloride ion content in concrete was uncontrolled."

Really?

Okay, I admit I was winging it a bit in that post due to time constraints. Perhaps "unregulated" would be a better phrase. But I have since found more good supporting evidence:
Evaluation-of-Chloride-Limits.pdf

"Chloride ions present in deicing chemicals and seawater are the primary source of external chlorides that can migrate to the reinforcing steel in concrete to cause corrosion of steel in concrete." I believe we need to add a third source.

"The current ACI 318 Building Code chloride limits are based on research in the 1980s with primarily portland cement mixtures."

Literature Review of Chloride Threshold Values for Grouted Post-Tensioned Tendons
This document, on page 6, shows research was being done on chloride concentration in concrete as early as 1975

"The first comprehensive literature review of chloride threshold values was done during efforts to investigate the most accurate way of representing chloride threshold values.(18) Among 20 chloride threshold values reported by Glass and Buenfeld
Glass, G.K. and Buenfeld, N.R. (1997). They concluded that total chloride content relative to weight of cement is best for expressing a chloride threshold value"

"The investigators were able to confirm that tendon failure by strand corrosion can be realized in as little as 7 years"

"If the strands were embedded completely in grout, both unstressed and stressed strands experienced similar capacity reductions. If they were exposed in the voids, the stressed strands experienced much higher capacity losses (more corrosion damage) than the unstressed counterparts. The largest mean capacity reduction was observed when the stressed strands intersected the voids perpendicularly in grout that was exposed to 0.006 and 1.8 percent chloride ions. The researchers concluded that it is important to protect the ducts and strands from water and chlorides and also to eliminate grout voids to prevent or minimize the strand capacity reduction. According to their reliability model, a PT bridge can fail as early as 21 years after construction if the strands are subjected to high-chloride environments. "

Also of interest:
Determination of Chloride Content in Cementitious Materials:

 

[IanCA]

11 Feb 22 00:54
If the deck collapse started at the wall on the southern end of the deck and then progressed northward toward the building, then why don’t we see the collapsed deck in the TikTok photos posted by Sym P. le above?

@MarkBob2, I think it is possible that the north side of the deck was still supported, attached, or partially attached to the columns and drop slab that ran east-west along the south side of the portion of the building that collapsed (at row 9.1/10). Or even that some columns along 11.1 had not yet punched through. I can imagine parts of the weaker planters breaking away and dropping through the deck while stronger areas, where beams were present, remained intact for a few minutes.

 

[AutisticBez]

Regardless, I'm sure it got into the 40 year old structure of the pool deck, one way or another.

 

[dik]

Chlorides and corrosion have been know to be a problem since the early 70s.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[spsalso]

This article:

Link

says:

"Chloride ions can penetrate into the concrete and cause accelerated corrosion of the reinforcement. The chemical reaction of the cement paste with the high-chloride content of seawater is generally slight and not a primary cause of concern."

This would seem to mean that if chlorides got into the pool deck, it would show up as corrosion of the rebar, and not affect the concrete.

So, while the concrete of the pool deck would not be affected, there should be some nasty looking rebar showing.

Where is it?


spsalso

 

[dik]

This makes me question the latest concrete repair. IMHO, both the concrete strength and the concrete cover was way too low.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[zebraso]

The chemical reaction of the cement paste with the high-chloride content of seawater is generally slight

That statement might rely very heavily on the context of time. Or it just might be wrong. Sodium is very reactive with many elements. ferrous metals are not the only thing that are subject to corrosion from what I understand. Acidic reactions will break down the cured concrete paste most assuredly. And I believe (not totally sure) that sodium chloride creates a mildly acidic pH in the concrete pores. I mean how do we expect the chloride to get to the steel if the concrete is impervious aside from the odd crack that forms? That can't be the mechanism that is most worrisome or the only one. Where are the chemical engineers on this website?

 

[dik]

Chlorides reduce the passivity of the high pH of concrete and greatly enhances corrosion of the rebar. Check the link:

https://www.engineeringenotes.com/c...ability-of-concrete-concrete-technology/32209

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

It's the high pH that provides the passivity to prevent reinforcing degradation... the chlorides reduce this protection.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Someone might want to start Part 16...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[zebraso]

sulphates in concrete create acidic compounds also with moisture. aluminum content forms crystals that expand and cause cracks etc. I have to agree with your statement that the original quality and cover of the concrete means a lot. And we have not heard whether they used beach sand or not.

 

[dik]

and that's why they have Type 5 or Type 50 or Type HS (in Canada) concrete... two different critters, here and quite unrelated. Our clays in the Winnipeg area are high sulphate, but this can be overcome. They will still suffer from corrosion issues in chloride environments. The fact that the engineer did not address concrete strength and cover leads me to be a little curious about his qualifications.

catch the link:

https://www.understanding-cement.com/sulfate.html

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[zebraso]

Well I think we heard the cores were "curious". Amazing.

 

[dik]

"curious" and a couple of bucks will get you a cup of coffee, in these environs.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[zebraso]

Yeah, I thought curious is where you start, not finish. So nobody gets cream and sugar with their coffee.

 

[spsalso]

And yet no one has pointed out examples of badly corroded rebar, yet.

I'm not saying it didn't happen. But show me!



spsalso

 

[IanCA]

And yet no one has pointed out examples of badly corroded rebar, yet.

I'm not saying it didn't happen. But show me!

Also, at 24 seconds in the Fiorella Terenzi CTS garage walk-through video, that looks like iron oxide in the runoff on the ceiling to me.

Garage walkthrough video