Popouts as you described are caused by expansion of aggregate. Some of your aggregate probably contains chert or some other expandible material. Alkali silica reaction is also suspect. You would need petrographic analysis to be sure of the cause.

https://cti-ia.net/what-are-aggregate-popouts-how-...

In this locale, chert is a common cause.

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

-Dik

That is interesting. So the pop outs I'm facing typically are visible within the next couple days after placement and only 1/8" thick of peeling is occurring

Thanks hokie / dik. Not something I have come across previously. Very neat.

Not to hijjack the thread, but dik you say it's common in the western provinces? Does CSA A23 not limit the amount of said aggregate in the mix or is it left up to the supplier as long as they meet the other prescriptive requirements? If allowed by A23 how should one specify the mix such that issues dont arise with architectural concrete?

@hokie66
Do you have any previous experience with manufactured sands in a mix design?

Common to the provinces may be a stretch... common to locales, maybe. There may be a source of aggregate 100 miles away with no alkali reactive aggregate.

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

-Dik

@dik
I did a small amount of reading on chert. If it were chert there would be a larger piece of pop out? Am I understanding correctly? When chert occurs the surface along with the aggregate end up popping out, at least that is what I gathered.

Agree with hokie66's assessment. Alkali-silica reactivity or alkali-carbonate reactivity usually cause this. Lift up one of the delaminations and it will be a slightly conical shape with a soft white or yellowish/greenish powdery or gooey substance at the apex. Powdery if now very dry, gooey if the concrete is exposed to moisture.

The usual culprit is small pieces of chalcedony chert in the coarse aggregate. As hoki66 notes, a petrographic examination is necessary.

In its most subtle form, it is a surface aesthetic nuisance. In its most aggressive form it can be destructive to the entire cross-section of the concrete.

I replied to the thread without reloading the current page. One question....is there a piece of aggregate at the center of the anomaly? You mentioned "peeling". If there is no coarse aggregate at the center of the popout, then you might have blistering, a finish issue. Blistering is usually caused by trapped bleed water and overtroweling, but it is also usually not consistently small and round. The shapes can be random and they can be fairly large.

Can you post photos?

No reference for size, but those look larger than a silver dollar. As per Ron's last post, I now think your problem is finishing gone awry. Back to school for those finishers.

Definitely not alkali aggregate reaction... much more like blistering...

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

-Dik

Yep...blistering and scaling. This is caused by poor finishing techniques. Bleed water got trapped under the surface. Hard troweled too quickly.

I don't think I've seen better photographic examples...

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

-Dik

150% that is a finish problem. Either on too early as Ron suggested or too much water at the time of finish or if it is air entrained they densified the surface too much with the trowel. What is the mix? Are you using a super-p admixture? If not, the finishers have a tendency to throw water on the surface like they are blessing it.

I'd chain drag the entire surface. While those may be the apparent scaling areas at present, my money is on the problem being much more systemic. The consequences of which might only be seen in service.

@dik....I agree. Those are excellent examples of the issue.
@structuralconcrete.....would you be willing to share the originals of those photos? I am starting editing of the next edition of my textbook and there might be a place for those in the book. You would be credited in the caption.

I've done the chain drag test and it is isolated to just those areas. What confuses me is that its so isolated. These pictures are as bad as it gets the majority of these areas are reduced down to silver dollar size though.
If it is indeed a finish issue, why is it just isolated to like 2-3 locations?

@structuralconcrete....that's not unusual. Water distribution varies within a concrete mix as with all the other constituents. If the concrete is not adequately mixed, you get variations in air voids, water gain voids, aggregate distribution and random locations of anomalies develop as a result. This can result from insufficient drum rotations or dirty/impacted or worn mixer blades.

It can also result from the finishers throwing water on the surface during finishing to re-wet the surface or throwing dry cement onto the surface to dry up spots of heavy bleed water.

