Types of Cement Grouting
Pressure Grouting: closely related to concrete raising, and performed using the same equipment, with the addition of a nozzle extension. Commonly referred to as soil stabilization, pressure grouting is a form of permeation grouting, and is an economical means to remediate existing and potential geological and foundation support problems without causing major disruption to structures. The process consists of the direct pressure injection of a liquefied grout (usually containing microfine cement) into voids, cracks, fractures, cavities, or even between a bearing media and a structure, foundation or bearing walls. The grouting methods can take the forms of compaction, curtain, chemical, microfine cement, slurry, or any other permeation application used to install a cement grout or low-mobility material. The method requires that the media gels or solidifies within or around the treated areas: soil, pipes, cracks, fractures, conduits, or holes. The main purposes of pressure grouting are to improve support, strength, and function of a given media, element, or substance (i.e. concrete walls, pipes, blocks, gravel, cement columns, or soils).
Permeation Grouting: penetrates voids in a mass, displacing and replacing water or air between grain particles usually at low pressure to prevent fracturing. Grouts are designed and intended to “permeate the sub-grade or soil” and stiffen the mass as a whole. If a cementitious grout is used, it must be thoroughly mixed with a high-shear mixer (proper functioning volumetric mixers, as modified by Concrete Raising of America, exceed high-shear capability). Chemical grouts or microfine cement grout, alone or in combination, work well for this method.
Penetration Grouting: grouting used mainly to fill joints or fractures in rock or large pore spaces in order to strengthen the existing mass and eliminate movement or water flow, without disturbing the formation. It requires a slurry mix design of water, Portland cement, fly ash, sand, or any combination thereof.
Compaction Grouting: (as defined by the Committee on Grouting of the Geotechnical Engineering Division, ASCE’s): Grout injected with less than one inch (25mm) slump, normally a soil-cement with sufficient silt sizes to provide plasticity together with sufficient sand sizes to develop internal friction. The grout generally does not enter soil pores but remains in a homogeneous mass that gives controlled displacement to compact loose soils, gives controlled placement for lifting structures, or both. Compaction grouting requires comprehensive subsurface investigation. Generally, these types of grouting jobs will incorporate a Geotechnical Engineering Consultant, whom will likely prepare an on-site investigation report and “Grout Plan” based upon site geology, history, soil gradation, and the in situ permeability (horizontal) of each stratum for treatment. Compaction grouting jobs require a contractor to directional drill for pipe placement into loose soil stratum, placement and frequency of holes for grouting are contingent upon the engineer’s Grout Plan. Grouting takes place through the pipe, and is typically performed bottom-up, but can also be top-down. Grout consistency and grouting pressure are vital to the process which will likely require a volumetric mobile mixer (on-site batching/delivery) and a pump capable of pumping a stiff grout (generally rated at 900 p.s.i. or higher).
Compensation Grouting: also known as “Fracture Grouting” involves injecting a grout slurry and hydrofracturing the soil between the foundation to be controlled and the causation of settlement. The slurry is forced into fractures, causing expansion and raising. Multiple injection locations and multiple levels of fracture(s) create a more-permanent reinforced structure. Pipe sleeves are required for various level slurry injection. Grout consistency is again vital to the overall process.
Jet Grouting: is a ground modification methodology used to create soilcrete (in situ, cemented formations of soil), which are commonly used to provide: 1. underpinning and/or excavation support; 2. Temporary/permanent stabilization of soft or liquefiable soils; or 3. Groundwater and/or underground pollution control. Jet Grouting has three traditional systems which differ by application and desired physical characteristics of the soilcrete. Typically, grout is pumped through a rod and exits a horizontal nozzle(s) at high velocity [approximately 650 ft/sec (200m/sec)]. This energy breaks down the soil matrix and replaces it with a mixture of grout slurry and in situ soil (soilcrete).
Chemical Grouting: within the industry, there are two (2) classifications of chemical grouting: structural and water control. Structural-the permeation of sands with fluid grouts to produce load-bearing sandstone-like masses. Water Control-the permeation of sands with fluid grouts to completely fill voids to control water flow. Typical chemical grouting agents include: Sodium Silicates, Acrylates, Acrylamides, Polyurethanes, and MC-Silicates. Seemingly the most common agents remain sodium silicate (an acrylamide generally used with a hardening agent) and polyurethanes, of which there are two (2) types: hydrophilic and hydrophobic. Hydrophilic chemical materials incorporate large amounts of water in their structure, which creates a gel. This type of material can shrink if allowed to dry. Therefore, it is vulnerable to breakdown. Hydrophobic materials use water as a reacting agent, so soil moisture content and free standing water in voids are of major concern. The cured material is essentially water free, which makes it resistant to shrinkage. This type of grouting material remains flexible and is used in moving cracks.