Strength Class in Concrete, Rock & Steel

The strength class describes the load-bearing and resistant properties of a material under defined test conditions. For planning, execution, and deconstruction of structures, it is a key parameter: it influences the choice of methods, tools, and parameters—from controlled concrete demolition with concrete demolition shears to low-vibration splitting with rock and concrete splitters. Correct interpretation of material parameters reduces risks, shortens working times, and improves result quality in the application areas of concrete demolition and special demolition, strip-out and cutting, rock excavation and tunnel construction, natural stone extraction, and special operations.

Definition: What is meant by strength class

A strength class is a normatively defined categorization of material strength, usually referring to compressive strength (e.g., concrete and natural stone) or tensile strength or yield strength (e.g., steel). The class assignment results from standardized test procedures (e.g., cylinder compressive strength for concrete, uniaxial compressive strength for rock, tensile test for steel). In practice, the strength class directly affects the choice of deconstruction method: higher strengths require different tools, altered work sequences, adjusted hydraulic power, and often differentiated preparations such as drilling patterns or pre-cuts.

Classification of concrete strength classes according to EN 206

In concrete construction, the strength class according to EN 206 is specified with the scheme Cx/y. Here, x denotes the cylinder compressive strength (in MPa) and y the cube compressive strength. Common classes are C16/20, C20/25, C25/30, C30/37, C35/45, C40/50 up to high-strength concretes such as C50/60 and higher. As the class increases, concrete hardness and abrasion resistance increase, often accompanied by denser aggregate grading and lower pore space.

For deconstruction, this means:

Lower classes (e.g., C16/20, C20/25) can typically be pre-crushed more quickly with concrete demolition shears; edge break and spalling occur more readily, which facilitates opening cross-sections.
Medium classes (e.g., C25/30 to C35/45) require more precise targeting at material weaknesses, joints, and edges. A combination of a concrete demolition shear and subsequent splitting can reduce process time.
Higher classes (e.g., C40/50 and upwards) are tough; ductile reinforcement can impede fracture. Rock and concrete splitters produce targeted crack guidance along drilled axes and work with low vibration—advantageous in sensitive environments.

Strength classes of natural stone and rock (uniaxial compressive strength)

For natural stone and rock, classification is based on uniaxial compressive strength (UCS). It ranges from soft rock (low MPa values) to very strong rock (well above 100 MPa). Additionally, bedding, jointing, water content, and mineral composition influence fracture behavior. For rock excavation and tunnel construction as well as natural stone extraction, these parameters are decisive.

Impact on process engineering

Isotropic, homogeneous rock: Controlled crack propagation with rock and concrete splitters via an adapted drilling pattern (diameter, spacing, depth).
Foliated or jointed structures: Use of natural planes of weakness; lower hydraulic power may suffice, but borehole positioning is more critical.
Very high strengths: Tighter drilling patterns, staged pressure cycles, and sequential splitting enable controlled blocks instead of uncontrolled fragmentation.

Strength classes of steel and reinforcement

For steels, classes are often defined by yield strength and tensile strength (e.g., S235, S355, S460). Reinforcing steels in concrete construction are typically classified as B500. With increasing strength, the demands on cutting and separation techniques rise. In the deconstruction of reinforced concrete, reinforcement strength directly influences the choice of concrete demolition shear (jaw opening, blade geometry) and, if necessary, the complementary use of steel shears or multi cutters.

Consequences in deconstruction

Concrete demolition shears separate the concrete matrix and snip or cut reinforcement. For higher-strength reinforcement, optimized blade profiles and sufficient hydraulic forces are crucial.
Pure steel components (sections, tanks, vessels) require cutting processes; depending on wall thickness, steel shears or a Tank Cutter may be suitable.

Influence of the strength class on deconstruction methods and tool selection

The strength class governs how efficiently a material can be separated, broken, or split. It is therefore the guiding parameter for the selection of concrete demolition shears, rock and concrete splitters, combination shears, steel shears, and supplementary hydraulic power packs.

Concrete demolition and special demolition

Concrete demolition shears: Advantageous for cross-section reduction, demolition edges, and exposing reinforcement. With increasing concrete strength, defined attack points (joints, notches, core drillings) are decisive.
Rock and concrete splitters: Particularly suitable for high-strength or thick members when vibrations, noise, and dust must be limited. Cracks are initiated in a targeted way along a drilling pattern.

Strip-out and cutting

For mixed constructions with different strengths, a sequential approach is recommended: pre-separating steel portions (steel shears), followed by concrete break-up (concrete demolition shear) or splitting.

Rock excavation and tunnel construction

With increasing rock strength, the need for precise drilling pattern planning rises. Splitters are a low-vibration alternative when vibrations must be limited.

