Method of making and applying chemical anchoring adhesive

Details Method of making and applying chemical anchoring adhesive Method of making and applying chemical anchoring adhesive

2000-07-26

2002-07-09

Shackelford, Heather (Department: 3673)

Hydraulic and earth engineering

Earth treatment or control

Rock or earth bolt or anchor

C052S698000

Reexamination Certificate

active

06416256

ABSTRACT:

FIELD OF THE INVENTION
This invention is directed to an improved method of making and applying a chemical anchoring adhesive into a borehole. The chemical anchoring adhesive is provided in the form of a highly viscous, self-contained rope or slug having a first resin-containing part and a second curing agent-containing part joined along an interface. The slug is sized according to a formula which takes into account the average cross-sectional area of the borehole, the average area to be occupied by an anchor pin, and the penetration factor of the anchoring adhesive into the walls of the borehole. The rope is cut to yield a slug of desired size before or after insertion into a borehole.
BACKGROUND OF THE INVENTION
Chemical anchoring adhesives are known which are composed of two or more components that react together and cure when mixed. U.S. Pat. No. 5,730,557, issued to Skupian et al., discloses a mortar mixture capsule unit for chemical attachment of anchors in boreholes. The capsule houses a filler material, and a chemical binder system contained in smaller capsules within the filler material. The cartridge is inserted into a borehole, and a driving tool is used to insert an anchor. The driving tool imparts motion to the anchor, which ruptures both the housing capsule and the smaller capsules contained within it, causing the chemical binder system to interact and mix with the filler. The interaction and mixing causes reaction and curing of the binder system/filler mixture, thereby securing the anchor within the borehole. A similar adhesive is sold by Hilti AG under the trade name “HVU”.
U.S. Pat. No. 5,731,366, issued to Moench et al., discloses a chemical plugging compound based on a free-radically polymerizable resin and a free-radical initiator spatially separated therefrom. The spatial separation can be effected by encapsulating the initiator in glass, gelatin or cellulose capsules. The plugging compound is described as being self-supporting and storage stable.
These and other prior art chemical anchoring adhesives and methods have certain disadvantages. One disadvantage is that one or both components are fluid, and must be wrapped, encapsulated or otherwise enclosed in a package prior to use. Thus, it is often not easy to vary the amount of adhesive used in a borehole, or the size of the housing capsule, while at the job site. Put another way, oversized and undersized boreholes often receive the same amount of predetermined, pre-packaged adhesive as boreholes of standard size.
Another disadvantage is that fluid adhesives may flow or spill from the boreholes during use, particularly after the package is ruptured by the anchor being driven. This problem is especially acute when the borehole is upside down and vertical, but also exists when the borehole is horizontal, or at an angle between horizontal and upside down vertical. Even when the adhesive is not completely fluid, the shapes of the prior art cartridges are typically not self-retentive, i.e., the cartridges will fall from overhead boreholes.
Another disadvantage is that the two components, binder and filler, must be completely segregated prior to use, to prevent premature interaction and reaction. The encapsulation techniques used to accomplish this require some precision and expense. Also, there is no assurance that the smaller capsules used to contain the binder will remain evenly dispersed among the filler until the adhesive capsule is used. Uneven dispersion of the binder and filler can lead to uneven or inadequate adhesion of the anchor.
Cartridge adhesives are another type of prior art adhesive. Cartridge adhesives include two separate parts which are simultaneously injected into a borehole using a two-barrel caulking gun which brings the two parts together at the point of injection, whereupon they react upon entering the borehole. Disadvantages of cartridge adhesives and methods include excessive packaging waste, excessive adhesive waste due to unmixed, unused material remaining in the caulking barrels, and insufficient viscosity, which permits the material to run out of vertical overhead boreholes, and to sag in horizontal boreholes.
SUMMARY OF THE INVENTION
The present invention is directed to a method of measuring and applying a chemical anchoring adhesive to the interior of a borehole. The method includes the steps of designing a chemical anchoring adhesive in the form of an elongated rope or slug having a substantially uniform cross-sectional area along its length. The cross-sectional area of the chemical anchoring adhesive is determined by providing a borehole having a first average cross-sectional area; providing an anchor pin having a second average cross-sectional area that is smaller than the first average cross-sectional area; and determining an average penetration factor of the anchoring adhesive into the walls of the borehole. The desired cross-sectional area of the rope or slug of chemical anchoring adhesive is then determined from the following equation:
Cross-sectional area of adhesive=(First area minus second area)×Penetration factor
The penetration factor reflects the fact that some of the adhesive penetrates into the walls of a borehole, which may be formed in concrete or another porous material. For the best anchoring results, it is desired to completely fill the space between the anchor pin and wall of the borehole with anchoring adhesive. Because of the penetration factor, the amount of adhesive required to fill this space cannot simply be calculated based on the volumetric difference, or average areal difference, between the wall of the borehole and the anchor pin. Rather, the amount of adhesive needed must be increased to account for the penetration factor, after the average areal difference has been calculated.
For a particular construction application, there are often a large number of boreholes having the same first average diameter. A large number of anchor pins with the same second average diameter are inserted into the boreholes. The penetration factor is a function of the first average diameter, the second average diameter, and the type of material (e.g., the porosity of the material) in which the borehole is formed. For these applications, the penetration factor can be determined empirically by applying varying measured amounts of anchoring adhesive into test boreholes having known dimensions and volume, driving anchoring pins into the boreholes, and determining what volume of adhesive causes the interstitial space in the borehole to be filled after the anchor pin is driven. Once the volume of adhesive is determined, the penetration factor can be determined by dividing the adhesive volume needed to fill the interstitial space by the apparent volume of the interstitial space. The apparent volume of the interstitial space is equal to:
Depth of borehole×(A
1
−A
2
)
where A
1
is the average cross-sectional area of the borehole, and
A
2
is the average cross-sectional area of the anchor pin.
Once the penetration factor is known, the desired cross-sectional area of the adhesive rope or slug can be determined from the first equation presented above. As long as the borehole material type, borehole diameter (or cross-sectional area) and anchor pin diameter (or cross-sectional area) remain essentially constant, the penetration factor, and desired cross-sectional area of an adhesive slug, will remain constant for boreholes of any depth. This is particularly useful in construction applications, where boreholes often vary in depth but not diameter.
Once the adhesive rope having the desired cross-sectional area has been provided, the rope can be cut or sheared into slugs having lengths that are precisely equal to the depths of the boreholes in which they are inserted. When the anchor pin is driven, the anchor adhesive will precisely fill the interstitial space between the pin wall and the borehole wall.
With the foregoing in mind, it is a feature and advantage of the invention to provide a method for determining and applying an amount of chemical anchoring adhesi

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