The invention relates to an anchoring rod used for anchoring an article on a base by drilling a hole in the base, inserting a compounded mass including a synthetic resin and the anchoring rod into the drilled hole.
This type of anchoring rod is known and has a head at a front end inserted in the drilled hole and a threaded portion on a rear end protruding from the hole for fixing the article to the rear end of the anchored anchoring rod.
To anchor an anchoring rod using a compounded mass, first a drilled blind hole is made in the base, the diameter of the hole being somewhat larger than the outer diameter of the anchoring rod. A glass capsule that contains the compounded mass including a synthetic resin, a hardener and additives is then inserted into the drilled hole. The capsule is crushed by insertion of the anchoring rod clamped in a drilling machine and the components of the compounded mass are activated by mixing. Once the compounded mass has hardened, the anchoring rod is firmly bonded and anchored in the drilled hole. The anchoring is based essentially on the adhesive bond between the compounded mass and the wall of the drilled hole. This bond is considerably weakened, however, when a crack runs through the location of the anchor. The compounded mass becomes detached at the wall of the drilled hole because of the drilled hole enlarging as a consequence of the crack so that only negligible holding forces remain.
Therefore DE-OS 35 16 866 describes an anchoring rod for use with synthetic resin which is provided at its front end with a head that is positionable in the vicinity of an undercut in the drilled hole as the anchoring rod is anchored. A positive engagement is thereby achieved in the region of the undercut, which enables tensile forces to be tolerated, even when a crack develops. The pull-out force, however, is largely based on the positive engagement in the undercut, so that in cracked concrete there is a considerable decline in the performance of the anchor. Furthermore, this known process requires a drilled hole with an undercut, the preparation of which requires special drilling tools.
EP-A-O 352 226 describes an anchoring means for anchoring in a cylindrical drilled hole including an anchoring rod provided with an end having an expansible cone. A parting agent is applied to the head and the shank of the anchoring rod which is intended to prevent the compounded mass from adhering to the anchoring rod. When a crack in the base occurs, the mortar compound becomes detached from the anchoring rod so that the bond between the mortar mass and the wall of the drilled hole is maintained. Subsequent slipping of the head of the anchoring rod provided with the expansible cone is intended to compensate for enlargement of the internal bore of the hardened mortar plug. When the anchoring rod is stressed, however, expansion forces are generated by the expansible cone expanding in the direction of the bottom of the drilled hole, which is precisely what is to be avoided in anchorings with composite anchors. Furthermore, there is a danger that the parting layer will be rubbed off or damaged as the composite anchor is driven in so that the desirable effect of subsequent slipping does not occur.