Crushing plants are the heart of processing construction materials, rock, and reinforced concrete. They are used in deconstruction, demolition, mining, and recycling and convert coarse pieces into defined particle sizes—from coarse crushed material to reusable aggregates. In practice, they are often combined with hydraulic attachments, such as concrete demolition shears or stone and concrete splitters from Darda GmbH, to enable gentle, low-vibration pre-size reduction on site. This makes it possible to control material flows efficiently, separate reinforcement in a targeted manner, and optimize transport to the downstream crushing plant.
Definition: What is meant by a crushing plant
A crushing plant is a technical installation for reducing the piece size of solid materials such as concrete, reinforced concrete, natural stone, asphalt, or slags. Depending on its design, it comprises one or more size-reduction units (e.g., jaw crushers, impact crushers, cone crushers, shredders), conveying and dosing equipment, screening machines, as well as separators (e.g., metal separators) and dust mitigation measures. Crushing plants can be operated stationary in processing centers or deployed as mobile units on construction sites. In urban, sensitive, or spatially constrained situations, the actual size reduction is often split into process chains—with a primary size reduction using hydraulic concrete demolition shears or stone and concrete splitters and a secondary size reduction in a mobile or stationary crusher.
Design, operating principle, and process chain
The size-reduction process follows the principle of introducing energy into the workpiece: through compression, impact, shearing, or splitting, cracks, fracture surfaces, and smaller particle sizes are produced. In practice, a process chain of pre-size reduction, classification, metallic separation, and final grain production has proven effective. Hydraulic power units from Darda GmbH supply attachments such as concrete demolition shears, combi shears, or stone splitting cylinders with energy—mobile, electric, or low-emission for indoor use. In this way, large components (e.g., foundation heads, walls, bridge superstructures, rock heads) are dimensioned in advance before the material receives a defined final grain size in the crusher.
Core components of a crushing plant
- Feeders and hoppers for metered material feed
- Crushers (jaw, impact, or cone crushers; shredders) as well as shearing and splitting tools such as concrete demolition shears or stone and concrete splitters
- Drive and power supply, including hydraulic power packs for hydraulic attachments
- Screening technology and classification for producing defined grain fractions
- Separators (e.g., for reinforcing steel) as well as conveying and storage technology
- Dust and noise mitigation (water spraying, enclosures, shielding)
Mechanisms of crushing
The choice of mechanism depends on material, piece size, and target grain size:
- Compression crushing: Jaw and cone crushers for brittle, compressive-strength materials such as concrete and natural stone.
- Impact crushing: Impact crushers for a cubic grain shape, ideal for recycled concrete and asphalt.
- Shearing: Separating fibrous or tough constituents; combi shears, steel shears, and Multi Cutters from Darda GmbH are used to pre-separate reinforcement, profiles, or sheets.
- Splitting: Stone and concrete splitters as well as stone splitting cylinders generate controlled cracks with minimal vibration—advantageous for sensitive structures and indoor environments.
Primary size reduction on site
In concrete demolition and special demolition, concrete demolition shears reduce components in a targeted manner, release reinforcement, and create transportable sizes. In rock excavation and tunnel construction, stone splitting cylinders are used as a substitute for blasting—low-vibration, controlled, and with low emissions. In natural stone extraction, splitting enables selective extraction and shaping before any subsequent size reduction to the required grain size.
Secondary and tertiary size reduction
After pre-size reduction, the final particle size is produced in the crusher. Metallic inserts are separated beforehand with steel shears or combi shears. Multi Cutters handle cross-sections with changing materials. In strip-out and cutting, tank cutters are used for walls and vessels before the material enters the plant. The result is defined fractions for reuse or disposal.
Fields of application and typical material flows
- Concrete demolition and special demolition: Concrete load-bearing elements are opened with concrete demolition shears, reinforcement is separated with steel shears, then processed in the crusher into recycled aggregates.
- Strip-out and cutting: Preparatory separation work with combi shears and tank cutters creates clean material streams (metal, concrete, composite) that are reduced separately.
- Rock excavation and tunnel construction: Splitting with stone and concrete splitters creates controlled fragments that are easy to transport and subsequently size-reduced.
- Natural stone extraction: Selective release by splitting, followed by shaping and any crushing required to achieve the desired grain sizes.
