Florida State University (FSU) commissioned the repair of an area of interior concrete slab-on-grade at the first floor level of the Kuersteiner Music Hall. The 200 square-foot area of slab had settled differentially as much as 1.5 inches over 10 years due to consolidation of loose fill soils below the slab. The slab settlement affected the operation of doors and caused cracking within interior drywall and concrete block walls. Project specifications stated that the repair include filling of all voids and lifting the concrete slab back to level, thereby closing cracks in the walls and making the doors operational. It was also necessary to complete the project within the narrow allotted window of only one day in order for the area to be prepared in time for the fall semester.
FSU selected PolyLEVEL™ polyurethane injection to fill the voids and lift the slab back toward its original position. 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 “ports” in the slab, a chemical reaction converts the liquid urethane components to a strong, rapidly-setting foam material. In its foam state, PolyLEVEL™ is relatively light, weighing two to six pounds per cubic-foot (pcf). Other void-filling or lifting materials can weigh upwards of 120 pcf, adding significant weight to supporting soils or base materials and potentially contributing to further settlement issues. With a compressive strength of 100 pounds per square-inch (psi), PolyLEVEL™ can provide the necessary resistance to support even heavy loads.
Small, badly broken areas of concrete slab were saw-cut and removed. Through these penetrations, the void under the slab was observed to be much larger than anticipated. The void was several inches tall and extended outward beyond the specified repair area approximately 15 to 20 feet in all directions. A total of 600 pounds of PolyLEVEL™ 400 were injected through ten injection ports laid out in an approximate five-foot grid. The expanding foam filled the voids and lifted the slab approximately 1.5 inches, realigning the doors and closing cracks in the drywall and block walls. Sections of removed slab were replaced with new concrete. The entire project was completed in just six hours.