Foam jacking is a fast, economical repair process for correcting settled and unstable concrete. From sidewalks to interstates, and everything in between, foam jacking is economical, fast and effective for economically correcting settlement and instability.
How foam jacking works
Two polyurethane liquid components are mixed and injected (hence also being called polyurethane injection) under pressure below the area or structure being repaired. The two liquids react with each other, expand and harden, like the foam you get in a can to seal around windows. Our polyurethane foams stay a liquid for a few seconds before expanding to help them spread out from the exact spot they’re injected, but then get harder much faster, and can exert much more force during expansion. The foams we use, (TerraThane), are specially formulated to be very strong and perform well in contact with the ground.
Advantages of foam jacking
There are lots of advantages to foam jacking as compared to other methods of repair, such as slab jacking, grinding and replacement. Foam jacking has primarily been used in the infrastructure and industrial markets; for many jobs, such as lifting and stabilizing interior floors, foam jacking is almost unquestionably the best repair process available. Foam jacking is…
Foam jacking is the cleanest concrete lifting and stabilization process. Because the injection equipment is mechanically connected to the slab or structure, and mechanical seals engage when not injecting material, no loose material is introduced to the repair area. Dustless drilling is easily accomplished, and even non-dustless drilling is essentially mess-free due to the small hole size. There is no grout or mud to track around job sites.
Foam jacking is the quietest and fastest process for stabilizing and raising settled concrete slabs. Because of the small hole size, drilling is fast and quiet, and there is virtually no noise associated with the injection process itself. The equipment for foam jacking is self-contained in a box truck, which is typically parked away from the direct work location.
Foot traffic during work is functionally OK, and immediate resumption of vehicular traffic after work is completed can be expected. Foam jacking is not affected by foot traffic during the injection process; as long as pedestrians are able to step over or around the injection equipment, they may continue to use the area being repaired. Vehicular traffic may resume immediately after work is completed. This includes heavy loading such as trucks and industrial equipment like fork lifts, and even trains.
Foam jacking crews can lift up to 12 times faster than standard slab jacking or mud jacking crews in many situations. Because of the small hole size and ability to lift larger areas per hole, foam jacking is much quicker than slab jacking. Because of the equipment design, upon arriving on a job, foam jacking crews are typically actively lifting slabs within 10 minutes of arrival for typical repairs.
Light weight material reduces the overburden on underlying soils, reducing the chances for resettlement. Even the highest density polyurethane foams used for foam jacking are significantly lighter than alternative lifting and stabilization materials. This reduces the amount of additional burden weight placed on the underlying soils.
High density polyurethane is waterproof, so treated slabs are thoroughly undersealed. Polyurethane can also be installed in water, so flow testing or water stop applications with active flows are not a problem. Because of the near-immediate curing, water stopping jobs are fast and easily tested on site to ensure efficacy of the repairs.
What foam jacking is best for
There are many times when foam jacking is the only repair process that will address a problem. Here are some of the times when foam jacking is best:
Large slabs (typically bigger than 100 square feet) are best repaired with foam jacking because polyurethane can travel under the entire slab from just one or two injection holes, creating a more diffuse lifting force than grout. This speeds up work and lessens the chance of cracking. Faster reacting lower density foams typically start to expand within a few seconds of injection, so they are good for concentrated lifting. Slower reacting, higher density foams can travel as a liquid for up to 45 seconds before starting to expand and harden. This allows them to lift extremely large areas, as the liquid is injected at 600 psi, which forces it into what can be very small spaces under the slab.
Because of its high expansion force and ability to spread under large areas of slabs and structures before expanding, high density polyurethane can lift extremely heavy slabs with ease. These include roadway slabs, bridge approaches, rail crossings and slabs with heavy loads, such as machinery bases and floors with backup battery power packs.
Areas where cleanliness is important
Due to the small, infrequent holes, dustless drilling is easy. Additionally, because there is a mechanical connection between the injection equipment and the slab, not material is exposed to the surface or surroundings. Automatic, mechanical valves on the injection equipment prevent leakage of material when not injecting.
Sensitive or expensive surfaces
Because foam jacking uses small (dime-size) holes that can be placed infrequently, it is an ideal repair method for settled slabs which have decorative coatings, surface treatments or other characteristics, such as brick and stone overlays. Injection holes can be patched with stained concrete to blend in with floor coverings. For repairing slab floors with wood, we use a 1″ hole saw to cut a small access area to the floor, which can then be puttied back into place after lifting is completed. For carpeted areas, three sides of 2″ squares can be cut to reveal floor and then be glued back down after injection.
Load sensitive areas
The most common cause of slab settlement is inadequate compaction or bearing capacity of the underlying soils. Because high density polyurethane is lightweight (typically 2.5 to 6 pounds per cubic foot), there is very little additional weight transferred to the underlying soil as part of repairs. This helps to minimize the chances of resettlement. Sand-based and cementitious grouts used for slab jacking or pressure grouting typically weigh more than 100 pounds per cubic foot, so the weight savings with foam jacking are significant.
Because high density polyurethane is stored and transported as a liquid which then expands, a single non-CDL box truck can easily transport more than 80 cubic yards of expanded material. The equivalent for slab jacking grout would require more than 6 large dump truck loads and onsite handling equipment. Raw polyurethane material is transported in standard chemical totes, so is easily transported, stored and handled on job sites.
Other names for foam jacking
Foam jacking, particularly for residential applications, is in its infancy in our market (Mid-Atlantic). Foam jacking is referred to as polyurethane concrete raising, poly jacking, poly leveling and other similar names in other areas.
Materials used for foam jacking
Concrete Jack installs the TerraThane line of polyurethanes from NCFI. The chart below shows some basic characteristics of some foams Concrete Jack installs.