by Norman Aceron Garcia
Concrete collapses when the underlying sub-base aggregates scour due to insufficient compaction or natural erosion. Sunken concrete can result in various structural defects such as bowed basement walls, cracked foundations, uneven concrete pads, recessed sidewalks, un-level concrete junctions, foundation settling and failed retaining walls. If these minor defects are not remedied, it can escalate to major structural problems and water runoff. Aside from being an aesthetic issue, uneven surfaces pose major trip hazards to pedestrians, thereby decreasing the functionality of sidewalks and driveways.
The common solution for uneven foundations or sinking driveways and sidewalks is to demolish the old concrete slab and pour a new one. However, this process is costly and takes a considerable amount of time and inconvenience. Nowadays, we use an alternative solution that is less intensive, called mud jacking, also known as slab jacking, pressure grouting, or concrete levelling. Mud jacking is the process of injecting concrete slurry beneath the sunken concrete slab in order to raise it back into its original elevation.
The installer drills small holes into the concrete, then slurry, composed of different materials, such as cement, sand, soil, limestone, bentonite clay, water or expanding polymers, is pumped into it. The appropriate slurry depends on the type of application and the installer’s preference. The injected slurry fills any voids and forces the concrete to rise back into place. The drilled holes are then patched up with hydraulic cement. After a curing period of 1-2 days, the slurry strengthens and amalgamates the underlying soil, which prevents the slab from sinking further. Although mud jacking is not a complicated process, it must be done only by trained tradespeople because amateur or sloppy workmanship can lead to more damage. The location of the underground utility lines such as electrical lines, drain pipes, and sewers must be identified first to evaluate if such lines can withstand the mudjacking process.
Advantages of mud jacking over the traditional way of demolishing and re-pouring concrete include:
- Environmentally friendly – mud jacking rehabilitates the existing concrete that could have ended up in the landfill;
- Fast installation – mud jacking may only take hours, whereas concrete pouring could take days depending on the curing time;
- Inexpensive – because there is no demolition involved, the price of mud jacking is approximately half as much as concrete replacement; and
- Efficiency – mud jacking requires less labour, equipment, and disturbance to the surrounding area.
However, mud jacking has some limitations in situations such as:
- The presence of a sinkhole or swampy soil underneath the pavement;
- When the concrete surface is spalling or the remaining concrete has completely collapsed. The mud jacking process could further damage the concrete surface even after it is elevated back into place;
- The concrete has swollen up due to expansive soil, in which the only solution for this is to demolish and re-pour the cement.
Norman Aceron Garcia is a Professional Engineer of Mr. Peg Property Inspections Inc. Please e-mail firstname.lastname@example.org for free technical consultation.