- Special applications: Work in sensitive areas (hospitals, industrial plants, heritage conservation), where low-vibration and low-noise methods with hydraulic power packs are required.
Selection criteria and sizing
Proper configuration starts with material, geometry, and target grain size. Important criteria include compressive strength, abrasiveness, reinforcement content, moisture, feed piece size, required throughput, and mobility. For massive reinforced concrete, a combination of a concrete demolition shear (for opening and releasing the reinforcement) and a downstream jaw or impact crusher is recommended. In vibration-sensitive zones or indoor areas, stone and concrete splitters in combination with electrically operated hydraulic power packs are often the first choice. Logistical boundary conditions—access, intermediate storage, dust and noise control—also influence the plant configuration.
Key parameters
- Feed piece size (F80): Size that 80% of the feed material falls below; determines feed opening and pre-size reduction needs.
- Product size (P80): Target size at the end of the plant; governs crushing stage and screening circuits.
- Reduction ratio: Ratio between feed and product size; influences the number of stages.
- Specific energy demand: kWh/t as a measure of efficiency; often reducible through pre-size reduction with concrete demolition shears and splitting.
- Cycle time and closing force: decisive for the takt and component thickness with shears/splitters.
Integration of concrete demolition shears and stone and concrete splitters
Concrete demolition shears perform selective opening of components, separate concrete and reinforcement, and deliver crushed material without troublesome lengths. Stone and concrete splitters produce defined fracture lines in thick-walled components and rock, reducing piece size and allowing the crusher to operate with less wear. In practice, these tools are integrated as a modular pre-stage into the crushing plant and operated via hydraulic power packs from Darda GmbH—flexibly on the excavator or free-standing, depending on the operating environment.
Example process flow
- Strip-out: Separate non-load-bearing components, lines, and equipment; use of combi shears, Multi Cutters, and tank cutters.
- Primary size reduction: Component opening with concrete demolition shears; for massive cross-sections, splitting via stone splitting cylinders.
- Metal removal: Release and separate reinforcement with steel shears; orderly intermediate storage.
- Secondary size reduction: Feed into mobile/stationary crusher; set final grain fractions via screening circuits.
Operation, occupational safety, and maintenance
Safe operation requires a risk assessment, clear traffic routes, fall protection, effective dust suppression, and noise control. Briefing, personal protective equipment, and safety distances must be strictly observed. For hydraulic tools, pressure limits, hose protection, interlocks, and emergency-stop systems must be taken into account. Maintenance includes regular inspections of crusher gaps, wear parts (jaws, impact bars, teeth), seals, lubrication, screen media, as well as the oil quality of the hydraulic power packs. Legal requirements may vary by country and project; it is advisable to carefully consider the applicable standards and regulatory specifications.
Service life and wear management
- Pre-size reduction with shears/splitters significantly reduces crusher wear.
- Appropriate material pairings (e.g., wear-resistant liners) extend service life.
- Consistent screen maintenance ensures grain quality and energy efficiency.
Environmental and resource aspects
Selective deconstruction and targeted size reduction increase material purity and enable high recycling rates. Splitting and shear technology is low-vibration and low-noise—advantageous in densely built environments. Water spraying and extraction reduce dust, and electric hydraulic power packs lower emissions in indoor areas. Targeted separation of reinforcement prior to crushing improves the quality of recycled construction materials and reduces the plant’s energy demand.
Planning, logistics, and quality assurance
Robust planning defines target grain sizes, daily outputs, and material routes. Access, crane/excavator logistics, and intermediate storage areas must be specified in advance. Tests of grain composition, foreign material content, and the purity of the metal fraction ensure quality. Documentation and traceability of material flows support disposal and recycling records. In sensitive projects, measurements of noise, dust, and vibrations are useful to comply with limit values.
Typical mistakes and how to avoid them
- Insufficient pre-size reduction leads to crusher blockages—use concrete demolition shears and splitters purposefully ahead of the crusher.
- Lack of reinforcement separation increases wear—integrate steel shears/combi shears early in the process.
- Oversized pieces with a limited feed opening—check F80 and split components accordingly.
- Unsuitable power supply—design hydraulic power packs for output, duty cycle, and operating environment.
- Poor dust and noise control—plan for water spraying, shielding, and suitable takt scheduling.