An Atlanta-area distribution center was experiencing a decrease
in productivity. The culprit: rocking and thumping floors. Thinking
they were in for some extensive rennovations, including tearing
out and repouring the troublesome slabs, the maintenance manager
called on the warehouse owner to fix the problem. Luckily for
everyone involved, the owner of the property was aware of grouting
as a soultion.
The production area of the facility was the area with the most
audible "thumping" sound every time a forklift rolled
over a floor joint. The problems were caused by "curling"
of the concrete slabs at the joints. Curling is a common problem
with concrete slabs that occurs during the concrete's curing process.
As the newly placed concrete cures, the top surface (exposed to
the air) cures and shrinks more quickly than the bottom surface
that is in contact with the soil. The result is that the edges
of the slab curl upward from the subsurface. This leaves a small
void under the edges of the slabs at each joint. When a heavy
forklift rolls accross a curled joint, the concrete edge along
the joint under the forklift tire flexes downward. Then the forklift
tire strikes the higher concrete along the edge of the other side
of the joint. While the immediate result is an audible "thump,"
the concrete along the edge of the joints will eventually crack
and spall because of the repeated flexing and abuse.
The voids underneath the slabs in the distribution center could
potentially be extensive, so the concrete contractor decided to
use Prime-Flex 985 due to its 10:1 expansion rate and high compressive
strength. Prime-Flex 985 is a two-component urethane resin that
produces a strong, lightweight, highly cross-linked rigid structural
foam. Prime-Flex 985 can provide significant slab or structural
support without the added weight loading of traditional cement
grout stabilization.
The repair took several weeks with the repair crew working only
weekends to accommodate the schedule of the distribution center.
Once completed, the distribution center manager immediately noticed
an improvement in the slabs. "The thumping noise has stopped
and you can stand on the joint (between two slabs) without feeling
any rocking," he said. Over time, it will be possible to
measure the benefit of this repair by analyzing forklift maintenance
costs and rates of productivity.
A typical joint showing wear due to a void under the slabs.
A void underneath two slabs at the joint will cause the
joint to become misaligned. Eventually, the edge of the
joints will crack and spall because of the repeated flexing
and abuse.
Prime-Flex 985 is injected through holes drilled
into the concrete to fill the voids. Once the void is filled,
material will expand out of the drilled holes, sealing them.
The excess grout is then cut off the slab and the hole is
sealed with Prime Seal 5800.
