An Expert's Playbook For Putting Concrete Back On Grade With Geotechnical Foam. 

Concrete doesn’t settle "just because". It settles when subgrades lose modulus from fines migration and water pathways, when approach slabs bridge over under-compacted backfill, and when thermal and dynamic loads concentrate at joints until contact is lost. Polyurethane foam injection is uniquely suited to reverse that trajectory. Done correctly, it restores uniform support, re-establishes load transfer, and returns assets to service in hours—not days, with minimal disruption.

THE APPLICATION

A geotechnical polyurethane used for concrete lifting and void filling should travel to the edges of the voids before elevating the slab, knitting cavities together for uniform contact. It should cure to a closed-cell, hydro-insensitive matrix that resists water uptake and maintains properties in damp or saturated soils. And at the installed density, it needs sufficient compressive strength and stiffness to re-establish bearing and load transfer across the slab with controlled elevation.

In practice, that points to water-blown, closed-cell systems with predictable cream/gel windows and strong dimensional stability in service. For precision slab lifting and joint matching, mid-density formulations in the 3–6 pcf free-rise class are common. For big cavities, low-exotherm void fills are used for extended travel and efficient volume recovery at lighter installed densities. The application dictates the formulation, not the other way around.

WHERE POLYURETHANE SHINES

Anywhere elevation tolerance and uptime matter: bridge approaches and departures, highway and street panels, airport taxiways and aprons, curb-and-gutter transitions, sidewalks and driveways, and foundations. The footprint is small—ports are typically ∼5/8 inch—and the method works in live environments that can only spare brief shutdowns. For owners, that means less disruption and faster reopening. For contractors, it means a controlled, meter-by-meter method that scales.

FIELD-PROVEN WORKFLOW

•  Map & Plan: Begin with subsurface intel. Probe or scan to map the void boundaries and soft zones. Set acceptance up front: target elevation tolerance and a reopen time based on cure.
•  Grid & Sequence: Lay out an injection grid that respects slab geometry, dowel locations, and drainage. On approaches, sequence from weak toward strong support so that foam knits voids instead of trapping them. Typical spacing runs 3–5 ft, tightened where spans are larger or voids are discrete.
•  Condition & Control: Condition components so reactivity stays consistent. Ambient and slab temperatures drive in-place viscosity and rise; keep them inside the processing window, and adjust temperature and pressure accordingly. Manage back pressure so the foam travels laterally to fill before significant lift.
•  Inject in lifts: Lift in small, repeatable increments—think 2-4 in. per pass—verifying with a leveling device. This prevents over-lifting, promotes uniform load bearing, and protects doweled joints.
•  Verify & Document: Confirm load transfer by checking for panel rocking and tapping near joints under a small live load when PHOTO PROVIDED BY CRC AUSTIN, TX possible. Patch ports to location style. Log elevations before/after, lot numbers, injection volumes, temperatures, and notable observations for closeout and repeatability.

GEOTECHNICAL FOAM SELECTION

Precision lifting & load transfer: For approaches, runways/taxiways, warehouse aisles, and joint matching where tolerances are tight, choose a mid density lifting system with a predictable rise profile and robust compressive performance at installed density. For example, TerraThane 24-003 targets slab lifting across transportation and industrial bridge approaches, streets/highways, airport slabs, joint matching, and void filling. The profile suits incremental, controlled lifts where alignment and bearing are critical

Large voids & long flow paths :For undermined approaches, trench breakers, or abandonment scenarios, the priorities are long travel before setting and a manageable exotherm in mass. A formulation such as Strata-Fill 24-039 emphasizes large void filling and abandonment, with slow-reacting, low-exotherm behavior that enhances reach and let’s separate cavities knit before cure.

These are illustrative examples rather than prescriptions. Any equivalent system that matches density, expansion, closed-cell content, and hydro insensitivity for the site conditions is appropriate.

Quality and safety practices that separate pros from the pack:

•  Thermal management: Respect lift thickness guidance to control exotherm, especially in deep fills or large cavities. Excess heat compromises dimensional stability and worksite safety.
•  In-process cues: Log cream/gel timing early and re-check as ambient shifts. It is your first read on flow distance and lift onset.
•  Moisture pathways: Closed cell, hydro-insensitive foams help preserve properties in wet environments, but water still finds a way.
•  Density confirmation. For certain jobs, core samples are taken per protocol and verified for density (ASTM D1622). Where specified, compressive checks (ASTM D1621) anchor the record.
•  Crew alignment. Keep the acceptance checklist visible: target elevations, tolerance, reopen criteria, and required documentation. It keeps execution tight and stakeholders confident.

WHY GEOTECHNICAL FOAM IS STANDARD PRACTICE

Three reasons: time, control, and durability. Cure is fast enough to compress outage windows. Metered injection and predictable rise enable fine-grained elevation control in live environments. Closed-cell, hydro insensitive chemistry maintains properties where water and variable soils are a given. Add the small surface footprint, and you have a repeatable method that integrates smoothly with traffic control, flight-line constraints, and warehouse operations. In other words, polyurethane lets you solve the soil problem without creating a schedule problem.

BOTTOM LINE

Concrete lifting and void filling with polyurethane foam is no longer a specialty trick. It is a disciplined, data-driven method to restore support and elevation across transportation, aviation, industrial, and municipal assets with minimal downtime. Define the objective, choose a formulation aligned to that objective and to the environmental envelope, then run a tight field process with layered lifts, real-time measurement, and documented acceptance. Do that, and you will consistently deliver panels that are back on grade, back on bearing, and back in service. When precise lift and robust load transfer are paramount, a mid-density lifting formulation is a common fit. When the challenge is long-reach, high-volume voids, a slow-reacting, low-exotherm fill brings the travel and volume efficiency those jobs demand.

"Published by Spray Foam Magazine"