Concrete Patch Repair
Concrete Patch Repair
(OP)
I haven't really done any concrete repair work in my career until now, so I am looking to get an opinion on concrete patching details. In my specific case, I have 7 areas on a concrete pedestrian bridge that have spalled and need to be repaired. Each spall is approximately 14 inches by 14 inches and is about 4 inches deep, and all are located at the transverse edges of the bridge. The overall thickness of the bridge is 9 inches and it is lightly reinforced with #4 transverse bars at 12 inches o.c. top and bottom. There are no longitudinal bars where the patches will be. The bridge is located in Minnesota. The spalls all occur around existing guardrail posts that are embedded in the concrete. We will be removing and replacing the guardrail posts with surface mounted posts, and we will be moving the locations of the posts away from the patches.
I have included the typical patching detail that my previous employer used. Yesterday (1-19-18) someone posted a whole bunch of details from the New York City Transit Authority. Similar details were found in that set.
One of my questions is, why do some details include a series of anchors embedded into the existing concrete (identified as "D" in the attached detail) with a layer of welded wire fabric (identified as "C" in the attached detail) attached to it, and other details do not include any new reinforcing? I don't believe these bars are for strength because they aren't properly lapped with the existing bars nor would they be the same size. Are they for temperature and shrinkage? Do large patches contain this reinforcing and small patches don't?
Also, what type of patching material would be the best to use? I have read up on latex modified concrete, epoxy modified concrete, and concrete carefully designed to control shrinkage. I am leaning on going with carefully designed concrete because it can be placed in one lift and the fact that the other products requires a more skilled laborer to execute. Do you agree/disagree?
Any comments would be appreciated. Thank you!
I have included the typical patching detail that my previous employer used. Yesterday (1-19-18) someone posted a whole bunch of details from the New York City Transit Authority. Similar details were found in that set.
One of my questions is, why do some details include a series of anchors embedded into the existing concrete (identified as "D" in the attached detail) with a layer of welded wire fabric (identified as "C" in the attached detail) attached to it, and other details do not include any new reinforcing? I don't believe these bars are for strength because they aren't properly lapped with the existing bars nor would they be the same size. Are they for temperature and shrinkage? Do large patches contain this reinforcing and small patches don't?
Also, what type of patching material would be the best to use? I have read up on latex modified concrete, epoxy modified concrete, and concrete carefully designed to control shrinkage. I am leaning on going with carefully designed concrete because it can be placed in one lift and the fact that the other products requires a more skilled laborer to execute. Do you agree/disagree?
Any comments would be appreciated. Thank you!






RE: Concrete Patch Repair
My experience has been great using a few simple steps.
Rattle off as much of the weakened concrete as possible with small jack hammers or similar. A riveting gun with chisel works. The surface left should be sound concrete,if possible and LEAVE IT DRY!!! Never add water. If weather is wet, use a flame or similar dryer to get rid of all moisture at AND WITHIN that surface.
Vacuum or blow off all dust.
Brush on a paste consistency of Portland cement and water. Work it into the dry concrete, the object being the dry concrete takes this on by capillary action. This is the glue, keep it thin.
Follow immediately with as stiff a concrete mix as possible.
Cure as you would regular concrete (moist).
If you wish, wait a few weeks and drill a core sample to see how you did. Then try to break it with a chisel at the bond.
RE: Concrete Patch Repair
RE: Concrete Patch Repair
Besides that, their representatives are knowledgeable and helpful. If they don't know something, they call their technical experts in New jersey and get the answer.
RE: Concrete Patch Repair
One thing with deck repairs, it's possible that your partial depth repairs could end up going full depth.
RE: Concrete Patch Repair
RE: Concrete Patch Repair
RE: Concrete Patch Repair
RE: Concrete Patch Repair
One other thing to keep in mind, speaking from my field experiences: Concrete repair quantities have been known to overrun.The quantity that you will show in your plans is something that should be discussed with your client. If you feel good about your number a 25% contingency is not unreasonable. On one project I did a few years ago, the client told me to triple my quantity because of a bad experience they had on a recent project.
RE: Concrete Patch Repair
If you want to use a different material such as a polymer modified concrete, consult with Sika as JedClampett noted. They still require good preparation in accordance with the manufacturer's instructions, but are a bit more forgiving.
RE: Concrete Patch Repair
In a horizontal application, mesh might be warranted if you are using a manufactured product with a fast strength development in a deep patch. The mesh would help prevent shrinkage cracking for hot mixes. This was a problem with latex modified patching materials in the 80's & early 90's but the manufacturers have gotten better at mix design. If you go the manufacturer packaged route be sure your patching material has a compatible modulus.
Cement slurry returned to popular use towards the end of the 90's and is in many cases the best way to bond a patch but timing is important, as you don't want to cover more area than you can place patching material before the slurry sets up or dries out too much. Not all latex bonding agents are the same. If they are designed to be applied & used in a wet condition, they will have good bonding & water resistance but if they are of the apply and let dry variety they may not hold up to water ponding (bird baths). Some materials have powdered latex mixed in with the patching product. Again not all of these products are good in the frequently wet conditions. Sika & Master Builders would be safe choices.
It is better to be a hovering presence when the work is done the first time, than to be back in two years correcting the patches where the cement mason, re-tempered the mix.
RE: Concrete Patch Repair
I do have a couple questions about the cement slurry though: if the existing surface is properly prepared (roughened, cleaned, dried) won't the new concrete sufficiently bond to it without the slurry? Also, if I am requiring them to apply the slurry, what consistency (1 part portland cement, 1 part water?) and thickness is recommended?
RE: Concrete Patch Repair
RE: Concrete Patch Repair
RE: Concrete Patch Repair
RE: Concrete Patch Repair
edit: I'd be sure by not allowing a water hose on the job.
RE: Concrete Patch Repair
RE: Concrete Patch Repair