Anchors – often also called concrete screws, screw dowels, or concrete screw anchors – are mechanical anchoring elements for fast, secure, and often repeatedly removable fixation in concrete and, with limitations, in dense natural stone. In the context of Darda GmbH they are typically used wherever temporary or permanent anchorage points are needed during concrete demolition and deconstruction, building gutting and concrete cutting, in rock demolition and tunnel construction, as well as in natural stone extraction. This includes auxiliary structures and anchorage points for positioning concrete demolition shears or for brackets and shoring when working with hydraulic splitters.
Definition: What is meant by anchor
An anchor is an anchoring element screwed into a predrilled hole whose special thread cuts load-bearing thread grooves into the base material during installation. Loads are transferred by positive mechanical interlock directly into the concrete or dense stone. Anchors are usually made of steel (zinc-plated) or stainless steel, are available with various head shapes (hex head, countersunk head, internal thread), and cover tension and shear loads. Characteristic features are rapid installation, the option of removal by unscrewing, and, compared to bonded systems, the minimal curing time – in fact, none is required.
Design and operating principle of anchors
The load-bearing behavior is based on a cutting, partly saw-tooth-like thread that, when screwed into the predrilled hole, creates a form-fit engagement in the concrete. The screw-in depth and the drill diameter are central to this: they define the effective thread length and thus the load transfer. Depending on edge distance, member thickness, and concrete strength, the limit states of concrete failure (cone pull-out, edge spalling) and steel failure are designed. In cracked concrete, suitable anchors are used that are rated for crack widths within the approval. Under dynamic actions – for example, vibration excitation from demolition tools – adequate preload and controlled tightening torque are important to minimize embedment relaxation.
Types of anchors and suitable substrates
Anchors differ by head shape, material, thread geometry, and approval scope. In practice, three aspects are decisive: base material, corrosion exposure, and installation access. In Darda GmbH applications, concrete substrates dominate; for natural stone, a case-by-case assessment is required.
Concrete and reinforced concrete
In uncracked and cracked concrete (e.g., C20/25 to C50/60), concrete screws are widely used. They are installed in pre-positioned installation and allow short edge distances and small center-to-center spacing – within the respective approval. For temporary auxiliary structures, such as brackets for positioning concrete demolition shears or anchorage points when working with hydraulic splitters, a removable fastening is often preferred. This is where the anchor plays to its strengths: quick to install, retightenable if needed, and removable with minimal residue.
Rock and natural stone
In dense natural stone (e.g., granite, basalt), anchors can perform well provided the stone is sufficiently homogeneous and strong. However, variability in material properties is greater than in concrete. Prior to use – for example in rock excavation and tunnel construction or natural stone extraction – field tests and anchor pull-out tests are advisable. In bedded or weathered rock, special caution is required. Alternative anchoring systems are evaluated for critical locations.
Planning and design for use in deconstruction and extraction
The selection of an anchor depends on load level, load type (tension, shear, combined), substrate, boundary conditions (edge distances, member thickness), environmental influences, and installation conditions. In the Darda GmbH fields of work – whether concrete demolition and special demolition or building gutting and concrete cutting – additional temporary load cases and changing situations must be considered.
- Drill diameter and drill-hole depth matched to the anchor
- Screw-in depth coordinated with tension and shear loads
- Edge and center-to-center distances according to design
- Concrete condition: cracked/uncracked, moisture, temperature
- Corrosion protection: zinc-plated or stainless according to environment
- Required tightening torque and verification
- Planned removal and surface reinstatement
Load transfer on temporary brackets and guide fixtures
When working with concrete demolition shears or using hydraulic splitters, auxiliary brackets, guide fixtures, or stops are often fastened. Acting loads include:
- Shear loads from the self-weight of the auxiliary structure and tool guidance
- Tensile loads from preload and installation
- Additional dynamic components due to vibrations
The design considers the governing combination. Adequate member thickness minimizes the risk of edge spalling. Large washers can distribute bearing pressure but do not replace structural verification.
Installation: step by step
- Lay out and mark drilling points, observing edge and center-to-center distances.
- Drill using the specified drill diameter and depth stop. Reinforcement is bypassed where possible; if encountered, adjust the position.
- Clean the drill hole: blow out, brush out, blow out again. Residual dust reduces capacity.
- Screw in the anchor to the required screw-in depth. The head should bear flush.
- Tighten to the specified tightening torque, preferably with a torque wrench.
