The degree of compaction describes how densely a construction material or subsoil is packed compared to its technically achievable maximum. It influences the strength, stiffness, crack tendency, and fracture behavior of concrete, masonry, rock, and unbound layers. In concrete demolition and deconstruction, in strip-out and cutting, as well as in rock excavation, tunnel construction, and natural stone extraction, the degree of compaction directly affects the choice of approach and tools. In particular, the operating mode of hydraulic rock and concrete splitters, concrete pulverizers, and the associated reliable hydraulic power units depends on the fabric, porosity, and density of the structure to be separated.
Definition: What is meant by degree of compaction
The degree of compaction is the ratio of the actually achieved dry bulk density of a material to the maximum possible (reference) density under defined conditions, expressed as a percentage. For unbound construction materials (e.g., gravel, crushed stone, sand), a reference density from laboratory tests determined with standardized compaction energies is often used. In concrete, “compaction” describes the removal of air voids in fresh concrete and the optimization of particle packing; in the hardened state this appears as higher bulk density, lower capillary porosity, and improved durability. In natural and hard rock the term is used functionally: high packing density and low porosity mean, in practice, a tough, energy-absorbing fracture behavior, while loosely deposited or strongly jointed material splits or crushes more easily.
Practical relevance in demolition, deconstruction, and extraction
A high degree of compaction leads to increased compressive and splitting tensile strength in concrete and dense rock. This influences how forces must be introduced into the material. Stone and concrete splitters use controlled splitting pressure to initiate and steer cracks in a targeted manner—the more compact the fabric, the more carefully borehole spacing, wedge position, and activation sequence must be planned. Concrete pulverizers, in turn, benefit from existing weaknesses such as honeycombing or insufficiently compacted concrete; with very dense, highly compacted concrete, a pre-splitting with splitting cylinders is often appropriate before pulverizers reduce chunks to the required size. In strip-out and cutting, density affects cutting forces and tool wear; in rock excavation and tunnel construction, it determines whether low-vibration splitting methods are economical. In natural stone extraction, the degree of compaction, together with joint orientation and particle fabric, supports predictable block release.
Physical fundamentals: density, porosity, and fabric
A material’s response to compressive, tensile, and shear loading is determined by its internal structure. Relevant are:
- Bulk density and dry bulk density: Mass per volume, with or without moisture content—important for estimating self-weight and energy demand.
- Porosity and void content: Proportion of pores in total volume; controls water absorption, frost–de-icing salt resistance, crack propagation.
- Grain-size distribution and packing density: Well-graded aggregates achieve higher density for the same compaction energy.
- Fabric and texture: Orientation of grains, binder bridges, and microcracks steers crack propagation.
- Moisture content: Determines achievable density in soils; in concrete it influences fresh-concrete compaction and hydration.
For demolition this means: the denser and more homogeneous the material, the more clearly weakening lines must be created so that tools such as splitting cylinders and pulverizers work energy-efficiently.
Determination and evaluation of the degree of compaction
Unbound layers and subsoil
In road and civil engineering, the degree of compaction is often determined via a reference density from laboratory tests. On site, density determinations using extracted sample volumes, dynamic tests, or load plate tests are used to assess load-bearing capacity. A high degree reduces settlement risks beneath concrete slabs and foundations—relevant when separation cuts are planned in deconstruction and machine standing areas must be safely established.
Concrete (fresh and hardened)
In fresh concrete, vibration, rodding, or internal vibrators remove air. In the hardened state, bulk density, ultrasonic pulse velocity, core drilling evaluation, and rebound values provide indications of compaction quality. Visible honeycombing, gravel pockets, or pronounced porosity indicate a low degree of compaction and locally reduced strength—starting points for the use of concrete pulverizers.
Rock and natural stone
Rock has no “compaction” in the classical sense, yet porosity, fabric, and joint spacing play a similar role. Dense, fine-grained rock (e.g., basalt, granite) requires higher line loads and tighter borehole spacing for splitting than porous, jointed sandstone or limestone.
Influence on the selection and application of tools
The degree of compaction serves as a guiding parameter for the combination and sequence of equipment in demolition and extraction:
- Stone and concrete splitters / rock wedge splitters: In dense concrete or compact rock, first create targeted weakening along rows of boreholes; adapt spacing and penetration depth to density and fabric.
- Concrete pulverizers: Efficient for downsizing to transport or sorting size after pre-splitting or in low-compacted material.
