Making Swiss Cheese in concrete slab

[oceanobob]

My question has to do with using a hydraulic powered breaker on a mini-excavator or a backhoe. In the past we have tried the breaker on the backhoe and it made the slab look like swiss cheese, and it also (undesirably) pushed the concrete cone out the underside well into the subgrade, making the helper unhappy when they had to rake it out.
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So we decided we needed a smaller breaker so we asked the rental yard to equip the Kubota KX41-3 (2008) with a breaker. This is a machine with 'expando' tracks and a 'less than fascia board height' rollcage. Guess what - it can make swiss cheese too!.

To explain, the tip punches a hole in the slab, there are no cracks emanating outward and we have repeatedly read Do Not Pry or You Will Cry. We end up with a slab that has all these holes, it is quite weakened and pulls up in chunks when one goes back over it with the toothed bucket. Is this the typical result or is there a technique we are missing? And yes the cones are pushed into the subgrade. If we operate a pavement breaker we get sore and the concrete breaks without punching through. We peel off chunks like peeling an onion.

I enclosed photos, but I neglected to show the swiss cheese effect.

FYI The job was to remove these "forklift ramps" that were to enable traversing the 18" step in the floor slab elevation. They weren't necessary since the forklift can accomplish the same by driving outside which is ramped, not stepped.

 

[Hendrik]

Breaking concrete can be a laborious exercise, especially if it is reinforced.
The thing is to have a space where the concrete can break into, if it has nowhere to go you will end up with 'Swiss cheese' another mistake that people make is to try and break off too much. Say you got a m2 patch of concrete, you stick the tool in the middle and you'll end up putting a hole in it, put the tool about 20cm from the edge and it will break of a sizeable chunk. OK so you'll have to have a few bites at this m2 piece of concrete but you are doing what you set out to achieve, instead of trying to break off bigger pieces and end up wasting time.
Although not always possible, I think it is recommended to use a blunt face tool for concrete, this does the job of cracking the concrete rather than punching through it.
http://hkm1987.trustpass.alibaba.co...034440/Chisel_For_Hydraulic_Rock_Breakers.jpg the one on the left is the concrete one
Another trick the big boys use is to have two machines, one to bash the concrete and another one with a grab to take the broken stuff away. Although on a small machine with two people it is pretty quick to drop the breaker (I usually drive the breaker into the ground and stand it up) and pick up a bucket. A thumb comes in handy too.
Lastly if you got a machine with a backfill blade, put the blade out the back and use it to get extra weight on the breaker.

 

[buckfever]

Like hendrik said that is pretty common. We had the same problem tearing out some diveways with wire mesh. We ended up cutting sections with a chop saw and lifting them out with forks on our skidloader.

 

[Dozerboy]

When there is sand for subgrade there isn't much you can do. I will load out some of the sand in order to make it easier on the groundmen. The skill of the operator plays a big roll here.

You didn't need a smaller breaker like with lots of things bigger is better. You just needed to use less "whacks". Our big hammers will bury the bit through the road in 6 whacks, so I will only use 3/4. Sometimes there isn't much of a hole, but I know the breaker has already done its damage. Its all about trial and error and knowing what it takes to break the concrete up enough it comes apart, but not so much it makes a mess.

 

[Hendrik]

You didn't need a smaller breaker like with lots of things bigger is better. You just needed to use less "whacks". Our big hammers will bury the bit through the road in 6 whacks, so I will only use 3/4. Sometimes there isn't much of a hole, but I know the breaker has already done its damage. Its all about trial and error and knowing what it takes to break the concrete up enough it comes apart, but not so much it makes a mess.

Well yeah, bigger machines do more work but cost more to run. Depends what you have access too.
In the scheme of things this was not a huge job, if the contract was to rip the entire floor up then I would think a couple of bigger machines would be more cost effective, one to break and one to rip the concrete and load it.
Do you use a flat concrete tool on your breaker?

