Gas blasting is one of the controlled methods for releasing rock and concrete by generating targeted pressure. It is used when components must be separated with precision, vibrations minimized, and the surroundings protected. In practice it is often combined with hydraulic methods: cracks are initiated by gas blasting, then widened with stone and concrete splitters or, using concrete demolition shears, elements are further reduced by material type. This yields predictable results in areas such as concrete demolition and special demolition, rock excavation and tunnel construction, or natural stone extraction—even where conventional blasting or large-scale chiseling is not possible or not desired.
Definition: What is meant by gas blasting
Gas blasting is a method in which pressure is built up inside boreholes to induce and split cracks in rock or concrete in a controlled way. This is usually achieved by gas generation in a cartridge (gas-pressure based) or by volume-expansive media (e.g., chemical expansive agents). Unlike conventional blasting with high explosives, gas blasting is significantly more controlled, with lower vibration emission and reduced flyrock. It targets crack initiation and crack steering so that components fracture along a defined drilling pattern. In reinforced concrete, the mineral matrix is separated; the reinforcement initially remains bonded and can then be cut with concrete demolition shears, steel shears, or multi cutters.
How gas blasting works and its variants
Gas blasting leverages the fact that brittle-elastic materials like concrete and rock form cracks under internal overpressure. Critical parameters are borehole diameter, depth, spacing, and orientation relative to the desired crack line. The pressure is typically produced either by rapidly expanding gases or by media that press slowly and uniformly—each with specific pros and limits.
Gas-pressure-based systems
Cartridges or pressure tubes generate large gas volumes within fractions of a second. The pressure spreads radially in the borehole, locally exceeds the tensile strength of the material, and creates primary cracks that propagate along weakness planes. This variant is suitable for rock excavation and tunnel construction as well as massive concrete sections when rapid crack development is desired.
Volume-expansive media
Expansive agents are mixed and poured into boreholes. The expansion occurs with a delay and uniformly, enabling an especially low-vibration working mode. This variant is used, among others, for gutting works and cutting as well as in special demolition—for example in sensitive neighborhoods or heritage structures.
Crack steering and follow-up processing
The desired fracture line is defined by a drill pattern. After initial crack opening, mechanical finishing is often performed: stone and concrete splitters widen the formed cracks in a controlled manner, concrete demolition shears reduce isolated components, and steel shears or multi cutters cut exposed reinforcement or profiles. Depending on the task, hydraulic power packs serve as the central power source.
Planning: drill pattern, pressure level, and crack control
The quality of the outcome stands and falls with the design. Decisive factors are material properties (compressive and tensile strength, modulus of elasticity), component geometry, reinforcement ratio, and the target separation line.
Borehole parameters
- Diameter: depends on cartridge or expansive medium; small to medium diameters are typical for precise crack control.
- Depth: at least 70–90% of the member thickness to promote through-cracking; stepped drilling may be used in rock.
- Spacing: closer for high-strength/reinforced sections, wider for weaker material.
Crack initiation
- Boundary conditions: cracks seek the path of least resistance; free edges, predetermined breaking lines, and saw cuts support the path.
- Sequence: the activation order influences stress distribution and fracture pattern.
- Pre-relief: anchors, openings, or notches can reinforce the crack direction.
Limits due to reinforcement and inserts
Reinforcing steels, prestressing cables, mesh reinforcement, or embedded parts reduce crack-propagation speed. Frequently, the mineral matrix is separated by gas blasting and the remaining steel connection is then processed with concrete demolition shears, steel shears, or a cutting torch.
Areas of application and typical uses
Gas blasting is selected wherever targeted, low-vibration separations are required or where conventional blasting is not an option.
- Concrete demolition and special demolition: controlled release of massive foundations, bridge caps, or machine foundations; follow-up breaking with concrete demolition shears for single-grade separation.
- Gutting works and cutting: separating individual core zones; combining with sawing and shearing to form openings and reduce loads.
- Rock excavation and tunnel construction: advance, cross-section enlargement, invert and crown cuts under limited vibration thresholds.
- Natural stone extraction: gentle detachment of raw blocks along targeted crack lines; subsequent splitting with stone and concrete splitters to produce dimensionally accurate blocks.
- Special use: work in sensitive areas, e.g., near utilities, plants, traffic routes, or vibration-sensitive equipment.
