Creep behavior

Creep behavior—the time-dependent deformation of materials under constant load—is a central topic in deconstruction, demolition, and rock cutting/processing. It influences how structural elements and rock masses change after forces are applied, how cracks grow, and how cut or split gaps remain open. For practical work with Darda GmbH equipment—such as concrete pulverizers, hydraulic rock and concrete splitters, rock splitting cylinders, steel shears, Multi Cutters, combination shears, tank cutters, and the associated portable hydraulic power units—creep behavior determines the optimal force dosing, holding times, re-press cycles, and safety measures in application areas such as concrete demolition and special demolition, building gutting and cutting, rock breakout and tunnel construction, natural stone extraction, and special applications.

Definition: What is meant by creep behavior

Creep behavior is the time-dependent, permanent deformation of a material under constant stress. Unlike the immediate elastic strain, creep strain develops over minutes, hours, or months. Concrete, many rocks, and polymers exhibit pronounced creep at room temperature; metals creep primarily at elevated temperatures. Creep must be distinguished from shrinkage (moisture-, chemical-, or temperature-induced volume change without external load) and from stress relaxation (load decrease at constant strain). In demolition and cutting/separation technology this is relevant because time-dependent deformations influence crack guidance, the opening of gaps, and the settling of members—with direct implications for the use of concrete pulverizers and rock and concrete splitters.

Materials science: Creep in concrete, steel, and rock

The causes and manifestations of creep differ by material.

Creep in concrete

Concrete behaves viscoelastic to viscoplastic: Under sustained compressive or tensile stress the cement paste matrix flows microscopically; there is microcreep in gel and interfacial transition zones as well as time-dependent rearrangement within the aggregate. Influences include the water-cement ratio, moisture content (drying vs. basic creep), the age of the concrete, temperature, and the stress level relative to strength. For practice this means: A crack initiated by concrete pulverizers can continue to open after the jaws are released or partially close; a gap produced with rock and concrete splitters can enlarge over time as compressive and interfacial forces continue to act.

Creep in rock

Many rocks (shales, clays, rock salt, and certain granites) show measurable time-dependent deformation under sustained load. Mechanisms include grain boundary sliding, microcrack growth, and—under high confinement—subcritical crack growth. In rock breakout and tunnel construction this leads to time-dependent gap formation and, in narrow openings, possibly to creep closure. In natural stone extraction, creep can facilitate planned separation along bedding or joint planes—provided holding times and press sequences are tuned to the material behavior.

Creep in metals

At ordinary ambient temperatures steels creep only slightly. More relevant for steel shears, Multi Cutters, combination shears, and tank cutters is springback (elastic recovery) immediately after the cut as well as the release of existing residual stresses. Time-dependent deformations can occur indirectly when clamping situations change after load redistributions.

Influencing factors on creep behavior

• Stress level: The higher the stress relative to strength, the greater the creep rate; near compressive or tensile strength, tertiary creep with rapid failure may occur.
• Time and load duration: Primary creep (decreasing rate), secondary creep (approximately steady-state), and tertiary creep (accelerated).
• Temperature: Increases the tendency to creep in concrete and rock; relevant during summer heating, in tunnels, or after fire.
• Moisture: Drying promotes creep in concrete (drying creep); moisture content and environmental changes are decisive.
• Material parameters: Water-cement ratio, aggregate, porosity, age of concrete, layering/anisotropy of rock.
• Geometry and boundary conditions: Slender members, notches, borehole spacing, support, restraint, and fixity strongly influence creep.
• Reinforcement: Reinforcement, inlays, or existing steel sections limit strains but shift stresses over time.

Why creep affects deconstruction and cutting/separation technology

In applications with concrete pulverizers and rock and concrete splitters, creep directly affects crack initiation, crack propagation, and gap opening. Time-dependent redistributions can after a loading phase lead to settling of members or additional crack opening—or partially close a cut gap and thus promote jamming. For hydraulic power packs this means holding functions, re-pressing, and controlled release play an important role.

• Concrete pulverizers: Re-pressing may be necessary to achieve a targeted gap width; releasing too early can produce springback and local closing movements.
• Rock and concrete splitters: Pressure holding times foster the development of continuous cracks between boreholes; creep can stabilize the desired crack network.
• Rock breakout and tunnel construction: Creep closure of narrowly supported openings is possible; controlled press sequences and temporal staggering reduce risks.
• Building gutting and cutting: When separating composite sections (concrete with steel), time-dependent redistributions change the tendency of remaining sections to jam.

