Composite anchors are indispensable in construction, concrete demolition and special demolition as well as in rock breakout and tunnel construction. They provide positive mechanical load transfer fastening in concrete, masonry, and rock and are also used for post-installed rebar connection. In practice, specialists at Darda GmbH encounter composite anchors in many project steps: when securing components prior to using concrete demolition shear, when temporarily suspending elements before cutting, and when stabilizing rock structures in natural stone extraction. This article classifies the term technically, explains execution, and highlights touchpoints with equipment such as rock and concrete splitters in professional settings.
Definition: What is meant by composite anchor
A composite anchor is a fastening system in which an anchor rod, a threaded rod, or a post-installed reinforcing bar is fixed in a drilled hole by means of reactive resins or mineral mortars. Load transfer occurs via the bond interface between the injection mortar (or capsule resin), the anchoring element, and the base material (non-prestressed or prestressed concrete, masonry, rock). Unlike mechanical expansion anchors, the holding force does not arise primarily from expansion, but from a chemical-adhesive and mechanical interlocking along the borehole wall.
Structure and operating principle of composite anchors
Composite anchors typically consist of the base material (concrete, natural stone, rock, or masonry), a drilled hole of defined geometry, the bonding agent (e.g., vinyl ester, epoxy, or hybrid mortar), and a metallic insert (threaded rod, internally threaded anchor, reinforcing bar). Observing edge distance and spacing, the cured mortar forms a force-transmitting zone that introduces tension, shear, and combined loads into the component or rock mass.
Types, materials, and chemical systems
Composite anchors are differentiated by installation method, resin system, and anchor element. Selection depends on substrate, load level, temperature, moisture, and installation conditions (e.g., overhead, water-filled holes).
- Injection systems: two-component mortars in cartridges; mortar and hardener are mixed during dispensing and introduced into the hole via a static mixer nozzle.
- Capsule systems (cartridges): glass or foil capsules with resin and hardener; components are mixed during the anchor’s setting/rotation.
- Post-installed rebar: reinforcing bars are bonded at a defined embedment depth to create load-bearing rebar connection.
- Mortar types: epoxies (high performance, longer cure), vinyl ester/hybrid (faster cure, practical), mineral mortars (e.g., cementitious for greater hole depths in rock).
Planning and design in construction and deconstruction contexts
The design of composite anchors considers resistances, edge distance, embedment depths, concrete compressive strength, crack condition, temperature ranges, and, where applicable, fatigue. In deconstruction, temporary load cases are especially relevant, such as propping components before using concrete demolition shear or setting anchorage points for lifting gear during building gutting and concrete cutting. In rocky environments, composite anchors are used as rock bolt for short-term stabilization before stone splitter and concrete splitter perform controlled separations. Design and approval conditions must be checked project-specifically; requirements from recognized rules of the art must be observed.
Drilling, borehole cleaning, and installation sequence
Installation quality is crucial for load-bearing capacity. Especially in dust-intensive environments of concrete demolition or natural stone extraction, a clean borehole surface is essential.
- Drilling: Create the hole using a suitable method (hammer drilling, core drilling, if necessary compressed air in rock). Geometry per system specifications (diameter, depth, tolerances).
- Cleaning: Multi-step blow-out and brushing until pores are visibly clean. In damp or water-filled holes, use specified cleaning and mortar systems.
- Injection: Attach cartridge, purge the mixer until the mixture is homogeneous; fill the hole from the bottom up (inject while withdrawing to avoid air inclusions).
- Insertion: Press and rotate the anchor rod to the required depth; remove excess mortar, fix installation position.
- Curing: Observe waiting times per temperature; only then tighten or load.
- Documentation: Record batches, temperatures, curing times, visual checks, and where applicable the anchor pull-out test.
Composite anchors in concrete demolition and special demolition
In selective deconstruction, composite anchors frequently secure temporary brackets, guide rails, anchorage points, or protective structures before load-bearing elements are released with concrete demolition shear or Multi Cutters. On existing installations, composite anchors are identified and unloaded during dismantling, for example before steel shear separates attachments. For controlled work steps, load paths must be clearly planned: where composite anchors are holding components, these are unloaded before mechanical separation to prevent uncontrolled movement.