Advantages and limits compared with hydraulic splitting and shears
Gas blasting provides a high crack-initiation performance at relatively low vibration levels and can initially remove coherence in heavily reinforced or thick sections. Hydraulic stone and concrete splitters then deliver a controlled crack widening with precisely metered force; concrete demolition shears make shape-accurate separations, downsize members to transport or sorting size, and expose reinforcement.
Limits of gas blasting include:
- Drilling effort: the required drill patterns are time- and equipment-intensive.
- Reinforcement: steel connections remain and must be mechanically cut.
- Edge distances: small edge zones require careful design to avoid spalling.
- Influences such as temperature and moisture: especially with expansive media, environmental conditions must be considered.
Workflow: from planning to post-processing
- Investigation: survey of material, reinforcement layout, embedded parts, and boundary conditions.
- Design: define drill pattern, sequence, and pressure level; saw cuts if needed for crack steering.
- Drilling: accurate production of boreholes, cleaning, and depth checks.
- Pressure application: introduce cartridges or expansive media; observe safety distances and shielding.
- Monitoring: observe crack opening and member behavior, keep records.
- Follow-up: crack widening with stone and concrete splitters; downsizing and sorting with concrete demolition shears; cutting metal with steel shears, multi cutters, or a cutting torch.
- Clearance: safe removal, transport, and material separation.
Safety, vibrations, and environmental influences
Gas blasting is designed for low vibrations but remains a method with potential hazards. General safety rules, suitable qualifications, and project-specific protection concepts apply. Statements here are always general and non-binding.
- Personnel protection: exclusion zones, shielding, safe ignition/activation procedures, protective clothing.
- Asset protection: vibration monitoring, protection against spalling, dust and noise reduction.
- Emissions: dust extraction, localized wetting, control of gas release; consider exhaust gases and pressure waves.
- Neighborhood: information management, compliance with quiet times and vibration limits per local practice.
Quality assurance and documentation
A reproducible result arises from documented planning and control. Key inspection and verification elements are:
- Drilling logs: diameter, depth, location, count, deviations from the drill pattern.
- Pressure/quantity data: parameters of cartridges or media used, activation times.
- Crack pattern documentation: course and width checks, photo documentation, measurement points.
- Vibration data: measured values, comparison with target and limit values.
- Follow-up: use and parameters of stone and concrete splitters and concrete demolition shears to complete the separation as planned.
Economic and organizational aspects
The cost-effectiveness of gas blasting is determined by drilling performance, media consumption, cycle times, and the quality of follow-up work. In complex projects, efficiency arises from the combination of methods: gas blasting for crack initiation, hydraulic splitting for controlled opening, concrete demolition shears and steel shears for single-grade separation. Hydraulic power packs consolidate drive capacities and simplify logistical coordination in confined spaces, for example in tunnel construction or during gutting works.
Practical recommendations for the combination with stone and concrete splitters and concrete demolition shears
- Pre-planning the interfaces: choose drill patterns so that wedge splitting and shear access points have clear attack surfaces.
- Control crack width: design gas blasting for crack initiation; perform the actual opening with force- and displacement-controlled stone and concrete splitters.
- Handle reinforcement: after exposure, switch quickly to concrete demolition shears and steel shears to avoid downtime.
- Secure component removal: plan load paths, provide temporary shoring, define the sequence clearly.
- Material cycles: size reduction to sortable fractions to optimize processing and haulage.
Assess material and boundary conditions correctly
Concrete strength, aggregate, moisture, temperature, and reinforcement ratio have a noticeable influence on the result. Rock types behave differently: anisotropic rocks (foliation, joints) steer cracks; homogeneous hard rocks require a tighter drill pattern and higher pressure level. In all cases, a test-calibrated design improves the prediction of crack patterns and cycle time.
Example workflows in the application areas
Concrete demolition and special demolition
Massive foundations: drill pattern along the intended break line, gas blasting for decoupling, crack widening with stone and concrete splitters, shear-based downsizing and reinforcement cutting to transport size.
Rock excavation and tunnel construction
Cross-section enlargement: staggered drill pattern, gas-pressure-based crack initiation, sectional follow-up splitting, targeted release of blocks, material removal in short cycles at low vibration values.
Natural stone extraction
Block recovery: crack guidance along structural planes, time-staggered activation, mechanical widening, dimensionally accurate detachment of raw blocks.