- Install the attached component (bracket, holder, rail) and check bearing contact.
- Document installation parameters and perform sample anchor pull-out tests at critical points.
Tools and quality assurance
For reproducible installation you need: rotary hammer with suitable bit, depth stop, blower or hand pump for hole cleaning, torque wrench, gauges for depth and edge distance, and, if required, a portable test system for pull-out tests. In Darda GmbH practice this is often aligned with workflows around hydraulic equipment when fastening auxiliary structures for concrete demolition shears or positioning hydraulic splitters.
Special requirements in concrete demolition and special demolition
Deconstruction projects are characterized by changing substrates, moisture, dust, and vibrations. Anchors provide a clean, fast, and removable fixation. In cracked, aged concrete, systems designed for that purpose must be chosen. Edge-near fastenings are installed only with sufficient edge distance; where this is not possible, the load is distributed through additional anchors or constructive measures.
Building gutting and concrete cutting
During gutting, temporary ladders, protective enclosures, cable runs, or guide rails must be fastened. Anchors enable short installation times and, after completion of the work, rapid removal. For precise cuts and safe guidance of equipment – also in combination with concrete demolition shears – controlled preload via defined torque is helpful.
Rock excavation and tunnel construction
In rock cavities and headings, anchors often serve to fix light brackets, work platform details, or safety nets. Due to inhomogeneous geology, load-bearing behavior is less predictable than in concrete. Local pull-out testing and conservative assumptions for load transfer are recommended. Moist and aggressive atmospheres argue for suitable materials with enhanced corrosion resistance.
Natural stone extraction
In natural stone extraction, anchors are primarily used for temporary fixings: markings, light guide fixtures, or securing service lines. Drilling must be performed in sound, unweathered rock. In heavily jointed areas, other methods are used.
Deconstruction, removal, and surface reinstatement
One advantage of anchors is their low-residue removal: After unscrewing, a borehole remains which, on exposed surfaces, can be filled and smoothed with a suitable mortar. Reuse of the same anchor at safety-relevant points is generally avoided. For temporary setups – for example when working with hydraulic splitters or concrete demolition shears – this contributes to short cycle times and orderly construction states.
Comparison with alternative anchoring systems
Compared to expansion anchors, anchors require no setting tool and create their anchorage via the cut thread. This reduces installation variables and often allows smaller edge distances. In comparison to bonded anchors, curing is eliminated; in return, drill-hole quality and torque control are critical. For very high loads, edge-near fixings with limited member thickness, or heavily cracked substrates, other systems can offer advantages. In deconstruction, anchors convince above all through speed, removability, and minimal surface rework.
Occupational safety, environmental influences, and documentation
During drilling and installation, personal protective equipment, dust extraction, and noise control must be considered. Moisture, de-icing salts, or chemical influences affect durability; material selection (e.g., zinc-plated or stainless) is made accordingly to the environment. Torques are documented, and critical fixings are tested on a sampling basis. Clear labeling of temporary anchorage points facilitates control during changing construction states.
Common mistakes in practice
- Incorrect drill diameter or insufficient drill-hole depth
- Inadequate hole cleaning; residual dust reduces capacity
- Undershooting edge and center-to-center distances
- Over-tightening the anchor due to excessive torque
- Installing in cracked concrete without a suitable anchor type
- Unsuitable material choice for moist or aggressive environments
- Missing documentation and no sampling tests
Practical references to Darda GmbH applications
In typical projects, anchors are used to fasten temporary brackets, guide fixtures, and protection systems to concrete when working with concrete demolition shears, hydraulic splitters, rock wedge splitters, combination shears, Multi Cutters, steel shears, or tank cutters. The goal is a safe, controlled work environment in which devices are precisely positioned, lines are neatly routed, and protection zones are clearly delineated.
Temporary anchorage points and auxiliary brackets
For anchorage points and auxiliary brackets at concrete edges or walls, anchors are often the first choice: short installation times, direct tightening, defined preload. After completion of the work, removal takes place and the surface is reinstated.
Guide fixtures when working with concrete demolition shears
When removing components with concrete demolition shears, firmly screwed guide fixtures support reproducible tool guidance. Anchors are arranged to maintain edge distances and avoid edge spalling.
Protection systems, barriers, and line routing
Anchors fix safety nets, barriers, and cable runs. In confined areas – for example in tunnel construction – the removable fastening is helpful for quickly adapting construction states.