Is it just me or am I crazy.

[itzobi]

Im a senior materials tech for a local D.O.T.

My latest assignment has brought me to a bridge deck that has some serious cracking issues in the entire slab, there are no prestress members or post tension cables present fyi.

The materials P.E. over our department instructed me to use my coring drill to take cores 12" deep, and to "just cut through the rebar". Then just patch the holes back with ordinary post hole mix at a low w/c ratio. The consultant firm hired to oversee the coring only showed up on the first day, and no one bother to mark my core locations. I am using some rudimentary measurements on a single sheet from the as-builts, that I have no idea who signed off on. To top it off, the P.E. told me to just break the cylinders in the compression machine, even if they have rebar in them, to which I immediately told him the ASTM C42 explicitly states to not break them if reinforcement is present, he did really even care.

I cant help but disagree with every decision made, am I crazy?

My personal opinion is this, determine safe locations for rebar (structural p.e.), mark them (consultants job), patch them with fast set concrete or high strength grout(my job), and trim them in accordance with the ASTM and avoid all reinforcement in my test cylinders to determine a true strength. But what do I know, I only have a G.E.D.

 

[apsix]

From the information that you have given, I agree with your opinion.

If that is not possible, proceed only by following written instructions.

Re breaking cores with rebar, just note the presence of rebar in the comments section, adding that the results are therefore not valid.

 

[itzobi]

Honestly I dont even see why he cares about the rebar being in it, the slab had 2" of cover for the top bars, my core is 10-12" long, I can easily trim it and obtain the proper length to diameter ratio needed for a proper test. In my spare time, I plan on breaking one with rebar and one without, to see if there really is a difference in load. The bars are #4 and #8's btw. I destroyed one drill bit already by following his instructions, and I have come up with my own improvised method of determining the locations. I first utilize a Zircon MT-6 metal detector, then, if I core and hit rebar still, I back off and rescan, and drill again. The spots that I back off from, I remove the partial, and fill it like the rest with post hole mix. So far, I am succeeding with this approach and all cores now are rebar free. I agree with getting it in writing, but he is my ultimate supervisor for the department, I dont want to rock the boat. I know he is wrong, I am just looking for some validation to my opinions from some structural p.e.'s

 

[kelowna]

You are not crazy.

I would agree with your approach. There is no reason to core through steel if you can avoid it with a re-bar detector easily, and even if the cores have some re-bar, as you say, you can trim the sample and get it right.

Apsix had good advice, get instructions on writing. Maybe tell him you can get the samples without re-bar on them.

I do not think being right is going to help you though!

 

[itzobi]

Well, the guy has a doctorate degree, so I cannot argue with that, all I have is special inspections certification, but at least I know I am right, even if I have to keep it to myself. I am going to proceed with my method regardless of instructions, and just keep quiet about it. I don't deliver invalid test results, and for the most part I do things by the book, otherwise it is a waste of my time.

 

[itzobi]

I see your point about trying to be right, but if someone constantly goes against ASTM standards with no research to back their claims, how can you use this as actual valid data? One minute he wants to go by such and such ACI code, but then not follow the ASTM procedure. I wish the line of communication was much more open, but its not, so it sets up an adversarial relationship. Test results in our lab are often invalid and not performed by AASHTO or ASTM specifications because of him. I have had it already.

 

[apsix]

As you know cylinders/cores basically break by shearing & splitting.
If rebar crosses a potential break plane the test will be affected.

 

[Ron]

itzobi...your procedure is correct. Your P.E. is wrong, based on your description. Don't test the core with the rebar in it. A compressive strength test is a triaxial test (with no external confining pressure), so anything that interferes with the triaxial stress distribution will cause an erroneous result. If I were reviewing your results I would reject them if tested with the rebar in.

Just because he has a PhD doesn't mean that he knows anything but theory. In this case, he's blowing the theory and the common sense.

Stick to your guns... have him join here and post his reasoning for doing it "his" way. That will be an interesting thread. Good luck.

 

[graybeach]

Unfortunately your PE has not learned to listen to what the techs are saying. I generally find that techs know a lot more about their specific areas than I do so their advice should not be ignored. Usually techs either have a better idea or, if not, they really care and want to understand why their idea is not right.

 

[ToadJones]

Don't ever fool yourself into thinking a P.E. or a PhD means anything more than the paper it is printed on.
Don't get me wrong, it definitely can mean something depending on the individual. However, having the PE or PhD doesn't qualify ones knowledge outright.