 

[245dlc]

Your other option if you do enough of this kind of work is saw cut the concrete into 'manageable' sections as in what the machine can lift and use a set of forks (not always recommended as I've seen a few break) or get a pavement removal bucket where you can slide it underneath the slab and lift out sections at a time.

http://www.rocklandmfg.com/index.php?page=pavement-removal-excavator-buckets

 

[BlazinSS934]

You can also check out heavy equipment forums very good site


Sent from my iPhone using Tapatalk

 

[Wolf]

Awesome answer, John. You can tell this operator really knows what he is doing! How's it going, man? Good to see you on here.

 

[oceanobob]

Thanks, these ideas have helped out. In this case the subgrade being sand didnt upset the laborer too much, but the next one is on clay and it can be a bit of a dilemma to dig out cones.
There is no doubt the operation of the breaker is as usual like most things more than meets the eye.

 

[blowerman]

When we are removing concrete from inside buildings, we have it cut into 3x3 or 4x4 pieces. To get a starter, we make two holes with a hammer drill, then drop rod into the holes, wrap with chain and pop out a section. This takes all of 5 or 10 minutes, then the rest is taken out with forks on a skiddy. I've removed lots of concrete in my life and this is one of the fastest ways we've come up with.

 

[joispoi]

Bob, I see more broken up concrete in those pictures than anything that could be mistaken for Swiss cheese. It looks like you're doing just fine. What's been said above is true. The concrete needs a place to go when it fractures. Don't use the hammer on any one spot for more than 15 seconds. Don't try to break off too much at once. If you've ever had to split a concrete block with a mason's hammer, you know that you have to work along the line where you want it to crack. Try moving the hammer more often and move it shorter distances. Once it starts to penetrate, move along the line where you see/want it to crack.

 

[Dozerboy]

I forgot to add. It doesn't really need a place to go when it breaks. When we to roads I'll put holes on 2' centers like grid work swinging side to side and them tracking back 2'. I never crowd its faster. By breaking it that way the concrete will crack between the holes and it will come out in chunks 2' and less. This depends on the size of your iron we normally use a 30 ton hoe to pull the concrete. Rebar changes things you can do it like that but its dangerous however easier to clean up. You need a saw or a torch to cut the bar at times. Its easy with rebar if you pulverize like the OP did in his pics then I will pull it out with a hoe wad it up into a ball.

 

[Trevor Wrench]

Stanley makes a skid steer attachment called a Cyclone, it is a drop hammer and it will ruin a slab up to a foot thick!! http://www.stanleyhydraulic.com/Products/DHSeriesDropHammer/tabid/122/Default.aspx

 

[CM1995]

Your other option if you do enough of this kind of work is saw cut the concrete into 'manageable' sections as in what the machine can lift and use a set of forks (not always recommended as I've seen a few break) or get a pavement removal bucket where you can slide it underneath the slab and lift out sections at a time.

When we are removing concrete from inside buildings, we have it cut into 3x3 or 4x4 pieces. To get a starter, we make two holes with a hammer drill, then drop rod into the holes, wrap with chain and pop out a section. This takes all of 5 or 10 minutes, then the rest is taken out with forks on a skiddy. I've removed lots of concrete in my life and this is one of the fastest ways we've come up with.

The quickest and cleanest form of concrete slab removal is the two methods posted above. If it's possible to saw cut the slab into small pieces instead of hammering, I will always go with that option. Cut the concrete into squares that whatever equipment you are using for removal can handle it.

Saw cutting can get expensive but so can running a hammer. I sub out my saw cutting on demo jobs, it's easier and cheaper for me to do this instead of owning a slab saw and using my guys.

I know this is an old thread but techniques are timeless. Oceanbob, I would have cut those sections and removed them whole. Use the forklift in the picture to lift the slabs out once you got the first piece out. I think it would have been cleaner and quicker using this method. The upside to cutting in squares is the concrete can be recycled into retaining wall material.

