Quantity calculation is a central foundation for planning, estimating, and executing works in concrete demolition, special demolition, rock excavation, and natural stone extraction. Those who reliably determine volumes, mass, quantities, and reinforcement ratios lay the groundwork for equipment deployment, takt planning, the selection of suitable methods, and logistical handling including disposal. Especially for mechanical methods such as splitting and fragmenting with hydraulic rock and concrete splitters or gripping and separating with concrete pulverizer, time requirements and occupational safety directly depend on realistic quantity allowances.
Definition: What is meant by quantity calculation
Quantity calculation is the systematic determination of quantitative parameters required for planning and executing construction, demolition, and extraction works. These include volume (m³), mass (t), lengths (m), areas (m²), unit counts (pcs.), and material shares (e.g., reinforcing steel in kg/m³). In the fields of concrete demolition and special demolition, gutting works and concrete cutting, rock excavation and tunnel construction, natural stone extraction, and special demolition, quantity calculation merges geometric models, material properties, and work methods into robust numerical values.
Methods and calculation paths of quantity calculation
In practice, simple solid formulas, composite geometries, as-built measurement methods, and model-based approaches (e.g., from record drawings or 3D scans) are used. For reinforced concrete elements, volumes are typically derived from member thicknesses and areas, reinforcement ratios from experience or drawings. In rock removal, cubic capacities are determined from profiles, drilling or cutting patterns, including allowances for overbreak or underbreak. The choice of method depends on required accuracy, data availability, and the selected mechanical method—such as splitting with hydraulic wedge splitter or fragmenting with concrete pulverizer.
Fundamentals: Units, densities, and typical key values
Reliable base constants are the prerequisite for dependable calculations. Typical densities at practical moisture are approximately: normal concrete 2.30–2.50 t/m³, reinforced concrete 2.40–2.60 t/m³, reinforcing steel 7.85 t/m³, hard rock (granite/gneiss) 2.60–2.80 t/m³, limestone 2.40–2.70 t/m³. For quantity calculation, openings, recesses, and cavities are deducted, and allowances for fracture edges, oversize, and screen loss are considered.
Quantity calculation in concrete demolition: elements, volume, and reinforcement
For reinforced concrete members, volume is frequently derived from standardized geometries. The resulting mass influences the selection of demolition sequences as well as the sizing of concrete pulverizer, hydraulic power pack, and lifting devices.
Typical elements and formulas
- Wall: V = wall length × wall height × wall thickness
- Slab/plate: V = footprint × slab thickness
- Girder/beam: V = width × height × length (possibly as T- or rectangular section)
- Foundation: V = base area × depth (for stepped foundations, sum of partial bodies)
- Bored pile: V = π × (d²/4) × length
Reinforcement ratio and steel quantities
Without complete reinforcement drawings, the steel content is often estimated (e.g., in kg/m³ of reinforced concrete, depending on use and element category). From the concrete volume, the steel quantities for separation and sorting processes as well as for deploying concrete pulverizer and steel shear can be derived. For the workflow, it is decisive whether the concrete is first broken up with a concrete pulverizer and the steel is then separated with shears, or whether a combined approach is appropriate.
Quantity calculation in rock excavation and tunnel construction
In rock, including contexts such as rock demolition and tunnel construction, cubic capacities are determined from design and actual profiles. In tunnel advance and bench work, overbreak and fragment size distribution must be considered. For mechanical splitting with hydraulic wedge splitter, the length of split lines, number of drill holes, hole diameter, and lot sizes must be quantified.
Split lines, drilling patterns, and lot sizes
- Split length: Sum of the planned separation joints per advance or extraction face
- Number of drill holes: Split length divided by the spacing pattern (depending on rock strength)
- Lot size: Volume per work takt to coordinate with lifting devices and haulage logistics
The resulting quantities govern the need for hydraulic power, the number of splitting cycles, and the sizing of the stone splitting cylinders.
Relation to concrete pulverizer and hydraulic wedge splitter
Concrete pulverizer are designed for gripping, breaking, and reducing concrete members. Quantity calculation provides the required key data: element thicknesses, reinforcement ratios, break lengths, target particle sizes for onward loading. Hydraulic wedge splitter create defined separation joints in concrete or natural stone; decisive parameters are split lengths, number of drill holes, joint spacing, and the volume of the blocks to be separated. Both methods benefit from realistic volume and mass estimates, as these determine cycle times, gripping paths, intermediate storage, and means of transport.
Quantity calculation for gutting works and cutting
Before demolition, non-loadbearing layers, installations, and technical equipment are removed. Quantity allowances include areas for floor build-ups, linear meters of separation cuts, and counts of components. For precise openings, pre-cutting can reduce the load for concrete pulverizer. The total cutting meters serve to calculate equipment hours and consumables, as well as to coordinate with subsequent reduction works.
