Outdoor Court Repair 1

[tclat]

Hi All,

I looking at repairing an existing outdoor basketball court with a slab on grade. The court is several decades old and the surface has started to deteriorate. The school does not have the fund to rip out completely and redo. I'm proposing the following

1. Roughen surface using light jack hammer and remove all loose concrete and thin temporary patches
2. Pressure wash surface
3. Moisten surface and place 2" concrete topping (consider it bonded) with no reinforcement. Topping will be placed at 1% fall along the short side of the court for drainage.
4. Sawcut control joints to match existing and fill in with joint filler. Add additional control joints to keep bays a maximum 12 feet c/c
5. Moist cure for 7 days.

I understand that any existing cracks will probably come up through this new surface.

Any additional thoughts or concerns? Should I consider a light wire mesh?

Thanks

 

[Ron]

Don't use a jackhammer....use a bushhammer or hydrodemolition....other than that, your approach is good.

You might consider the following as additional:

1. If you want to put additional control joints in the 2" topping, they need to be closer than 12 feet. That's appropriate for a 6" slab but needs to be closer for thinner slab. That's for top shrinkage of a bonded slab....will do nothing to control reflective cracking.
2. You might consider an unbonded topping....put a membrane between the existing and the new and set control joint spacing based on thickness of the topping. With that you will not have to match control joints with the lower slab.....you also will not have to prepare the older slab as much. The topping thickness should be at least 3 inches for this application and minimal reinforcing may be used to help control shrinkage cracking. I would not use wire mesh in such a thin slab. Place No. 3 or 4 rebar at 8 to 12 inches on center each way to mitigate shrinkage cracking.
3. Make sure the mix design of the concrete is compatible with the application. Use the larges aggregate possible for the thickness to minimize shrinkage.

 

[oldestguy]

Sorry but you would be making one BIG GOOF by wetting the roughened surface. Once roughened,vacuum clean the surface. USE NO WATER IN THE ROUGHENING EITHER UNLESS YOU WAIT ABOUT A WEEK OF DRY WEATHER before proceeding. Use no water thereafter unless it is to help cure the overlay. Just minutes prior to placing the concrete overlay (it probably should be a mix with pea gravel as the largest aggregate), you brush in a cream consistency of Portland cement with a little water. That will then adsorb into the pores of the old slab as a glue. Immediately place the overlay concrete with as stiff a mix as possible. When things have been damp cured a least a week or more, check your work by coring out a piece and check the bond. Do this with a chisel at the bond and try to break it there. My bet is it won't break there. For the whole court, you probably will have to do it in sections because you do NOT want the Portland cement cream to do much of any setting before the overlay goes on. That cream layer needs to be only enough to cover the old concrete. If the roughened surface has been rained on, make sure it is bone dry before proceeding. You want that cream to be soaked in.

 

[oldestguy]

I seldom differ with Ron. I only have done the procedure shown at parking garages where salt has damaged the surface of the slabs. The removal there might exceed an inch or so. Then, after curing it gets auto traffic. If there instead would be a plastic sheet, I would suspect the overlay won't handle it. Thicker, yes, but how much? In my case the salt damaged concrete has to be gone.

 

[Ingenuity]

...because you do want the Portland cement cream to do much of any setting before the overlay goes on.

You mean “...you do NOT want...”

 

[Ron]

OG...I agree with your approach. Hydrodemolition would be fine but agree that the surface should be dry before doing a portland cement paste bond. That's a good procedure and it works.

To prevent reflective cracking, I would go with an unbonded topping though.

 

[dik]

Interesting issue... a 2" topping does not work well if it's unbonded... I think you have to live with and address the reflective cracking that will occur. Hydrodemolition, a dry surface and wet curing are the way to go.

Dik

 

[oldestguy]

INGENUITY: Thanks a bunch. My moniker is my only excuse.

 

[XR250]

Ok, I am no expert here, but if you are going thru all the trouble to prep the existing surface and then put a 2" layer on top, why not just place 4" of concrete with shrinkage reinforcement on top of what is there? Seems it would be cheaper than doing all the prep work. I guess having to step up 4" may be an issue, but not much worse than 2 or 3".

 

[SlideRuleEra]

Topping will be placed at 1% fall along the short side of the court for drainage.

Is that the slope of the existing surface?
Assuming the surface preparation of existing concrete is of uniform thickness, the new topping will have to match the existing slope, or not be a constant thickness. Do the math, 1% slope is a lot compared to a 2" thickness.

Suggestion: After deciding on a final repair criteria, revisit repair cost versus replacement. We applied "thin" topping to repair existing concrete in the 1980s. In the end, did not save anything (probably cost more considering time it took) and never performed properly.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[oldestguy]

Ya can't beat the info from Slide Rule Era. Make a check on renting a scabler. My rough check was $105 a day. Then can a few of the larger kids or their dad's be involved with applying the cement paste and brushing it in? Cheap labor? A good sized shop vacuum may well do the vacuuming job.

 

[hokie66]

I always hated playing on concrete courts. Have you considered a bituminous overlay?

 

[dik]

Ya... it's softer...

Dik

 

[dik]

If you use a scabbler... best to wash it down and brush it off...

Dik

 

[oldestguy]

I'd do some research on just what you are in for roughening up the surface. This ain't any super highway with heavy traffic, but a simple slab not carrying any weight of consequence. The use of high pressure water jets sufficient even to remove sound concrete is not something I'd do. It also require a significant delay to dry out that prepared surface before proceeding to "glue" on an overlay. When it came to treating parking garage slabs, vacuum of the dust was the way. No way to get that dust into the drains system. Take time and have a plan without unknowns.

 

[BridgeSmith]

If the existing slab is at least 6" thick, mechanical scarification (that's what we call it for bridge decks) could be used to roughen the surface. For a slab less than 6", I'd be hesitant to subject it to the beating it will take roughen the surface with a mill. I'd suggest hydrodemolition to roughen the surface of a thinner slab. After roughening, we use concrete overlays as thin as 1" using silica fume modified or latex modified concrete for our bridge decks. In our region the silica fume concrete has gotten very expensive lately (up to $5000/CY in place), but it doesn't require prepping the surface with the cement paste. Because of the cost of silica fume, we're trying out a polyester concrete mix for our repairs and overlays. We also use 2" asphalt overlays fairly often with good results. If they'll hold up to truck traffic, they should handle foot traffic without any issues.

I suggest talking to your local ready-mix concrete suppliers and see what options they have and the prices, then talk to a couple local asphalt paving contractors about a 2" asphalt overlay. My guess is that asphalt will be much cheaper, unless most of your labor for the concrete work is done by volunteers, and the asphalt might still be cheaper.