Slab Curl Repair
Slab curl or warping results from uneven curing of the top and bottom surfaces of a slab floor, particularly after control joints are cut. Sometimes the curl is extensive enough to see, but usually it’s very slight (just a few hundredths of an inch). The functional problem with slab curl & warping is that the slab is no longer in uniform contact with the underlying ground. In lightly loaded structures, this generally doesn’t cause problems. However, for floors subjected to high loading from large material handling equipment, the lack of uniform support can quickly lead to movement and then cracking and deterioration.
Signs of Slab Curl
One of the easiest signs of slab curl to identify is clicking or thudding noises when material handling equipment crosses over a joint. In cases where the curl is significant, it’s usually possible to see the slabs move when wheel loads cross the joint. Spalling and deterioration at joints can also point to slabs rubbing against each other during movement (even too slight to see). Lastly, cracking due to slab curl is rather characteristic, and is usually starts with a crack parallel to the affected joint (transverse to traffic). Once the cracks develop, the curled section generally drops down onto the underlying material and the click & thudding stop. However, unless undersealed, the cracking and deterioration generally continue if not addressed by undersealing by polyurethane grouting.
Floors with embedded guidance systems crossing curled joints often suffer from frequent breaks of guidance wires at joints due to the flexing applied to the wires as a result of movement across the joints from dynamic loading.
Slab Curl Repair Method
The first thing that needs to be addressed with slab curl is stabilization of the slabs to stop movement. To do this, material is injected into the voids that are formed as the slabs curl or warp up off of the underlying base material. We use high density polyurethanes for this. The polyurethane foam is injected through small holes drilled in the slab, and spreads out to fill the voids. This restores the slab to uniform bearing. We use special undersealing foams for this work that are design to fill even the smallest voids without lifting the floor.
Tolerance for undersealing is generally under 0.05 inches. Undersealing to establish uniform bearing stops slabs from rocking with dynamic loading and restores stability.
If there is also differential movement at a joint (one slab is higher than the other), lifting foam can be injected to restore an even transition between slabs.
Once slab movement has been addressed by polyurethane grouting, any spalls and deterioration can be patched as required. Depending on the extent of damage, selective replacement may be required.
Slab Curl & Flatness
There are two general functional problems associated with slab curl. The first, and most common, is the instability of the floor caused by flexing under dynamic loading. This can lead to slab deterioration & excessive wear on equipment tires. The only way to fix this is to fill the slight voids below the slab caused by it lifting up off of the underlying soil as a result of curling or warping.
The second functional problem with slab curl is changes in the surface profile. The flatness of floors is quantified using the F-number system. F-numbers are used for static assessment of how flat a floor is, and are not designed to quantify movement from dynamic loading. Most commercial and industrial floor slab curl is slight enough that the resulting surface waviness does not cause toppled loads, lost connection to guidance systems, etc due to vehicle movement. Some curl is significant enough that it can result in functional problems such as toppled loads, or low-clearance equipment getting hung on joints.
Addressing deviations from flatness standards is a separate repair from stabilizing movement. Flatness is addressed by grinding or polishing. Grinding or polishing do nothing to address movement.