Over the last few weeks, we have been in and out of several different sites where heavy
equipment was present. Not only was there heavy equipment, but there were heavy loads being moved by said equipment. While on site at two of these facilities, we witnessed what is known as a “rocking slab” and if not addressed, this can be a problem.
What is a rocking slab?
A rocking slab is a concrete slab with unintended movement as weight is transferred from one concrete pad to the next, also known as load transfer. The movement from the slab
is due to soil displacement or a void under the slab. In the case of both of incidents mentioned above, the rocking slab was due to a water leak on the opposite end of the property. Water flowed under the slabs taking soil with it. As the aforementioned slabs moved, any joint fill material was compromised and surface water began to find its way under the slab. As equipment traveled over the rocking slabs, water was forced back through the joints, indicating wet and weak soil conditions under the slab.
Expanding polyurethane resins (Polyfoam) are perfect for this scenario. In the case of both of these facilities, minimizing downtime is essential to their daily production. If each facility had to tear out and replace the slabs (which has already been done and has failed) they would have to wait days for the concrete to completely cure. They can drive on a Helms Polyfoam repair within 15 minutes. Polyurethane used for this repair is hydrophobic, which means it will displace moisture in the weak soil. The water leaks that caused the rocking slabs most likely caused issues deep within the soil, not just under the surface. Fortunately, Helms Polyfoam is able to address issues deep within the soil as well us just under the surface. In closing, expanding polyurethane resin is the perfect repair for a rocking slab. Soil can be treated deep under the slab, moisture intrusion can be mitigated, and load transfer can be achieved, all without shutting down production.