Polymer Geopolymer Injection & Hydro-Sealing for Residential Pedestrian Flatwork
Challenge
A residential pedestrian walkway in Cedar Rapids, IA, suffered severe differential settlement across multiple exterior concrete slab control joints. The primary mechanism of failure was identified as hydraulic subgrade washout beneath the slab-on-grade concrete matrix. Surface runoff penetrated unsealed joint lines, systematically eroding the fine-grained subgrade soil and creating localized sub-slab void pockets.
Lacking continuous, uniform base support, the concrete slabs sheared along existing stress lines under dead weight and foot traffic, settling into the subgrade voids. The resulting vertical offsets created vertical trip hazards and compromised accessibility for mobility equipment like walkers. The primary engineering challenge was restoring the flatwork to a level, stable elevation without employing heavy machinery, generating excessive dust or noise, or adding heavy material weight that could induce further subgrade consolidation.
Solution
To restore the structural plane without heavy demolition or prolonged cure times, System Design Specialist Shawn Conaway engineered a multi-stage lifting and hydro-sealing protocol using PolyLevel® Concrete Leveling and NexusPro® Joint Sealant. Operations Lead Ricky Sigala and field technician Jaylen executed the repair by drilling dime-sized injection ports through the settled slabs at calculated pressure points.
The team injected a high-density, hydrophobic two-part polyurethane foam beneath the concrete. As the geopolymer expanded up to fifteen times its liquid volume, it filled underlying voids, compacted the surrounding loose soil, and exerted upward hydraulic force to lift the sunken concrete back to a level plane. Following real-time elevation alignment, the crew routed open joints and applied UV-stable NexusPro silicone sealant across all seams, blocking future surface water infiltration. The injection holes were patched with matching cementitious grout, leaving behind a smooth, fully stabilized walkway that returned to service immediately upon project completion.
