In most typical concrete slab installations, the slab has a tendency to settle after a period of time, moisture or water being the cause most often associated with the settlement. Poor soil conditions following a close second. A commercial airport does not fit the typical installation procedures. Far more preparation of the subsurface soils, higher compression concrete, thicker slabs and higher standards for quality control, are followed yet all commercial airport slabs are susceptible to the same settlement and/or slab rocking found in any other commercial, municipal or residential installation. Heavy traffic and weather caused erosion will eventually cause subsurface voids, poor soil compaction, water intrusion, (causing subsurface water pockets and erosion of the fines in the subsurface and deeper layers), and finally settling sedimentary layers deep below the surface. The end result? Concrete settlement and/or slab rocking, eventually cracking and slab failure.
Traditional methods of repair including removal, compaction, and replacement, and/or heavy mud/concrete pressure grouting have proven to effective but costly and very time consuming. Down times can often be measured in weeks, sometimes months.
Using Polyurethane as the Viable Alternative
Deep injection of single or plural component polyurethane soil stabilizers combined with the injection under the affected slabs of plural component polyurethane concrete lifting foam to stabilize and lift the slab can reduce the down time from days and weeks to just hours. In applications other than runway or apron traffic, the down time is measured in minutes. Slab rocking occurs in almost all heavy vehicle traffic locations. [Rocking slabs constructed on unbound sub-bases can cause ‘steps’ at joints, the main cause being movement of the sub-base. As heavy vehicles travels over a joint, the slab on the approach side is deflected downward. When the wheel leaves, it quickly deflects upwards creating a gap of low pressure between the slab and the sub-base drawing material from beneath the departure slab to the other side of the joint. After many passages from the vehicles, a significant amount of material is moved across the joint, resulting in ‘stepping’, ultimately leading to slab cracking and slab rocking].
High moisture content can and will cause settling of sedimentary layers beneath the slab and/or create water pockets that may eventually cause failures in the slab itself. Injecting polyurethane formulated specifically for high moisture area can displace water altogether and due to the closed cell characteristics act as a barrier for future water intrusion.
For more information: Airport Runway Lifting