Challenge

The Tennessee Department of Transportation (TDOT) observed 1,700 feet of the eastbound center lane of Interstate 24 had settled as much as two inches. More concerning about the settlement was the up to two inch differential between lanes that had to be navigated by motorists when changing lanes. This situation was a serious safety concern that had to be addressed immediately. TDOT specified the center lane be lifted back toward level and flush with the lanes on both sides. Due to the heavy traffic on this stretch of the interstate, TDOT required the work to be done during non-peak traffic hours (9 p.m. to 6 a.m.) and at least one eastbound lane needed to remain open throughout the job.

Solution

TDOT selected polyurethane injection to fill the voids and lift Interstate 24 back toward its original position. The polyurethane material 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 a slab or surface, a chemical reaction converts the liquid urethane components to a strong, rapidlysetting foam material. In its foam state, polyurethane 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), polyurethane can provide the necessary strength to support heavy loads.

Due to the quick-set nature of the polyurethane injection, the center lane was open to traffic once the traffic control was removed immediately after injection. A total of 9,268 pounds of polyurethane was injected through injection ports laid out in an approximate five foot grid pattern. The expanding polyurethane foam filled the voids and lifted the sag in the highway, as well as noticeably filling voids that were present under the adjacent traffic lanes. The entire project was completed in just three days instead of the five days allotted by contract.

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Project Summary

Certified PolyLEVEL Installers: Alabama Foundation Specialists

Products Installed: PolyLEVEL 400, High-Density Spray, Polyurethane by Foundation Supportworks Inc.

Product Characteristics: 100 psi compressive strength, 146 psi tensile strength, 69 psi shear strength, 19:1 expansion rate, 6 pcf typical in-place density