Coordination with concrete demolition shear
During nibbler-style removal of concrete members, existing composite anchors can influence material removal. Anchor steels embedded in bonded mortar are tougher to release under shear than pure expansion anchors. In practice, the bonded zone is exposed (e.g., by careful nibbler removal), the anchor is released or cut flush, and the remaining bond area is repaired later.
Interaction with stone splitter and concrete splitter
In massive members or block rock, it may be necessary to implement safety measures prior to controlled splitting. Temporary composite anchors can then stabilize edge areas, hold covers, or attach monitoring points. After the splitting operation, these temporary fixings are typically removed or overdrilled.
Applications in rock breakout and tunnel construction
In rock engineering, composite anchors are used as rock bolt (fully bonded) to secure rock slabs, stabilize work areas, or take loads from support elements. Fast-curing capsule resins enable short waiting times during advance; in water-bearing zones, suitable mortars and cleaning procedures are used. For subsequent separation with stone splitter and concrete splitter, systematic anchor planning helps prevent unintended crack propagation and allows blocks to be released in a controlled way. This aligns with practices in rock demolition and tunnel construction.
Building gutting and concrete cutting: Temporary fixings
During building gutting and concrete cutting, machine guides, dust extraction hoods, scaffolds, or safety ropes are often fastened with composite anchors. Prerequisites are suitable base materials and observing edge distance so that no cone failures occur during cutting, sawing, or milling. After completion, the surface is evened, for example by overdrilling and reprofiling.
Removal, overdrilling, and repair
The removal of composite anchors is performed as required by unscrewing, cutting flush, overdrilling with a larger diameter, or core drilling. After cleaning, the remaining cavity is closed with appropriate repair mortars. In areas later processed with concrete demolition shear, exposing and pre-cutting anchor rods has proven effective to avoid uncontrolled cracks.
- Flush cutting: remove the head, fill the recess, and level.
- Overdrilling: create a larger hole, remove bond and anchor, then reprofile.
- Core drilling: locally remove where reinforcement density is higher or diameters are large.
Quality assurance, testing, and documentation
For load-bearing applications, random anchor pull-out test and visual inspections are common measures. Documentation includes base material classification, drilling and cleaning steps, mortar batches, temperatures, curing times, and installation torques. For temporary anchorage points in special demolition, an increased test frequency can be sensible, especially with changing substrates or weather conditions.
Occupational safety and environmental protection
Drilling generates fine quartz dust; suitable dust extraction, wet drilling, and personal protective equipment are standard. Resin systems can contain sensitizing components. Skin and eye protection, careful handling, and adherence to manufacturer information are standard practice. Extruded resin residues, mixing nozzles, and contaminated material are collected separately and disposed of properly. In enclosed spaces, ventilation concepts are helpful, especially for extensive injection work.
Typical failure modes and how to avoid them
- Insufficient borehole cleaning: reduced bond, lower capacity. Countermeasure: documented brush–blow-out–brush–blow-out sequence.
- Wrong mortar for damp/wet holes: bubble formation, poor adhesion. Countermeasure: use systems for wet substrates.
- Incorrect embedment depth or edge distance: cone breakout or spalling. Countermeasure: drilling templates, markings, consistent dimensional control.
- Loading before curing: creep behavior, settlements. Countermeasure: observe temperature-dependent waiting times.
- Over-torque/excessive tightening: bond damage. Countermeasure: torque-controlled tightening, follow specifications.
Terminology and placement in practice
Composite anchors differ from mechanical anchors (expansion anchors, undercut systems) through the bonded holding principle. Compared to anchors such as heavy-duty anchor, they offer advantages with small edge distance, in cracked concrete, or for post-installed rebar connection. In Darda GmbH practice, composite anchors are often considered as temporary auxiliary constructions before tools such as concrete demolition shear, attachment shear, or tank cutter are used. In rock breakout and tunnel construction as well as natural stone extraction, bonded rock bolt support the safe sequence of drilling, splitting, and lifting processes, for example when working with stone splitter and concrete splitter or rock wedge splitter. Thus, the composite anchor, whether permanent or temporary, integrates seamlessly into planning, securing, and separation workflows.