For these reasons, it is good to do an audit of a ready-mix supplier if you are placing a large area of concrete. The National Ready Mix Concrete Association has a good checklist for doing a plant audit. I've done many over the years. One particular outcome of a plant audit is that they will know you are serious about concrete quality so they tend to pay more attention to your deliveries. Further, the concrete mix must be properly paired with the application and the placement methods to be used. For instance, for slabs on grade, use the largest coarse aggregate that can reasonably be placed for the application. This will keep the cement content lower, the water content lower and will reduce shrinkage.

Concrete is not as simple as the concrete subs would like to think. Remember....good concrete is made with quality aggregates, good portland cement and clean water. Bad concrete is made with the same ingredients.

@Ron
Your feedback has been very insightful. One comment I do have is that during the finish process the finishers have not done any of the above. They did not use any water to wet up dry spots or use powder to dry up wet spots. I find it hard to believe that it was indeed a finish issue although I do not rule it out.
So I've mentioned several times that I am fairly new to concrete, I have learned a lot over the last 6 months. One thing I notice during the placement of the slabs where this "peeling" has occurred is that the mix loses 1.5-2" of slump from the truck to the end of the hose. Could this be the cause of dirty materials used for the mix?

Also, what are the subjects you are covering in your book?

@structuralconcrete.....my book is a textbook that is used by about 50 colleges and universities in the US and Canada for Construction Engineering and Construction Management Programs. It is a general coverage of a variety of topics. The title is "Principles and Practices of Commercial Construction" and is published by Pearson.

Well, ain't that funny. I certainly have Ron's book on my shelf. I use it mainly as a general pointer on how to think about subjects I don't do day in and out. I typically cross reference it against Fundamentals of Building Construction: Materials and Methods which was written by a pair of architects (something which I struggle with because....it's by architects!!)

Also, appreciate the shout-out in your preface haha

Great book... I tried to get a couple of lecturers use it for their courses without success...

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

-Dik

Thanks, Guys. I appreciate it. I try in each edition to improve the information. If you have suggestions, I would appreciate them!

Quote (If you have suggestions, I would appreciate them!)

I didn't think the first one could be improved on.

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

-Dik

Thanks, Dik....very kind.

Ron,

Could you post a complete citation for your textbook?

Jim

Gud buk

Dik

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

-Dik

@dik...

@Jim...I try to not promote my book on the site, but have been asked for the title a few times.....thanks for asking.



"Principles and Practices of Commercial Construction", 10th edition, Pearson
W. Ronald Woods, Cameron K. Andres and Ronald C. Smith
ISBN-13: 978-0134704661
ISBN-10: 0134704665

Both Cam Andres and Ron Smith have long since passed away.

@enable...where are you in Ontario? I used to be a partner in an engineering firm based in Toronto (Brampton). At that time it was The Trow Group....now it is exp

Ron, we are in Oakville but I know Trow moderately well. I'm not sure of your timeline but you may even know my father as he was part of Trow several decades back. I'm not certain of his title but in effect he ran the restoration division in the early to mid 1980s before branching on his own (maybe David Cousins rings a bell). I always found his choice of office location particularly humorous because he bought a unit not 5 minutes down the street from the Trow main Brampton location.

Small world!

@enable....a small world indeed. Yes, I recall the name. I worked closely with John Bickley, the concrete guru; Chris Thompson, the head Geotech, Vlad Stritesky, the roofing guru, and John Emery, the pavement guru (John left Trow and started JEGEL...specializing in pavements and geotechnical. I ran the US operation at that time (1983-1989), before buying out my partnership and then selling to a larger, international firm....Law Engineering, a company that I worked for before starting my own business and then associating with Trow.

Trow was a class act. Bill Trow's legacy lives on. Will forever remember my association with great fondness for the friendships and professional interaction.

Thanks for the history, Ron. John Bickley was the first real concrete expert I met... he was well versed in concrete parking garage deterioration due to salt... one of the first.

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

-Dik