Testing the core with the steel in it would be foolish and quite possibly could damage very expensive testing equipment.
If I put a cylinder in our testing equipment that had steel in it or instructed someone else to do so, I'd probably lose my job.

 

[JAE]

A PhD is a warning to me anyway. I have the highest respect for common sense, B.S. and M.S. degrees, good experience, knowledge of codes and standards, etc.

His PhD doesn't give him authority over truth.

 

[Teguci]

PhD's are good for hourly billable projects.

 

[ToadJones]

Teguci-
That got a good chuckle out of me....the funniest part being that I have seen it actually happen.

 

[Qshake]

What kind of bridge superstructure are working on? If you have 12" to core through you must have a solid concrete slab deck, or even a voided slab deck or maybe even a concrete box girder (w/o post-tensioning).

What size core are you using? 2" diameter? For any of the above mentioned bridge decks, you will be hard pressed to find any area free of rebar greater than about 6" x 6" and that depends on the top and bottom mats of rebar being insync. Moreover, depending on the spans you will likely see some large rebar, #8 or larger in the postive or negative moment areas, which I think would tear your core up before you finish.

And be mindful of the last few inches of coring....don't want to lose that core to the river or highway below!!

As to strength concerns, I wouldn't not be too concerned with that for a small diameter core. I would be more concerned about the service conditions following the coring and patching....use the higher strength mix for better durability, adhesion to existing so as to prevent as much water ingress as possible. Ultimately though, the deck will wear much faster here....though if it's cracked and a candidate for possible replacement, it won't really matter anyway.

Good luck.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[itzobi]

We are using the 4", I cant remember which ASTM # it is, but it basically states that anything less than 2" in diameter will result in lower than expected load results. When using a 2" bit, your specimens ends up at about 1.8-1.9", the bit measurement is from the outside dimensions.

Im no bridge engineer, so I cant tell you what exactly its design is, it has a 4 spans, with a series of columns in between, it is about 24" thick.

The rebar in the deck close to the approach slabs gets much more dense, but I still yielded several rebar free samples.

While the compression test would be the tell all method for determining compressive strength, I also dont see the logic in drilling dozens of 12" deep holes in an already damaged and previously repaired bridge, then fill them with post hole mix of all things. When there are so many other non-destructible methods of determining in place strength of concrete.

 

[Ron]

itzobi...The core diameter should be about 3 times the maximum aggregate size...so if you have the typical, No. 57 stone, then the core should be at least 3" in diameter. That will give you a reasonable stress distribution in the core for the compressive strength test. You have plenty of thickness to get L/D = 2.0, so no correction is necessary.

I would save the upper 3 or 4 inches of the core for a petrographic examination. That's the area most affected by placement, environment, and serviceability issues.

As for missing the rebar...there are several methods available to detect the rebar pattern, even if you don't have drawings. As Qshake noted, the rebar will be tight...but if you check upper and lower mats, you should be able to miss most of it...sometimes you just have to cut through..but we don't just cut and not worry about it...we try to miss the rebar. If we can't then we cut in the most innocuous area that we can.

Now...go kick your P.E. in the a$$ and tell him to read this thread!! As graybeach noted, it's ridiculous to not listen to a Senior Tech. Most of them know more than the P.E. about what's important, particularly when it comes to testing. I know...I was a tech before I was a P.E.

 

[itzobi]

You're right, I remember reading that in C42, but didn't really think about it, good thing I did not opt for the 2", it wasn't my choice anyway.

As much as the Zircon MT-6 is touted by Luke Snell, I have had hard time locating the pattern, once I find an offset without rebar I stay with it the rest of length of the bridge.

The engineer would probably raise an eyebrow at me if I told him to do a petro on it. Too bad he wasted the tops and compressed them already, lol.

I would love to kick him in the arse, but these times are tough, I need the job.

 

[hokie66]

You stated that the problem with the bridge was a lot of cracking. Compression testing of cores will probably add little information in investigating why the cracking occurred. Maybe your PhD boss knows that, thus his cavalier attitude toward the coring. On the other hand, as Ron recommended, petrographic examination can contribute greatly to understanding the problems of the deck. So if the PhD doesn't know that, he needs to find another line of work. Sorry for the position you find yourself in.