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Efficient grouting systems and application procedures
Machinery and equipment which have precise tolerances for alignment, or require uniform support, cannot be placed directly onto finished concrete surfaces. Both the concrete surface and the machine base have irregularities which result in alignment difficulties and bearing load concentrations.
Cementitious and epoxy grouts are used to fill the void between machine bases and the foundation. These structural grouts take on the role of transferring load between the machine and the foundation.
Grouts can be used to fill the voids between a given substrate (usually concrete) and machinery baseplates, equipment baseplates, anchor bolt holes, bearing plates, prefabricated columns, rails, and tilt-up panels.
Grouts can also be injected into surface cracks, or used for waterproofing or repair work.
Grout Properties and Main Types
The performance of a grout under a machine or equipment base depends on the properties of the grout in both the plastic and hardened states. The properties of primary importance are volume change, strength, placement ability, stiffness, and durability.
Cementitious Grouts: Most cementitious grouts have properties in both the plastic and hardened states which make them acceptable for most applications. They are suitable for transfer of large static compressive loads and for transfer of many dynamic and impact loads.
Epoxy Grouts: Generally, epoxy grouts are used where special requirements such as chemical resistance, high early strength, or impact resistance are needed. When epoxy grouts are subjected to high temperatures their properties may be significantly altered.
The success of a grouting project is dependent on the design of the foundation and the baseplate, the clearances provided for the grout, and the provisions made to completely fill the void.
Machine and equipment bases: Machine bases should be designed so that grout can be placed beneath the plate without trapping water or air in unvented corners.
If grout cannot be placed from one edge and flowed to the opposite edge, air vent holes must be provided through the plate to prevent air entrapment. Also, grout holes should be located so that the grout does not have to travel too long distances.
Grout holes should be spaced so that grouting can start at one hole and continued at other holes to ensure that the grout flows under all areas of the plate.
Concrete foundation: The concrete foundation should be designed to have sufficient strength and stiffness. If severe temperature changes are expected, wide shoulders or log pours should have expansion joints and/or steel reinforcement to minimize cracking.
Anchorage Design: The design of anchor bolts may have an effect on the grout performance. For vibrating machinery or impact loading, it is important for the grout to be maintained in compression.
Clearances: Clearances provided for grout between the machinery base and the foundation is often determined by considering the minimum appropriate thickness of grout and the maximum clearance under the baseplate possible for easy application.
Preparation for Grouting
Concrete Surfaces: The concrete surface should be relatively flat without deep pockets or grooves that my hold saturation water, or hinder the flow of grout.
The surface should be roughened to provide a key for bonding. Any concrete laitance or unsound material must be removed.
The roughened and cleaned surface should then be protected from subsequent contamination.
For cementitious grouts, the concrete surface must be continuously saturated with water for several hours before grouting.
The saturation of the surface is to prevent water from being rapidly absorbed from the grout. Rapid water loss will result in shrinkage.
Epoxy grouts require the surface to be dry unless otherwise specified.
Metal surfaces: Before placing cementitious grout, metal surfaces should be cleaned of all paint, oil, grease, loose rust, or other contaminants.
For epoxy grouts, the metal surface should be sandblasted to bright metal unless otherwise specified. If grouting is to be delayed, the clean metal surface can be primed using an epoxy resin to prevent corrosion.
Anchor bolt preparation
If anchor bolts are to be grouted, anchor bolt sleeves, holes, and similar items should be cleaned of all debris, dirt, and water using an oil-free air compressor or vacuum.
Concrete in the holes should be saturated with water for several hours and the water removed just prior to grouting when using cementitious grout. For epoxy grout, all surfaces must be dry unless otherwise specified.
Any anchor bolt sleeve or hole should be grouted before pouring grout under the plate.
This is necessary to ensure that the grout maintains contact with the plate. If total placement is attempted in one pour, air and unremoved water may rise to the grout surface. This will result in grout settlement and reduce the contact areas of the plate.
Formwork design must take into account the type of grout, the consistency of the grout, the method of placement, and the distance the grout must travel. Forms should be built so that the grout can be placed as continuously and expeditiously as possible.
Formwork must always be rigid, sufficiently tight fitting, and sealed to prevent leakage. It should extend to at least 25mm above the highest grout elevation under the machine base.
