Typical Equipment and Materials Used for Slabjacking

Equipment

Basic equipment on a slabjacking job includes a rock drill, grout mixer, and grout pump.

Make sure to keep all equipment in good working order and regularly maintained. Equipment failure during the slabjacking operation can result in project complications.

Grout mixers are often the weak link in the operation, causing a great deal of maintenance problems and downtime. They are most often high-speed colloidal shear mixers or the equivalent, being capable of producing a consistent and homogeneous mixture free of lumps. Smaller jobs may require only a mortar mixer to adequately mix the grout. The mixer should have at least a 7-cubic foot capacity with about 10 horsepower engines, and be built to withstand heavy use. The consistency of the grout has to permit a consistent flow of material under the slab to ensure spread of the grout and even lift.

Other features may include:

  • Providing maximum air circulation with an engine housing designed for maximum air circulation by providing additional vent holes. This prevents heat build-up.
  • Beefing up the suspension and rebuilding the tow bar.
  • Using an enclosed gear drive as opposed to belts for fewer breakdowns.
  • Wheel bearings last longer if there are hub caps on the wheels to keep dust and debris out.
  • Using all steel mixer blades rubber tipped blades wear out more quickly.
  • Making sure there are handles on the trailer tongue to reduce the chances of worker foot injuries while the mixer is being maneuvered.

Grout Pumps are typically either positive displacement hydraulic piston pumps; air-operated, double diaphragm pumps; or hydraulically operated progressive cavity pumps. The output of single-cylinder hydraulic piston pumps is up to 110 cubic feet per hour, and a 180 cubic feet per hour output from dual-cylinder models. Which ever pump is chosen for the job, it should be capable of delivering variable pressures from 1 to 100PSI, and be able to deliver the grout in a uniform and consistent manner. The pump should also be able to deliver a minimum 60 GPM. The pump control is placed at the injection nozzle.

Slabjacking units are available that are a combination of a paddle-type mixer and a piston pump. However, these higher-end, high-output units are usually most suitable for high production jobs, such as highway construction, where they can pump several cubic yards of grout per hour at line pressures up to 600 psi.

A Rock drill or Coring machine that prevents excessive dust and breakout at the bottom of the slab is typically needed. The drill bit should have four points, and maintained to ensure that the holes are not " out-of-round". A gas-powered rotary percussion drill with a 2- or 2 -inch diameter bit is a common tool for this application.

Materials

The Grout used in slabjacking is a mixture of water, Portland cement, and some combination of limestone dust, fly ash or sand as well as additives. The consistency has to be of a homogeneous paste with sufficient slump to ensure that all voids are filled to prevent undue stress on the slab. The comprehensive strength needs to be 5 Mpa minimum.

Type 10 Normal Portland Cement is used unless otherwise specified. Type 20 Moderate Portland Cement is used where precaution against moderate sulphate attack is important. Type 40 Low-Heath of hydration Portland cement is used where rate and amount of heath must be minimized. Type 50 Sulphate-Resistant Portland Cement is to be used where grout is exposed to severe sulphate action.

Cement content may range from 5% to 20% by weight of dry materials, depending on the setting time required.

Sand: Fine sand (5mm) with no silt permitted is used

Additives: Bentonite is used to promote lubrication which ensures complete void filling and to reduce bleed. The proportions should not exceed 12% to avoid compromising the strength.

Expanders are used to compensate for shrinkage during curing.

Cement fondue is added to promote rapid set if required.

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