Drilling the holes for post-installed anchors 2

[WARose]

I've got a project where I am going to put in some post-installed (Hilti) anchors in reinforced concrete. Usually I am worried about them hitting (and damaging/cutting) the re-bar putting them in......but in this case, they've got to go where they've got to go. (And I've checked the footing with these bars cut and it's ok.)

Based on previous experience (and reading through some older threads) it appears going through the re-bar is certainly possible. (Apparently you have to change drill bits.) But what is worrying me based on what I am reading is the time/schedule factor. So my question is: Does it take a great deal of time to get this done? If you need a anchor number and embedment depth: we are talking about a dozen anchors embedded about 24 inches. Thanks.

 

[SlideRuleEra]

Does it take a great deal of time to get this done?

Yes, and it is not practical to rush the process.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[WARose]

Thanks SlideRule. Any idea how much time we are talking? I know it's going to vary for contractor to contractor.....but whatever you've seen, I'd like to hear.

 

[dik]

You can use a diamond core drill and cut the rebar, if OK, and then use a 'wobbler' (Hilti has one, and I don't recall the name of it) that attaches to the drill and 'roughens' the surface. I try to avoid using cored holes and prefer regular impact drills.

Dik

 

[WARose]

Thanks dik. If you've seen this done in the field, any idea what kind of time frame we are talking here?

 

[ameyerrenke]

Getting through 1 rebar can take somewhere between 1 - 6 hrs depending on tools used to get through it, experience and luck! Wet Diamond Coring through rebar is typically the fastest way to get through it, it also has the highest initial cost and creates a smooth surface that epoxy does not adhere as well to. Our crews would typically hammer drill down to the rebar, then either wet diamond core, or use one of the linked bits, then switch back to hammer drilling once they're past the rebar.

Rebar cutter- these typically work best at around 5-600 rpm, with a ROTARY ONLY drill (NON-hammering). These bits often only last 2-3 rebar:

http://www.mytoolstore.com/Relton-RB14-7-8-Rotary-Only-Rebar-Eater-Straight-Shank

 

[SlideRuleEra]

WARose - We had to add vertical rebar to, and in some cases enlarge oversized cast-in-place concrete columns. Numerous drilled anchors were needed in the side of the columns to enlarge them. The long, large diameter holes for the vertical rebar had to be positioned exactly as designed. This was a number of years ago, but I believe it took several days to drill each column. The contact for this work was time-and-material - not fixed price. This was to ensure that the Contractor did not rush or try to take short cuts. Also, we had full time, qualified third-party monitoring of the Contractor's work.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[WARose]

Thanks for the info ameyerrenke & SlideRule.

 

[bootlegend]

I dealt with this situation fairly recently and from memory I believe you can only use the core drill and roughen method for HIT-RE 500 adhesive epoxy. We typically use HY200 but had to use the HIT-RE 500 which has some different working and cure times and I think the hole cleaning methods were a little more detailed. Also had to roughen the hole as mentioned above.

 

[dik]

ameyerrenke pretty much sums it up... may have been lucky on our projects. It typically takes 2 to 3 hours per anchor installation.

Dik

 

[Ron]

I agree with dik's representation of 2-3 hour for such an anchor.

Core drills are limited in size, meaning they are usually not small enough to meet manufacturer's recommendations for hole diameter relative to threaded rod diameter, unless you have really large diameter anchors. This leaves you with the option of hammer drilling the concrete and drilling through the rebar with a steel bit. There are carbide bits that supposedly do both, but they are incredibly slow. I have also tried some that would not penetrate the rebar.

If you use coring bits, run a sandblasting wand down the hole to roughen or use a heavy wire brush attached to a drill to roughen.

 

[Ingenuity]

Core drilling small diameter holes (less than 1" diameter) can be a pain! Moreso if they are deep holes. The small concrete 'core' tends to fracture inside the bit and prohibits water flow to the diamond-tips, overheating the bit (often jamming the bit), sometimes even making the silver-solder bond of the teeth 'melt' and therefore lost diamond segments. Can be very unproductive. Cutting a rebar is also more challenging if you cut the side of the rebar rather than cut through it fulls section.

To give you an idea on production: We did a repair project in 1999 to a power plant foundation that had 220 core holes x 1-1/2" diameter x 72" deep - we used acid to 'etch' the core hole walls for epoxy bond, then copious amount of water to neutralize the acid solution (then check the pH of the concrete). Production was 220 holes in 21 days (including epoxy work) so about 10 holes per day. 2 core rigs were used, with extendable bits to reach the 6' depth.

I would expect 12 holes x 24" depth x small diameter (depending on access etc) to take 2 days with a 2 man crew, so about 32 (wo)manhours.

 

[racookpe1978]

Smaller dia concrete hammer drills are modestly flexible, as are the corresponding smaller dia anchor rods. (those less than 1 inch dia; 1-1/2 to 2 inch are obviously rigid, but core drills work easily at those dia's as well). The smaller the drill or anchor bolt dia, the less likely it is to hit the rebar directly in the center - So many times, your drill bit will deflect sideways when it strikes the side of a hidden rebar rod, with no realistic loss of top position, verticality of the exposed anchor bolt up above the surface, and net strength. In fact, you may strike many rebar and never know it.

 

[DETstru]

Cleaning and prepping the holes for epoxy with core drilled holes is a real pain. I've had a lot of trouble making sure contractors follow through with the correct procedures.

Hilti claims this adhesive product is better for core drilled holes:

https://www.hilti.com/content/hilti...-firestop-strut/concrete-anchors/re500v3.html

There's more info in the "For Installers" button a ways down the page.