Quantity calculation

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.

Accurate takeoffs stabilize cost forecasts, enable verifiable documentation for stakeholders, and support circular-economy goals by quantifying recyclable fractions from the outset. Consistent terminology and units across all parties reduce friction losses in planning and execution.

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.

Selection criteria for methods

• Data basis and accuracy class: record drawings vs. as-built survey vs. point cloud
• Complexity: simple solids vs. composite bodies with deductions and additions
• Time and cost: effort of capture and modeling compared with risk from uncertainty
• Traceability: reproducible calculation paths and auditable assumptions

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.

Practical conventions and allowances

• Rounding and significant digits: keep interim results with adequate precision, round final quantities only where contractually defined.
• Moisture influence: densities vary with moisture content; apply ranges and document chosen values.
• Bulking and swell: crushed concrete or rock can increase in volume by 10-30% compared with in-situ volumes.
• Deduction rules: define thresholds for deducting small openings, recesses, and embedded items consistently.
• Contingencies: add calibrated allowances for overbreak, uneven fracture edges, and screening losses, justified by experience or trial cuts.

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.

• Indicative ranges: slabs 60-90 kg/m³, walls 70-110 kg/m³, beams and girders 100-180 kg/m³, heavily reinforced or seismic zones potentially above 200 kg/m³.
• Local peaks: anchorage zones, column heads, and joints can exceed average ratios and affect tool choice and takt.

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

Discontinuities, weathering state, and uniaxial compressive strength influence spacing, hole diameter, and energy input. When the rock mass is anisotropic, pattern orientation is aligned with joint sets to optimize splitting efficiency and control fragment sizes.

Relation to concrete pulverizer and hydraulic wedge splitter

Concrete pulverizers 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 splitters 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.

• Key planning outputs: expected piece size distribution, cycle-time windows, hydraulic demand, and standby equipment for peak loads.

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.

Interfaces with structural deconstruction are defined clearly so that cutting, lifting, and reduction steps interlock without double handling or idle times.

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.

Rule-of-thumb conversions

• Flow: required l/min ≈ cylinder volume per stroke × strokes per minute (including return strokes).
• Power: kW ≈ (pressure in bar × flow in l/min) ÷ 600, plus efficiency and simultaneity factors.
• Cycle time: stroke time ≈ cylinder volume ÷ available flow, adjusted for throttling and load-dependent speed.

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.

Logistics and takt stabilization

• Dimension lots for continuous feeding of loading and haulage without bottlenecks.
• Provide buffers for breaks, changeovers, and inspection holds at defined takt positions.
• Align shift models and delivery windows with disposal site acceptance and access constraints.

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. Weighbridge reconciliation against planned masses improves forecasting accuracy for subsequent phases.

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.

Digital workflows and data sources

• Point clouds from laser scanning or photogrammetry for precise as-built geometry.
• Model federation from 2D plans and BIM to close gaps and derive takeoffs.
• Georeferencing to align measurements with transport routes and staging areas.

Quality assurance

• Plausibility checks by comparison with similar elements
• Spot measurements at critical locations
• Versioning of quantity states for estimating and billing
• Independent review of assumptions and unit conversions
• Change logs for traceable updates after site findings

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.

• Observe limits for vibration, noise, and dust; integrate suppression and monitoring quantities where required.
• Account for access, headroom, and bearing capacities in lot sizing and handling paths.
• Consider water ingress, ventilation needs, and lighting for underground or enclosed works.

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
• Overlapping geometries double-counted: inflated volumes and masses
• Unit mismatches and conversion errors: inconsistent bases between estimating and execution

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.

4) Natural stone block extraction: target block 2.2 m × 1.6 m × 1.4 m → V = 4.93 m³. Rock density 2.65 t/m³ → ≈ 13.1 t. Perimeter split length ≈ 2 × (2.2 + 1.6) = 7.6 m; bedding split 1.6 m. Total split length ≈ 9.2 m. Drilling pattern 0.25 m → ≈ 37 drill holes. Lot sizing aligned to lifting capacity and haul road gradients.

Checklist: step-by-step to reliable quantity calculation

1. As-built capture: drawings, measurement, probes, material properties
2. Model geometry: divide elements and rock volumes into partial bodies
3. Calculate volumes: consider openings, cavities, and over/underbreak
4. Determine material shares: reinforcing steel, inserts, installations
5. Define lot sizes: suitable for concrete pulverizer, splitting cylinders, and logistics
6. Match equipment performance and hydraulics: cycle times and parallel operation
7. Derive disposal and transport quantities: containers, trips, intermediate storage
8. Plausibilize and document: assumptions, sources, calculation steps
9. Set acceptance criteria: measurement methods and reporting cadence
10. Maintain a rolling forecast: update quantities with site findings and weighbridge data

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.

Operational KPIs for benchmarking

• Reduction performance in m³/h and t/h by element type and tool
• Split line productivity in m/h and drill holes/h
• Hydraulic energy per m³ reduced or per meter split
• Container turns and transport utilization per shift
• Share of recyclable fractions vs. mixed fractions by mass