Notes for core drilling existing concrete 1

[Schneidly]

I have a project where requiring the core drilling of several walls. The cores will 34IN in diameter. I also have a hole that will have a diameter of 54IN. That is a big hole to core. I believe the contractor will need to special order a drill or drill several smaller holes in a circle and go from there. I am looking for typical notes for the drawings. Also, what sort of notes should be included for the treatment of the cut reinforcing?

 

[asixth]

1. REBATE THE CONCRETE AROUND THE REINFORCING BAR(S) AND CUT BACK REINFORCEMENT (X) BELOW THE FINISHED SURFACE.
2. REMOVE ANY LOOSE CONCRETE PARTICLES AND DUST, AND THOROUGHLY CLEAN THE SURFACE.
3. PAINT CUT END OF REINFORCEMENT WITH ONE PART ZINC AND EPOXY RESIN (PARCHEM'S "NITOPRIME ZINCRICH").
4. PRIME THE ENTIRE SURFACE WITH AN ACRYLIC EMULSION BONDING AGENT (PARCHEM'S "NITOBOND AR" FOR HORIZONTAL SURFACES AND "NITOBOND HAR" FOR OVERHEAD AND VERTICAL SURFACES).
5. REPAIR THE REBATED AREA WITH A PREMIXED, NON-SHRINK, HIGH STRENGTH REPAIR MORTAR (PARCHEM'S "RENDERROC HB40").
6. ALL REPAIR PRODUCTS ARE TO BE USED STRICTLY IN ACCORDANCE WITH THE MANUFACTURER'S WRITTEN INSTRUCTIONS.
7. IF THE BUILDER PROPOSES TO USE ANOTHER MANUFACTURER'S PRODUCTS, THEY ARE TO SUBMIT FULL TECHNICAL DETAILS OF ALL PRODUCTS TO THE ENGINEER FOR APPROVAL PRIOR TO CARRYING OUT THE WORKS. SUCH PRODUCTS ARE TO HAVE SIMILAR CHEMICAL AND PERFORMANCE CHARACTERISTICS TO THOSE SPECIFIED.

Also include a diagram.

Please review because I am also seeking constant improvement on my standard procedures. 34' and 54' are big penetrations and I hope that you have performed the necessary analysis to prove that the walls can re-distribute the forces around theses openings.

 

[cvg]

if you can stand a square hole, use a concrete saw to do it instead of a core drill. Square hole is also easier to repair / reinforce than a round one.

 

[msucog]

34" and 54"? they'd be better off locating the steel in the correct place and blocking out the opening to begin with.

 

[rowingengineer]

If you going to use cvg advice make sure that core holes are placed at the corners of the square to stop crack propagation.

An expert is a man who has made all the mistakes which can be made in a very narrow field

 

[Schneidly]

The large diameter openings are at existing water treatment facilities. Pipes are penetrating the walls.

That is why we are cutting concrete instead of blocking it out.

Any more recommendations on the notes at saw cuts and large core openings in existing concrete?

 

[TXStructural]

Do not coat exposed ends with zinc-rich paint - it will try to act as a cathode for the entire bar. Use a barrier coating (epoxy is acceptable for this, as you are trying to use a barrier in lieu of concrete cover.) I am not familiar with the previously mentioned product, but would spec something like Sika Armatec 110 for this use.

It is unlikely that anyone can actually core 54 inches. The largest I have found is 36" diameter, and I am sure that is a truck-mounted rig.
You can see about a concrete cutting contractor that uses an ICS chain saw. I'm not sure they can do a radius, but 54" is not very tight and might work. They could readily do an approximation of round with a series of plunges.

But the most common solution is to core or hammer drill a series of holes around the perimeter and jack hammer the core out. Basically, draw the circle, drill 1-2 inch holes spaced 2-3 inches on center, and remove waste. If you elect to core the reinforcing as a means of cutting it, it may make the removal easier.

 

[asixth]

TXStructural

Are you saying that the third note I listed above is incorrect and that painting the exposed end of reinforcement will try to promote corrosion.

 

[Zambo]

asixth,

TXStructural is stating "exposed" ends. Your point 3 however is followed by points 4 and 5 by which you describe how the ends will be covered and therefore not "exposed".

 

[racookpe1978]

Get hold of a high pressure hydroblast company. (I've used one before south of Philly (near Eddystone power plant). These guys have ultra high pressure and slurry UHP portable water cutting equipment.

Mount two of their cutters on a bar or pivot. Brace it against recoil (backpressure) put the pivot on the center of your hole and slice the hole(s) you need.

Based on the structural advice above, it sounds like you need 4-6 inches larger dia hole than your pipe alone = your pipe + insulation + insulation jacket + movement clearance + installation margin + rebar cover concrete.

Kind of like a plasma cutter in real thick steel, the water jet cutters spread out a little bit the deeper you go - but it beats jacket hammers and saws and drills. I don't think you can get any core drill larger than 10 - 12 inches.

 

[TXStructural]

I'm saying that you should NOT use zinc-rich paint for spot coating of otherwise non-galvanized bar. The small area of zinc coating area will deteriorate rapidly as the remainder of the bar uses the zinc as a sacrificial cathode. You should use an alkaline-tolerant barrier coating (Sika Armatec 110, or similar.) You can also simply cut the bar back far enough that new cover is sufficient.

 

[csd72]

Have you notified your client about the potential cracking that these modifications may cause. That is the first thing you should do, otherwise it WILL happen and you WILL be blamed.

 

[Schneidly]

Why would saw cutting cause cracking? What can I do as the design engineer to limit the risk for cracking?

 

[csd72]

There is nothing you can do, thats entirely the point.

Wind, quake, temperature, load redistribution.

 

[hokie66]

Well, there is something you can do. Cracking is caused by stress, and reentrant corners multiply the stress. So if you are cutting a rectangular hole, coring the corners helps to limit the cracking caused by the stress risers.