Reduction and separation processes: combination shears, multi cutters, steel shears, tank cutters
For metallic installations and structures, cutting lengths, material thicknesses, and cross-sections must be captured. From this, the need for cutting cycles and the suitability of tools is derived. In deconstruction projects using concrete pulverizer, the steel is often further separated with steel shear after breaking up. For tanks and vessels, circumference, wall thickness, and segmentation determine cutting quantities and the logistical sequence.
Key figures for estimating
- Total cutting length in m and average material thickness
- Counts of profiles/plates and their cross-sections
- Target particle sizes for the load (pre-sorting, recycling)
Hydraulic power packs: deriving power demand from quantities
Hydraulic power packs feed the cylinders, pulverizers, and shears. The quantity per unit time (e.g., m³/h of concrete reduction or m of split line/h) results from cycle time, stroke volume, operating pressure, and changeover times. From the planned daily quantity, the required operating time of the power pack is derived. Sizing of hydraulic power units is carried out so that sufficient flow is available for parallel consumers without causing unnecessary downtime.
Process planning and logistics based on quantities
The determined total quantity is divided into manageable lots. This allows equipment combinations—such as concrete pulverizer with hydraulic power pack and wheel loader—to be synchronized precisely. For splitting works, advance widths are chosen so that lifting devices and transport routes are not overloaded. From volume and density, the transport masses are obtained and thus the number and takt of haulage trips.
Disposal and material flow management
Separate collection of concrete, reinforcing steel, natural stone, and mixed fractions requires exact quantities. Quantity calculation serves as the basis for ordering containers, planning intermediate storage, and providing documentation to stakeholders. If in doubt, safety allowances for breakage losses and oversize are set low but traceably.
Capturing base data: measurement and modeling
Depending on data availability, record drawings, on-site measurement, trial exposures, and spatial models are combined. For elements without complete drawings, sections and grid measurements help determine thicknesses, layers, and cavities. On rock faces, geological banding and joints are documented to realistically plan splitability and the drilling pattern.
Quality assurance
- Plausibility checks by comparison with similar elements
- Spot measurements at critical locations
- Versioning of quantity states for estimating and billing
Safety and boundary conditions in quantity planning
Quantity allowances affect structural and operational safety. Lots that are too large can exceed gripping paths, stability, or lifting capacities. For splitting works, safety distances for uncontrolled fractures must be considered. References to standards and specifications must be checked on a project-specific basis; the values described here are of a general nature.
Typical mistakes and how to avoid them
- Openings and recesses not deducted: leads to overestimation of concrete quantity
- Reinforcement ratio assumed incorrectly: influences the choice of concrete pulverizer and shears
- Overbreak in rock ignored: underestimates haulage and sorting needs
- Logistics quantities not coordinated: downtime due to missing containers or transport
- Cycle times generalized: hydraulic bottlenecks with multiple consumers
Example calculations from practice
1) Slab deconstruction with concrete pulverizer: slab 25.0 m × 12.0 m × 0.22 m. V = 25.0 × 12.0 × 0.22 = 66.0 m³. Mass (2.45 t/m³) ≈ 161.7 t. Reinforcement ratio 90 kg/m³ → steel ≈ 5.9 t. Planning: lot size 6 m³ per takt → 11 takts. Transport: 12 t per trip → 14 trips for concrete, 1–2 trips for steel.
2) Wall opening with splitting device: wall 6.0 m × 0.35 m × 3.0 m, opening 2.0 m × 1.0 m × 0.35 m. V total = 6.0 × 3.0 × 0.35 = 6.30 m³. V opening = 2.0 × 1.0 × 0.35 = 0.70 m³. V net = 5.60 m³. Split line around the perimeter 6 m per opening, drilling pattern 25 cm → 24 drill holes. Cycle planning: derive splitting and lifting times per lot from experience values.
3) Rock removal in benches: area 18.0 m × 7.0 m, removal thickness 1.2 m. V = 151.2 m³. Density 2.70 t/m³ → 408 t. Overbreak allowance 8% → 438.6 t. Split-line spacing 0.6 m → 30 split lines at 7 m each = 210 m split length. Number of drill holes every 0.3 m → 700 drill holes. Determine hydraulic demand and power pack runtime from m of split line/h.
Checklist: step-by-step to reliable quantity calculation
- As-built capture: drawings, measurement, probes, material properties
- Model geometry: divide elements and rock volumes into partial bodies
- Calculate volumes: consider openings, cavities, and over/underbreak
- Determine material shares: reinforcing steel, inserts, installations
- Define lot sizes: suitable for concrete pulverizer, splitting cylinders, and logistics
- Match equipment performance and hydraulics: cycle times and parallel operation
- Derive disposal and transport quantities: containers, trips, intermediate storage
- Plausibilize and document: assumptions, sources, calculation steps
Documentation and post-calculation
Clear, traceable documentation of quantities, assumptions, and calculation paths facilitates site control and subsequent post-calculation. Deviations between allowance and actual quantities provide valuable key figures for future projects—such as realistic m³/h with concrete pulverizer for the respective element type or split meters/h in defined rock. This way, quantity calculations become more precise step by step, and workflows in concrete demolition, rock removal, gutting works, and natural stone extraction can be planned more efficiently.