Surface cracks shape the appearance of concrete, natural stone, and metal and significantly influence planning, execution, and safety in deconstruction, cutting, and non-explosive splitting. In practice—from concrete demolition and building gutting to rock breakout—they are both an opportunity and a risk: they can act as natural parting planes and reduce working energy, yet also promote uncontrolled spalling, crack propagation, or leakage. Those who understand crack causes, propagation paths, and activity can purposefully select tools such as a concrete pulverizer or hydraulic rock and concrete splitters and control separation processes precisely.
Definition: What is meant by surface crack
A surface crack is a linear material separation in the immediate vicinity of the component surface. It ranges from finest hairline cracks to clearly opened separation cracks, can be locally limited or net-like, and preferentially follows weaker zones (pores, microstructure boundaries, reinforcement edge). Surface cracks arise due to volume changes (shrinkage, temperature), mechanical loading (load cycles, impact), physico-chemical processes (corrosion, alkali–silica reaction), or processing influences (drilling, cutting). In deconstruction, they indicate the required forces, the crack width, and potential guidance of controlled fracture lines.
Causes and formation of surface cracks
The formation of surface cracks follows the interplay of material, climate, geometry, and loading. Decisive is the restraint of deformations in the edge zone: where the material wants to move but cannot, stresses build up and are released as cracks.
Concrete: shrinkage, temperature, and load stresses
Early shrinkage cracks arise from drying or plastic shrinkage, often as a fine, net-like crack pattern. Temperature gradients—e.g., from heat of hydration and cooling—lead to near-surface tensile stresses. Under service loads, transverse or longitudinal cracks form, preferably at notches, openings, and edges. Corrosion of the reinforcement drives cracks parallel to the bar axis; alkali–silica reaction produces a characteristic, wide-meshed crack network. Freeze–thaw cycles promote spalling in the cover layer.
Natural stone and rock: fabric and discontinuities
In natural stone, geological discontinuities (joints, bedding, foliation) dominate. Stress relief at exposed faces, weathering, and frost produce near-surface shell and edge cracks. Drilling and blasting vibrations as well as mechanical processing create additional microcracks. For rock demolition and tunnel construction and for natural stone extraction, these crack systems are the natural guidance for controlled fractures.
Steel and tanks: edge-zone crack initiations
In metals, near-surface crack initiations occur due to notch effects, weld transitions, grinding structures, work hardening, or stress corrosion cracking. When cutting with a steel shear or a tank cutter, crack position is relevant because initiations can propagate under cutting load and affect tightness, fire protection, and explosion protection.
Detection and assessment
A systematic crack survey improves tool selection, reduces emissions, and increases occupational safety. Visual inspection comes first, supplemented by simple test and measurement steps.
- Visual inspection in raking light after cleaning; mark crack start, end, and direction
- Classification of crack width (from hairline crack to opened separation crack) with a crack gauge
- Mapping: crack course, crack spacing, and relation to edges, openings, built-in components
- Concrete: tapping, moisture indication, and, where accessible, endoscopy at edge zones
- Steel: dye penetrant or magnetic particle testing for near-surface crack initiations
- Monitoring: plaster markers, strain gauges, or photographic documentation to assess activity
For deconstruction, cause, position relative to the load path, and proximity to planned cutting or splitting lines are decisive. The more active a crack, the more conservatively the work sequence should be chosen.
Influence on concrete demolition, building gutting, and cutting
Surface cracks alter load paths and edge stability. This affects force demand, sequence, and safeguarding measures—both in the demolition of massive components and during building gutting and cutting in existing structures.
Targeted use of surface cracks
- As natural parting planes for stone and concrete splitters and rock wedge splitter to guide controlled fracture lines
- As an engagement point for a concrete pulverizer to break cover layers and expose reinforcement
- To reduce pressing and cutting forces as well as noise, dust, and vibrations
Minimizing risks
- Spalling risk at crack-penetrated edges: protective measures and suitable holding and shoring concepts
- Undesired crack propagation: install stop holes or adjust the sequence of interventions
- Influence on neighboring components: prefer low vibration levels methods and consider load reserves
Tool selection and parameters
The crack situation guides the choice of separation and splitting technology and its settings. The goal is a controlled, reproducible fracture with minimal secondary effects.
