Prestressing steel is a central component of modern concrete construction. It enables highly load-bearing yet slender structures that are used in bridges, parking structures, silos, tank structures, beams, and slabs made of prestressed concrete. For concrete demolition and special deconstruction, understanding prestressing steel is essential because the energy stored in tendons must be controlled in a targeted manner. Methods such as selective breaking with concrete pulverizers or controlled splitting with rock and concrete splitters, driven by hydraulic power packs, are used to expose, de-tension, and safely sever tendons.
Definition: What is meant by prestressing steel
Prestressing steel is a high-strength steel used for prestressing concrete. It is used as wire, strand (twisted individual wires), or bar to introduce a defined prestressing force into a component. This prestress generates compressive stresses in the concrete that compensate for tensile stresses from service loads. A distinction is made between pre-tensioned systems (bonded prestressing) and post-tensioned systems (unbonded prestressing or grouted afterwards). Characteristic features include high strength, limited relaxation, suitable surface characteristics, and defined strain properties. In practice, tendons are routed in ducts, anchored, and—depending on the system—grouted.
Types, properties, and manufacture of prestressing steel
Prestressing steel is cold-drawn, cold-worked, or heat-treated to achieve high tensile strengths and low relaxation. Typical forms are:
- Wire: smooth or profiled single wire, often for precast prestressed concrete elements
- Strand: several wires twisted into a tendon, widely used in bridge and building construction
- Bar: solid bar with thread options for defined anchorage solutions
Key characteristics are yield strength, tensile strength, elongation at break, relaxation behavior, and notch sensitivity. Surfaces may be smooth, ribbed, or indented to influence bond and anchorage behavior. Residual manufacturing stresses, corrosion protection (e.g., by greases, waxes, or grout in the duct), and end anchorages determine in-service behavior. For deconstruction, anchorage zones, the routing of ducts, possible deviators, and the grout condition (grouted/ungrouted) are particularly relevant, as they govern the cutting concept and accessibility.
Prestressing steel in deconstruction: risks, planning, and occupational safety
Prestressing steel stores potential energy. When cutting, this energy can be released suddenly. A robust deconstruction concept avoids uncontrolled releases and limits consequential damage to adjacent components.
- Hazard: snap-back of strands/wires, uncontrolled cracking of components, tool jamming
- Planning: as-built analysis, detection of tendons, definition of cutting sequence, safety distances, shielding
- Organization: qualified specialists, permit-to-work processes, coordination with structural engineering and site management
- Technology: use of suitable hydraulic tools, redundant load transfer, staged de-tensioning
In sensitive areas with vibration and noise restrictions, hydraulic methods with high controllability are often preferred. Concrete pulverizers allow targeted removal of concrete cover to expose tendons. Stone and concrete splitters create defined separation joints and reduce restraint, for example when components are to be isolated from one another before de-tensioning. Hydraulic power packs supply these tools with the required power.
Exposing tendons: gentle procedures
Before cutting, the prestressing steel must be accessible. The rule is: remove concrete cover locally, in a controlled manner, and with minimal intervention.
- Pre-investigation: review of drawings and on-site probing accompanying the works
- Detection: identification of ducts, anchorages, couplers, and deviators
- Removal: use of concrete pulverizers to progressively break the concrete cover without significant vibration
- Relieving: stone and concrete splitters to create controlled separation joints to decouple components before de-tensioning
After exposure, tendons are cleaned and secured against unintended movement. For ungrouted ducts, be alert to any escaping media. Protective devices and shielding reduce risk during the subsequent cut.
Cutting and de-tensioning prestressing steel: methods and tool selection
The choice of method is guided by accessibility, cross-section, prestressing force, and environmental requirements.