Forms should be coated with compatible form oil or wax to facilitate form removal. Care should be taken to prevent contamination of the concrete surface or the underside of the machine base with form release agent.
Formwork for flowing grout: For placement where the grout will be placed from one side of the baseplate and flowed to the other side, the forms must be constructed to provide a method of developing a head on the placement side. Forms should also have sufficient clearance to permit rodding and tamping if required.
The consistency needed for grout placement depends on the clearance provided between the machine base and the foundation, the type of machine base, and the method of placement.
Water content, or grout consistency, should not exceed the recommended maximum or minimum values determined by the grout manufacturer. The consistency for epoxy grout should be that resulting from the manufacturer’s recommendations.
Placement should not be attempted with any grout if the resulting consistency is not suitable for the existing clearances and flow lengths using the method proposed.
The ambient temperature, the grout temperature at placing, and the temperature of the substrate and baseplate, all affect workability, setting time, strength, bleeding, and volumetric characteristics of a grout.
Temperatures must be adjusted to be within the ranges recommended by the grout manufacturer. For temperatures above or below those ranges, trials should be conducted, or recommendations secured from the manufacturer.
The temperature of the substrate and the baseplate may be reduced to within permissible placing range by cooling with ice or cold water. The mixing temperatures of cementitious grouts can be reduced by using cold water, ice, or dry material stored in cool conditions.
Cementitious grouts: These must be mixed using methods and equipment which will result in a grout with uniform consistency which is free of lumps. For mixing directions refer to manufacturer’s Technical Data Sheet.
Portable revolving drum concrete mixers are not recommended, as they do not always break up the lumps in a cementitious grout.
Mixing of small quantities of plastic, flowable, or fluid grout in a bucket using a propeller-type mixer and drill is acceptable, provided the drill speed is slow enough to prevent air entrapment. Hand mixing is not recommended, as it does not provide sufficient energy to disperse constituents and break up lumps.
Epoxy grouts: Epoxy grouts must be batched and mixed according to the manufacturer’s recommendations. In general, the Grout is mixed only long enough to ensure that uniform consistency and complete aggregate wetting are achieved.
The liquid components of epoxy grouts are mixed for 3 to 5 minutes using a slow speed drill. The aggregate is mixed into the pre-blended epoxy mixture, and mixed at slow speed.
When grout is to be placed from the perimeter of a machine base, the formwork must be constructed so that a pressure head can be developed in a headbox on one side of the plate. All placement should be made from one side of the plate.
Placement should begin at one end of the plate and continue at that point until the grout rises above the bottom of the plate on the opposite side of the plate.
The portable head box can then be moved along the side of the plate from one end to the other. Continuous movement of a single face of grout prevents air entrapment.
To facilitate grout compaction and flow, rodding, tamping or flexible strapping in short strokes while maintaining an adequate head of grout is recommended.
For thick placements, control of heat generation and shrinkage is critical.
When grout is to be placed through holes in the machine base, formwork should be constructed as already discussed.
Pumping should begin at the grout inlet nearest one end of the plate. Grout should be pumped into that inlet until it flows up into an adjacent inlet and flows from the entire plate perimeter adjacent to the inlet.
The pumpline should be moved to successive inlets until grouting is complete. Grout should not be pumped into more than one inlet simultaneously because air will be trapped.
When a hose is used to pump grout under a plate, the hose should be inserted under the plate to the point farthest from the point of insertion. The hose should be withdrawn as grout is pumped under the plate.
Curing and Protection
Cementitious grouts: After placement of cementitious grouts, they must be protected from excessive moisture loss and from the extremes of temperature. Moisture is retained by the process of curing.
Curing can be conducted by keeping exposed areas wet for a given time, or by application of a curing compound which may be more practical on surfaces that are difficult to cure using continual moisture techniques.
After placement of the grout, the foundation and the baseplate must be kept at a temperature within the range specified for placing the fresh grout.
The temperature must be kept within this range until the final set.
After the final set, the grout must be protected from excessive hot or cold conditions until the final strength has been achieved.
Epoxy grouts: Epoxy grout curing is generally not affected by exposure to the air, so the main consideration after placement is protection from temperature extremes.
Temperature of the foundation and the baseplates must also be considered. During hot weather, equipment and baseplates should be shaded to provide uniform curing conditions.
Article courtesy of Sika Philippines Inc.