Unisorb - Grouting Products - UNISORB - #9

By WAYNE H. WHITTAKER, V.P./G.M., Unisorb Installation Technologies, Jackson, MI

The grouting of machine base plates and bearing plates, and of an­choring/alignment equipment to a foun­dation are low-cost approaches that provide a high quality machine-to-foun­dation connection. A successful instal­lation depends on: proper grout selec­tion, based on application; foundation preparation; forming method employed; and careful attention to the actual appli­cation of the grouting material.

Grout Selection—Selecting grout for a particular application should in­clude an evaluation of these factors:

1. Cost—Compare the cost of mixed grout, ready for placement. Yields can vary considerably from one manufacturer to another, and dry powder to price comparisons are misleading, as the amount of mixing water required will also vary.

2. Strengths—Applied loads should be evaluated carefully to ensure that the bearing capacity of the grout is not exceeded. Compressive strengths reported by manufactur­ers are based on tests run under lab conditions; actual field-cured val­ues for cementitious grouts will be approximately 80 percent of the lab result.

3. Ease of handling and place­ment— The following factors are important:

A. Flowability. The ease with which the material enters small cavities and travels under larger base plates is usually measured either by the ASTM-C230 test or Corps of Engineers Spec CRD-621flow cone test. For the ASTM-C230 test, the results are expressed as a dimensionless number ranging from 100 to 150, with 150 the most flowable. The Corps of Engineers' results range from 30 seconds to 10 seconds, with 10 seconds the most flowable.

B. Tendency to separate when mixed or handled excessively. In some materials that use me­tallic additives or have aggre­gates of widely varying sizes, the aggregates tend to separate if the material is overmixed or handled excessively.

C. Ability to be pumped or vi­brated, particularly on larger in­stallations. Again, separation is the problem. The ability to be vibrated or pumped is a prime

concern when grouting cavities are small, when placement is difficult, or when grout must be flowed long distances.

D. Expansion or nonshrink prop­erties. The main objective is to select a material that will expand enough to assure full bearing contact with machine base and foundation (a few tenths to 1 percent or so is normal). When large grout-to-machine contact areas are encountered, a grout with a controlled internal pres­sure development should be selected to prevent the grout's expansion from disturbing align­ment. The actual expansion of a grout is typically measured by either the ASTM C-1090-88 or ASTM-C827-87 early volume change method; the result is expressed as a percentage.

E. Maintenance requirements.

What will be required to keep the grout functional in the environ­ment into which it will be placed is the main concern. For ex­ample, a grout that is to be used in an oily environment should be a relatively impermeable type. A grout with a porous structure will require a paint coat to prevent penetration by oils and other chemicals.

Other special considerations include ability to withstand thermal cycling and high temperatures, ability to resist ac­ids, and susceptibility to spaulding un­der freeze-thaw cycling.

Materials in use today range from slightly modified sand and cement mix­tures to chemically sophisticated ep-oxy materials with strengths five to six times that of standard concretes.

Cementitious Grouting Materi­als—The simplest grouting material consists of sand and cement mixed at approximately a 50-50 ratio. Simple sand and cement mixtures shrink on curing, usually from 2 to 3 percent, making their use in high load or preci­sion applications questionable. Cementitious grouts in use today have

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1. Foundation forming and finishing tolerances may be relaxed. Because grout provides the final link between the machine and the foun­dation, the foundation is usually finished 1V2 to 3 in. below the desired machine base level. A thicker or thinner grout pad can be used, as the specific situation requires, to compen­sate for the variances encountered in actual foundation construction, eliminating the need for precision foundation work.

2. Grouting provides a rigid machine-to-foun­dation connection. As the grout is placed into the cavity, in the plastic or fluid state, it conforms precisely to the machine base and to the foundation, providing a 100 percent bearing contact between foundation and grout pad, and grout pad and machine base.

3. Anchoring/alignment equipment can be positioned within a precast or core-drilled grouting cavity at the time of machine installation. As the foundation is constructed, grouting cavities are created by precasting or core drilling (while the foundation is green) at the approximate location of each support or anchor point.

When the foundation has cured sufficiently to support machine loads, the machine is moved into position on the foundation and sup­ported by temporary blocks. The anchoring/ alignment equipment is then assembled to the machine base with the anchor bolt and base of the alignment device (if one is being used) projecting into the grouting cavity. Grout is then placed into the cavity and allowed to cure, completing the machine-to-foundation connection. This approach eliminates the requirement for time-consuming, precise pre­setting of anchor bolts or alignment equip­ment, significantly lowering the cost of more complex installations.

4. Existing foundations may be easily adapted to new equipment. Core drilling an existing foundation to accept new anchoring/align­ment equipment, which is in turn grouted into permanent position, eliminates the need for removing and replacing an otherwise sound foundation if the equipment it supports is being relocated or replaced. When properly installed, these anchors exhibit holding power equal to or better than that of anchors set into the foundation as it was constructed.

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