- Hydraulic steel shears: precise shearing of wires, strands, and bars, also in combination shears for accompanying cutting of reinforcement
- Multi cutters: versatile cutting of mixed materials when tendons occur together with reinforcement
- Concrete pulverizers: preparatory opening of ducts, exposing anchorage zones, and controlled reduction of concrete cross-sections
- Stone and concrete splitters: create separation joints for step-by-step decoupling of components prior to the actual cut
With high residual prestress, work is performed in several stages: set up protection, re-route load paths, first cuts in edge areas, intermediate fixation, complete severing. Never cut without verification of load paths and without consulting the structural engineer.
Special structures with prestressing steel: bridges, parking structures, silos, and prestressed concrete slabs
Prestressing steel is used where large spans, high loads, or small structural depths are required.
- Bridges and viaducts: hollow core girders, box girders, external prestressing steel
- Parking structures: flat slabs with post-tensioning, deck slabs
- Silos and tank structures made of prestressed concrete: circumferential prestressing, anchorage zones with increased steel concentration
- Beams and slabs in building construction: prestressed to limit deflection and crack widths
The deconstruction procedure varies by system: For internal tendons, opening the ducts and controlled de-tensioning are paramount. For external tendons, accessibility and securing free strand lengths are decisive. Concrete pulverizers and hydraulic steel shears have proven effective for exposing and cutting, while stone and concrete splitters support structural decoupling before the actual cut.
Common damage patterns and their impact on deconstruction
Corrosion, wire breaks, insufficient grouting, and faulty anchorages or deviators influence behavior during cutting.
- Corrosion/cross-section loss: lower residual load-bearing capacity, but possibly uneven stress distribution
- Ungrouted ducts: free strand lengths may snap back during cutting
- Anchorage zones: locally high steel concentration, special protective measures required
- Deviators: increased friction and possible notch effects
An adapted strategy with step-by-step exposure, securing, and cutting—supported by concrete pulverizers and multi cutters—minimizes unforeseen effects. Stone and concrete splitters help separate components so that stresses do not redistribute uncontrollably.
Practical guide: sequence for selective concrete demolition with prestressing steel
- Survey: review documents, on-site checks, detection of tendons
- Risk assessment: identify hazards, define safety and containment zones
- Cutting concept: define sequence, secure load paths, provide temporary shoring
- Exposure: remove cover concrete with concrete pulverizers, open ducts, make anchorages accessible
- Decoupling: create joints with stone and concrete splitters, reduce restraint
- Partial de-tensioning: staged cutting with hydraulic steel shears or combination shears, intermediate fixation
- Complete severing: defined cutting path, controlled removal, continuous monitoring
- Follow-up: secure cut interfaces, prepare disposal, compile documentation
Quality assurance and documentation
Robust documentation includes the location of tendons, the tools used, the cutting sequence, and the protective measures taken. Measurement and observation data (e.g., deformations, cracking) are recorded continuously. Hydraulic power packs and tools must be checked before use; visual inspections, functional tests, and maintenance records increase process reliability.
Legal and organizational notes
Planning and execution follow the relevant technical regulations. Responsibilities and approvals must be clearly assigned. The statements in this article are general and do not replace project-specific planning. For work on load-bearing components with prestressing steel, the involvement of qualified specialist designers and experts is required.
Demarcation: prestressing steel in the context of other application areas
In application areas such as strip-out and cutting, prestressing steel typically becomes relevant only in load-bearing structures. In rock demolition and tunnel construction or natural stone extraction, the focus is on blasting-free and low-vibration splitting of rock; here, stone and concrete splitters are used independently of prestressing steel. For special operations, methods must be selected to comply with environmental conditions—such as vibration and noise control.
Tool interplay when working with prestressing steel
Concrete pulverizers
For precise removal of concrete cover, opening ducts, and exposing anchorage zones. Controlled breaking keeps tendons visible and accessible.
Stone and concrete splitters
For creating defined separation joints and decoupling components before tendons are severed. This reduces restraint and facilitates staged de-tensioning.
Steel shears, combination shears, and multi cutters
For cutting wires, strands, bars, and accompanying reinforcement. The selection depends on cross-section, material, and accessibility. Hydraulic power packs provide the required power for uniform cuts.