Concrete Sidewalk
Concrete Sidewalk
(OP)
I am trying to repair a concrete sidewalk which is approximantly 400' long. Currently various sections of the sidewalk are breaking apart and becoming uneven. My orginal plan was to remove exiting sidewalk and soil beneath. Then refill excavated area with compacted sand (95% dry density) and repour a new sidewalk. New Sidewalk would be 4" thick with #4 rebar at 12" O.C. in both directions. New sidewalk would have control joints every 5'.
It has down been proposed that we should instead pour a new 4" thick sidewalk with rebar on top of the existing. I am concerned that this will result in future probelms. Any comments or suggestions.
It has down been proposed that we should instead pour a new 4" thick sidewalk with rebar on top of the existing. I am concerned that this will result in future probelms. Any comments or suggestions.





RE: Concrete Sidewalk
Based on our City's experience possible reasons include: tree roots, sewer lines, other utilities, and freeze/thaw action.
RE: Concrete Sidewalk
Generally no need for rebar. Plain concrete is fine for this application. Most common cause of cracking in sidewalks is the items GPT mentioned plus poor thickness control/poor quality control during construction.
For a thin slab such as this, it is critical that the subgrade be flat and that very little thickness variation occur. Sawcut the joints the same day as placement. Spacing is right for 4-foot width.
RE: Concrete Sidewalk
Ron you basicly confirmed my intial concerns that the cracks would resurface in the new concrete pour.
RE: Concrete Sidewalk
Again, be sure to specify quality placement processes and controls...that will alleviate many of the problems.
RE: Concrete Sidewalk
Another thing that came to mind, is there any chance that the damage was caused by someone driving on this section of the sidewalk? I know you don't normally drive on sidewalks, however, I have seen it many times. People are just in too much of a hurry.
RE: Concrete Sidewalk
The sidewalk is in fact driven over by large tractors when they cut the grass field surronding the sidewalk. This is why the rebar will be installed in the new sidewalk.
A second question: If contractors where to install expansion joints instead of control joints what is the typical spacing for a 4' wide sidewalk.
RE: Concrete Sidewalk
Just because the landscape tractors drive on the concrete doesn't mean it needs to be reinforced. If the subgrade is appropriately stable and compacted, those loads shouldn't be much of a problem for a 4-inch thick slab as the contact stresses are low and the total load is not that high either.
RE: Concrete Sidewalk
If it is being driven over by a "tractor" a minimum thickness of 200mm with F92 top and bottom would be approppriate.
F92 = deformed bar mesh with 9mm diameter bars at 200mm spacing.
Also soils are not just soils, they are sand (fairly stable) silt (slightly reactive) and clays (will react to moisture swell shirnk, etc). This will effect the design.
Also always dowel joints where movement is expected as it keep the footpath (sidewalk) together when it moves.
regards
sc
RE: Concrete Sidewalk
A #4 rebar in the US is 4/8 of an inch or 0.5 inches in diameter.
RE: Concrete Sidewalk
Remove damaged sidewalk, investigate reason for heaving or depression. Remove reason, fill material, and recompact with new granular fill.
RE: Concrete Sidewalk
I see this as a significant cause of damage.
In time, the water softens the soil causing erosion and the softenting of concrete leading to cracks.
Other than that, it is pipes or roots beneath the soil.
Regards,
RE: Concrete Sidewalk
When you place the new sidewalk, be sure to rope it off and keep traffic off of it for at least 7 days...