 

[oceanobob]

The other day I had to take out about 7 yards of residential flatwork in the back of a house with limited side yard access....about 500 to 600 sf. We ran the breaker mini excavator 'only' because we have to rent it and there was a short piece of garden retaining wall and a two riser solid concrete stair and the saw was not possible to solve the removal of those two things. So, to get the utilization out of the daily rental fee, we did it all with the mini and breaker. It took 6 hours to break it up and 18 man hours to load it into the containers using laborers and wheel barrows.

We actually got lucky since two thirds of the job were without any reinforcing but one third was wire mesh fabric. This mesh 'slowed the breaker' and made for many smaller pieces.

On the other hand, if we had hired a "high horsepower saw" (faster cutting speed) company to first cut it into pieces, then we would have been able to to use the forks on the dingo ....

My first inclination is to break it up, but the sawing into squares is something I am coming around to.

 

[BDFT]

I try to break it into squares but it depends a lot on what the strength of the concrete is and how much rebar/mesh is in it.
https://www.heavyequipmentforums.com/showthread.php?22838-Breakin-concrete&highlight=

 

[robin yates uk]

the Swiss Cheese affect is cause by using a thin chisel which encourages multiple holes, minimal breaking of rebar or wire and is in my opinion a waste of time.I have done great deal of breaker work, mostly in works environments where lorry access has to be maintained.A thick chisel like fitted to a Montebert 125 or 250 breaks and cracks the concrete, and a hard crowd to break the rebar at every hole is essential.This leaves a surface with no steel showing and still crossable with rubbers.Plus if the ground underneath is wet you can still load the trucks without chewing up the subfloor as the plant is still standing on concrete The idea of using big sawcuts is laughable as the rehandling must be dangerous and very time consuming

 

[CM1995]

The idea of using big sawcuts is laughable as the rehandling must be dangerous and very time consuming

Really? Have you ever used that method before?

 

[robin yates uk]

Really? Have you ever used that method before?

I have never seen this method used in the UK but have watched UTube vids,,,,,,,,,seems to be labour and machinery intensive when compared to a big breaker and competant workers.

 

[CM1995]

I have never seen this method used in the UK but have watched UTube vids,,,,,,,,,seems to be labour and machinery intensive when compared to a big breaker and competant workers.

The method can be very effective and safe. I have removed 1000's of SF this way from inside buildings to parking lots. Several years ago we did a restaurant remodel that required removing the entire slab inside the building, about 1500 SF. Saw cut the slabs into 3x3 squares and put the mini-ex inside the building. This was a wood framed building so we removed a section of exterior wall and shot the boom of the gradall inside. Used the mini to stack the slabs on the forks and then placed the slabs in dump truck with a high lift gate in the up position. We had the slab demo'd in less than a day and the plumbers were inside running the new piping the next morning. The GC had allotted 3 days to remove the slab and the super was amazed we got it done that quick, as he had never seen it done that way before.

I have also done several parking lot repairs the same way. The trick is to have the saw cutter cut a keyway in each area to be removed so you can lift the first piece out. The keyway is basically a small saw cut section of concrete you can lift out by hand in order to get the bucket teeth under the first slab to lift out.

This method is safe when using a thumb on an excavator or grapple on a skid steer. Sometimes it takes two machines to do the removal, one to lift the slabs out and one to cart them but using a hammer also takes two machines or swapping attachments to get the broken concrete out.

The saw cut method will beat hammering hands down in the right situations, with less clean-up time. When you are lifting 9 SF (3x3 squares) at a time, the production can't be touched with a hammer and the associated clean up time of picking up the pieces. Thickness of the slabs obviously dictates the size of the squares and the production rate. Slab thickness from 4" to 8" can be handled effectively this way. When the depth exceeds 8" or it's heavily reinforced then one has to compare the cost of saw cutting to using hammer.

Another plus to the saw cut method is you end up with a usable product. We haul the slabs back to the shop if it's close enough. The slabs are used to build retaining walls and have people from time to time buy them for that purpose, so it's a double dip. Our State regulations allow concrete to be used as beneficial fill if there is no wire or rebar protruding from the concrete. By saw cutting this fixes that issue and if it's not cost effective to haul the pieces to the shop, we can dump them at an inert site for much cheaper than a landfill.