Determination and assessment of the strength class in practice

Reliable assignment of the strength class forms the basis of every deconstruction plan. In practice, document review and test procedures are used, and their results are compared with experience.

Documents and existing conditions

Drawings, structural analysis, and material documentation provide initial indications (concrete mixes, reinforcement ratio, steel grade).
Year of construction and use provide clues for typical classes and possible inhomogeneities (recompaction, post-treatments, refurbishments).

In-situ methods

Rebound hammer and ultrasonic measurements provide indicative values for concrete strength.
Cores with laboratory testing allow a robust assignment and show fabric, porosity, and any damage.
For rock: point load index and, if required, laboratory tests for uniaxial compressive strength.

Drilling pattern, crack guidance, and sequence in splitting

When splitting concrete and rock, the drilling pattern and the work sequence are crucial for controlled crack propagation. The strength class defines how closely the boreholes should be spaced, which diameters are sensible, and in which stages pressure is applied.

Principles for efficient splitting

Borehole orientation along existing planes of weakness (joints, edges, bedding).
Adjusted spacing: higher strengths generally require smaller spacing.
Sequential pressure cycles: several passes with moderate pressure increases improve crack control.

Strength class and concrete demolition shears: practical selection criteria

The performance of a concrete demolition shear is determined by jaw opening, crushing force, and blade geometry. As concrete strength and reinforcement strength increase, targeted preparations become more important.

Practical notes

Create attack points: preferably start at edges, openings, predetermined breaking points, or pre-cut areas.
Keep reinforcement in view: higher reinforcement ratios and strengths require more robust blades and, if necessary, supplementary steel cutting methods.
Hydraulic reserve: sufficient system pressure and flow via suitable hydraulic power units ensure continuous performance.

Rock and concrete splitters: application by strength class

Splitters generate a controlled, directed blasting effect via hydraulic wedges without explosives. They are predestined for high strengths, massive cross-sections, and sensitive environments.

Advantages at higher strengths

Targeted crack formation: plannable block sizes and crack paths even in C40/50+ or very strong natural stone.
Minimized secondary damage: low vibrations and reduced noise facilitate work in interior areas and on existing structures.
Combinability: pre- or post-operations with concrete demolition shears enable an efficient overall concept.

Fields of application: examples and procedures

Concrete demolition and special demolition: For medium strengths, the combination of a concrete demolition shear (exposing, downsizing) and a splitter (controlled separation of thick members) accelerates the process.
Strip-out and cutting: Different strengths in composite members (concrete/steel) require coordinated separation of the materials; concrete demolition shears and steel shears are used sequentially.
Rock excavation and tunnel construction: High rock strengths demand precise drilling patterns; splitters enable low-vibration advance and block release.
Natural stone extraction: The strength class and jointing determine hole spacing and wedge selection; the goal is defined raw blocks with minimal waste.
Special operations: In areas with strict emission limits (vibration, dust, noise), splitting methods offer advantages regardless of the strength class.

Material condition and additional factors

In addition to the strength class, further factors influence demolition behavior: moisture content, aging (e.g., carbonation), temperature, and fabric defects. In concrete, reinforcement ratio, fiber content, and aggregate have a strong effect on fracture behavior. These influences should be incorporated into the choice of method and parameterization of concrete demolition shears as well as rock and concrete splitters.

Practice-oriented reference values and decision logic

Without stating binding numbers, a robust decision logic can be derived:

Low to medium concrete strength: open the concrete primarily with shears, cut reinforcement, split remaining cross-sections depending on member thickness.
High concrete strength or thick cross-sections: prepare splitting (drilling pattern), then remove with the concrete demolition shear; with high steel content, additionally use steel shears or multi cutters.
Rock/natural stone: plan splitting based on the fabric structure; in anisotropic rock, guide cracks along the natural planes.

Safety, environmental, and permitting aspects

The choice of method should always consider occupational safety, emissions, and component protection. Splitting methods are often advantageous when vibrations and noise must be limited. Requirements can vary regionally; careful alignment with the boundary conditions is advisable.

Planning, documentation, and quality assurance

Clean documentation of the strength class, the selected methods, and the achieved results creates transparency and reproducibility. This includes drilling patterns, hydraulic parameters used, sequences of concrete demolition shear operations, and the actual fracture pattern. With these data, future projects can be planned more precisely and the tool selection—from concrete demolition shears through rock and concrete splitters to steel shears or tank cutters—can be specifically optimized.

Note: Where strength classes are not clearly known, cautious parameterization with gradual power increase as well as the combination of indicative tests and experience is recommended.