- Combination shears and multi cutters: For composite elements with varying densities (concrete with reinforcement, masonry) to enable selective separation in strip-out and special demolition.
- Steel shears and tank cutters: For purely metallic components the degree of compaction is irrelevant; material condition, wall thickness, and cut line are decisive.
- Hydraulic power packs: Pressure and flow must match tool cut-out and the material resistance; dense concrete or rock requires consistent energy supply throughout the entire splitting sequence.
Planning steps: from findings to execution
- Investigation: Visual inspection for porosity, honeycombing, cracks, fabric; include samples and parameters from drawings and project documents.
- Assessment: Estimate degree of compaction or bulk density; consider moisture and temperature.
- Strategy: For a high degree of compaction, pre-splitting with stone and concrete splitters, then downsizing with concrete pulverizers; with low-compacted material, direct pulverizer work may be feasible.
- Crack steering: Define borehole spacing, edge distance, and sequence to steer cracks predictably and avoid spalling.
- Energy supply: Size hydraulic power packs to tool specifications and material resistance.
- Control: Create a trial area, fine-tune parameters, document settings.
Material behavior: examples from application areas
Concrete demolition and special demolition
Highly compacted concrete with low porosity shows brittle but energy-intensive fracture behavior. A sequential splitting strategy with tighter borehole grids is sensible. After pre-splitting, concrete pulverizers reduce block size. In insufficiently compacted zones, direct pulverizer work is often possible because local weaknesses reduce force demand.
Strip-out and cutting
With sawing and cutting, cutting force and tool stress increase with density. Pre-drilling or wedges can reduce peak loads and relieve kerfs. In composite zones, a coordinated sequence of splitting and pulverizer work supports selective separation.
Rock excavation and tunnel construction
In compact, slightly jointed rock, tight splitting spacing and controlled sequences are crucial to create designed contours with low vibration. In more jointed, porous rock, spacing can be larger; crack propagation more often follows the natural joint structure.
Natural stone extraction
For block release, joint systems and density-dependent splitability are utilized. The denser the stone, the more precisely splitting pressure, equipment sequence, and the geometry of borehole rows must be tuned to achieve smooth fracture surfaces.
Indicators and effects of different degrees of compaction
- Low degree of compaction (concrete): Visible voids, honeycombing, rough fabric; easier bite-in for concrete pulverizers, reduced compressive strength, potentially higher water uptake.
- High degree of compaction (concrete): Dense, homogeneous matrix; higher force demand, sensible pre-splitting with stone and concrete splitters or rock wedge splitters.
- Loosely deposited subsoil: Settlement risk when setting up equipment; secure standing areas.
- Compact rock: Tough splitting behavior; finer grids and precise sequences necessary.
Typical planning errors and how to avoid them
- Underestimating density: Leads to excessive borehole spacing and uncontrolled cracking. Better: trial area and adjustment of grids.
- Insufficient relief cuts: Edge spalling occurs in highly compacted concrete. Better: define weakening lines in advance.
- Wrong tool sequence: Direct pulverizer work in very dense material increases tool wear. Better: pre-splitting followed by downsizing.
- Ignored moisture: Moist, dense concrete damps crack propagation. Better: adjust parameters and extend the sequence.
Safety and boundary conditions
Work steps must be planned to avoid uncontrolled fractures. Standing areas must be load-bearing and level; especially on loose subgrade, additional measures for setting up hydraulic power packs and equipment are required. The higher the degree of compaction, the greater the stored stresses may be—dimension safety distances and protection against spalling accordingly. Notes are general and do not replace an object-specific assessment.
Parameters that influence the degree of compaction in practice
- Aggregate composition: Well-graded aggregates increase achievable density.
- Compaction energy: Intensity and duration of compaction determine proximity to the maximum density.
- Moisture content: An optimum exists in soils; too dry or too wet reduces attainable density.
- Water–binder ratio (concrete): Low values reduce capillary pores; adequate concrete curing is required.
- Fabric ageing: Hydration progress and drying influence bulk density and crack tendency.
Documentation and quality assurance
For predictable results, document initial conditions (visual findings, samples), selected parameters (borehole spacing, splitting sequence, pressure levels), the hydraulic power packs used, and the findings from trial areas. This way, settings for stone and concrete splitters and concrete pulverizers can be transferred to similar materials and effort reduced on the next project.