Equipment and system perspective: hydraulics, forces, holding times

Hydraulic power packs and tools from Darda GmbH act within a system based on force, displacement, and time. Creep behavior determines how long pressure should be held or how a jaw position should be fixed in order to stabilize the crack and avoid unwanted movement.

Concrete pulverizers: crack control through load duration

In tong-based separation processes, tensile and shear stresses arise that initiate cracks. A short holding time promotes controlled opening; a longer holding time can—depending on moisture and age of the concrete—produce additional creep strain and drive the crack further. In reinforced members, time-dependent load redistribution between concrete and steel should be expected.

Rock and concrete splitters: plan press cycles

When splitting via boreholes, splitting tensile stresses are introduced. Multiple press cycles with short relief phases allow the material to redistribute stresses via creep and microcracking. In this way, continuous cracks between the boreholes can be produced without losing control of the member.

Rock breakout and tunnel construction: use and control time-dependent behavior

In rock masses, creep leads to gradual deformation and can produce opening or closing movements in the area of anchor points, supports, and tunnel contours. For the use of rock splitting cylinders, a time-staggered pressure approach is recommended that exploits natural crack propagation along weakness zones. At the same time, safeguards against creep closure (wedges, shims, temporary supports) should be provided.

Natural stone extraction: block separation, bedding, annual cycle

In natural stone extraction, the rock-dependent creep behavior can improve separation quality when drilling pattern, press pressure, and holding time are tuned to joint systems and stratification. Temperature and moisture fluctuations between times of day influence the creep rate; steady holding phases after the first press impulse favor a clean crack opening.

Building gutting and cutting: metallic components and composite action

With steel shears, Multi Cutters, combination shears, and tank cutters, the focus is less on material creep and more on the time-dependent relaxation of composite sections. After the cut, members can move by springback; existing residual stresses in plates and sections are redistributed. In composite slabs or reinforced concrete members these effects superimpose with the creep of concrete—with consequences for holding and safeguarding measures.

Measurement, prediction, and assessment

In project practice, creep effects are accounted for via experience, material parameters (e.g., creep coefficient in concrete), and on-site observation. For deployment planning with Darda GmbH equipment, the following steps have proven effective:

1. Preliminary investigation: material type (concrete age, moisture, rock type), geometry, restraints, reinforcement.
2. Define load level: choose target forces so that primary creep is usable while avoiding tertiary creep.
3. Set holding times: time windows in which pressure is maintained or jaws remain closed.
4. Monitoring: markings, gauge wedges, or gap gauges to observe crack opening and settling.
5. Re-press strategy: cycles that promote crack advance without triggering uncontrolled breaks.

Practical guide: procedure on site

1. Create a cutting and splitting concept: define drilling pattern, engagement points for concrete pulverizers, shoring, and catch measures.
2. Plan press and holding phases: align pressure level and duration with the material and member; allow short reliefs for stress redistribution.
3. Protection against jamming: use wedges, shims, and temporary spacers to prevent closing movements due to creep.
4. Sequencing: separate sections so that load paths are maintained; if necessary, pre-relieve with rock splitting cylinders.
5. Controlled release: after separation, reduce jaw/pressure slowly to avoid abrupt movements due to springback.
6. Follow-up: check gap width, reset wedges, and secure members before the next cut or press operation.

Safety and quality in dealing with time-dependent deformations

• Keep hazard area clear: Creep and springback movements occur with delay; maintain person stand-off distances and exclusion zones.
• Secure members: Shore, prop, suspend; no load changes without safeguards.
• Stepwise pressure change: Avoid sudden unloading; controlled pressure reduction decreases unpredictable movements.
• Documentation: Record observations on gap openings, holding times, temperature, and moisture—valuable for fine-tuning subsequent work steps.

Distinction from shrinkage, relaxation, and springback

Creep is the increase in deformation at constant stress. Shrinkage causes deformation without external load (e.g., moisture loss) but can generate stresses. Relaxation is the decrease in stress at constant strain—typical in tensioned elements or with fixed jaw position. Springback is an immediate elastic partial recovery after unloading and must always be factored into cutting and tong operations.

Application in the deployment areas of Darda GmbH

In concrete demolition and special demolition, building gutting and cutting, rock breakout and tunnel construction, natural stone extraction, and special applications, understanding creep behavior is a prerequisite for predictable, safe workflows. Concrete pulverizers benefit from deliberately chosen holding times for crack stabilization; rock and concrete splitters and rock splitting cylinders use press cycles to form defined separation planes; steel shears, Multi Cutters, combination shears, and tank cutters require particular attention to springback and load redistributions, which can have time-dependent effects.