Void Filling With Polyurethane in the Chicagoland Area
Using polyurethane for void filling consists of injecting high density polyurethane foam under the concrete where voids are detectable.
Material
The material used in void filling is a high-density water-blown polyurethane. The material is hydrophobic and has the following physical characteristics and properties:

Free Rise Core
Density (lb/Ft.3) Compressive Strength (psi @ yield point)
ASTM1622 ASTM 1621
3.8-4.2 60-69 PSI

The polyurethane foam system has free rise density of 3.8-4.2 lb/ft3, with a minimum compressive strength of 69 PSI. The expansion of the polyurethane foam under pressure increases the foam density above the original free rise density value. Compressive strength is a function of density of the tested material. As some packing of material will occur to ensure fill, the final in-place density will be slightly higher than the free-rise density
Equipment

Pumps: A truck mounted or other pumping unit capable of injecting high density polyurethane, at a controlled rate, into the void directly beneath the concrete pavement. The pumping unit is equipped with a meter to measure the amount of high density polyurethane injected at each location and capable of instantaneous control of the material flow to avoid lifting of the pavement slabs.
Drill: The equipment shall be in good condition and operated in such a manner that the holes are vertical and sufficiently round to permit sealing by the injection port. Drills for grout injection are pneumatic or hydraulic rotary percussin types.

The Process

Drilling Holes: Holes are between 5/8” ± 1/8”. Hole drilling patterns for concrete void filling are determined on-site and based on conditions such as the size or length of the concrete area to be stabilized, the elevation difference, subgrade and local circumstances. The hole pattern is a grid on approximately 7-foot centers. Each hole pattern is modified on-site in case adjustment to site conditions is needed.
Pumping Polyurethane: During stabilization operations, the upward movement of the slab is closely monitored. The amount of rise is controlled by regulating the rate of injection and quantity of material.
Curing Time: Within only 15 minutes, the high-density polyurethane formation will reach 90% of full compressive strength.
Patching Holes: Upon completion of pumping, any excess material is removed from the pumping site. Drill holes are then filled to the concretes surface using a non-shrink sand cement. Mortar for filling the holes in the concrete slab are generally composed of one part Portland cement and two parts fine aggregate, and enough water to allow for the placement and packing of mortar into the holes.