- Concrete pulverizer: advantageous at near-edge cracks and for opening the cover layer; crack lines serve as engagement points
- Stone and concrete splitters or rock wedge splitter: non-explosive, low-vibration splitting along existing crack systems
- Combination shears and multi cutters: suitable for composite cross-sections of concrete and metal with overlapping crack patterns
- Steel shear: when crack initiations in steel sections affect cutting guidance and remaining cross-sections
- Tank cutter: for vessels and plates with crack initiations; controlled, low-spark cutting strategies support safety
- Hydraulic power pack: stable pressure and flow supply for reproducible crack initiation and controlled stroke sequences
Parameters such as pressing pressure, number of strokes, pilot bore diameter, and cutting sequence must be adapted to crack width, component thickness, reinforcement ratio, and environmental requirements.
Targeted crack initiation for controlled separation
Crack lines can be defined through preparatory measures and then extended with hydraulic splitting or shear technology. This increases the predictability of the fracture path.
- Define the splitting or cutting line and document it with reference points
- Series drilling along the line: center-to-center spacing to create a weakened web
- Use of stone and concrete splitters or rock wedge splitter to initiate cracks in the boreholes
- Follow-up with a concrete pulverizer or multi cutters for remaining cross-sections
- Crack control using stop holes and edge relief if the course deviates
This approach is established in concrete demolition and special demolition, in rock breakout and tunnel construction, as well as in natural stone extraction, because it limits emissions and improves environmental compatibility.
Repair, securing, or deconstruction?
Whether surface cracks should be repaired or components selectively separated depends on function, crack activity, and use. General, non-binding guiding thoughts help with classification:
- Inactive hairline cracks without functional impairment: often tolerable or treatable with surface protection
- Cracks that promote moisture ingress or corrosion: consider sealing or injection; check critically if load-bearing
- Extensive crack networks (e.g., due to chemical reactions): often an indication of substance loss—selective deconstruction is plausible
- Safety-relevant components or media containers: proceed conservatively; separating and renewing may be appropriate
Within building gutting and cutting, crack position governs the sequence, temporary shoring, and the choice between splitting, pulverizer, or shear techniques.
Occupational safety, emissions, and environmental protection
Surface cracks influence stability and fracture dynamics. Accordingly, protective and environmental measures must be aligned with the crack situation.
- Cordon off crack-prone zones; provide protection against falling slabs
- Vibration and noise reduction: hydraulic splitting and pulverizer work are generally associated with low vibration levels
- Special operations in sensitive areas: monitoring of vibrations and dust, work sequences adapted to the surroundings
- Metals and tanks: fire protection and explosion protection; crack initiations can intensify leak paths or notch effects
Material and geometry influence
Crack tendency and course depend on edge-zone quality, component geometry, and microstructure. These factors determine how well surface cracks can be used or need to be secured.
Concrete edge zones
The concrete cover reacts sensitively to shrinkage and temperature. Surface cracks preferentially develop along reinforcement and at edges. Splitting and cutting lines should account for these edge zones to avoid undesired spalling.
Edges, openings, and built-in components
Notch effects concentrate stresses and promote crack formation. For the engagement of a concrete pulverizer and splitting wedges these locations are effective but require additional safeguarding.
Rock joints and bedding
In rock, joint orientations and bedding govern fracture readiness. Along these structures, stone and concrete splitters work particularly efficiently and with low vibration levels.
Documentation and quality assurance in the project workflow
Clear documentation of the crack situation before, during, and after the work creates transparency and repeatable quality.
- Crack maps with width indications and scaled photo documentation
- Logs of pressing pressures, stroke sequences, drilling parameters, and cutting sequences
- Acceptance criteria for residual surface quality and permissible crack patterns
- Comparison of planning with the actual crack course to optimize subsequent steps