Brace Hall is a 110 year old, three story structure sitting in the shadow of Memorial Stadium on the University of Nebraska campus. During recent renovations, the general contractor was alarmed to discover large voids under the main floor slab. Research indicated a concrete tunnel was constructed under the slab and it was determined the voids were a result of the concrete tunnel absorbing all of the moisture in the soil beneath the slab. Even though the floor had yet to settle, there were concerns about the probability of that happening after the building was fully renovated. Because this project was on a tight timeline and the void was both unforeseen and unbudgeted, resolving this issue quickly, effectively and affordably were the key factors in determining how to move forward. Concrete replacement was far too disruptive and costly. Filling the void with concrete slurry would add significant weight on the base soils as well as the very old tunnel structure potentially causing future soil settlement or even tunnel collapse.

Because of the speed of install and the minimally intrusive nature of the solution, FSI by Thrasher was selected to install PolyLEVEL™ 400 (PL400). PolyLEVEL™ is a two-part urethane that expands into a rigid foam used to fill voids, stabilize slabs and lift concrete. Once injected through small 5/8-inch drilled holes in a slab or surface, a chemical reaction converts the liquid urethane components into a strong, rapidlysetting, waterproof foam material. In its foam state, PolyLEVEL™ is very light, typically weighing between two and six pounds per cubic foot (pcf) yet having an astounding compressive strength of over 14,000 pounds per square foot. Other void-filling or lifting materials can weigh up to 120 pcf, adding significant burden to supporting soils or subgrade structures and potentially contributing to further settlement. FSI by Thrasher installed 6,103 pounds of PL400 product over three days with no disruption to the other trades performing their work.

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