The melting point describes the temperature at which a solid transitions into the liquid state. In the context of concrete demolition, special demolition, rock excavation, tunnel construction as well as building gutting and cutting, this term has particular significance: it helps classify materials, processes, and risks—especially when comparing thermal methods with mechanical, cold-working applications using tools such as concrete pulverizers or hydraulic rock and concrete splitters by Darda GmbH. Whereas thermal methods heat material up into the melting range, hydraulic cutting and splitting processes rely on pressure and shear rather than heat—with clear effects on operational safety, structural element behavior, and tool wear.
Definition: What is meant by melting point
The melting point is the temperature at which a crystalline solid, at a defined pressure (usually 1 bar), is in equilibrium with the liquid phase. Upon reaching this melting temperature, latent heat (heat of fusion) is absorbed without the temperature rising further during the phase transition. Pure metals have a sharply defined melting point; alloys often show a melting range. Amorphous substances such as glass, bitumen, or many plastics do not have a distinct melting point but exhibit softening or glass transition ranges. For rocks and concrete, a clear melting point is likewise not given, as these are multi-component and composite systems with different thermal decomposition steps.
Physical fundamentals and influencing factors
The melting point depends on several factors. Pressure usually changes it only moderately (at the pressures relevant here), impurities and alloying elements often lower it (eutectic), and the microstructure (grain size, precipitates, pre-treatment) influences transition ranges. Thermal conductivity, heat capacity, and thermal expansion determine how quickly a component is locally heated and whether thermal stresses arise. In the practice of demolition and deconstruction, process heat mainly results from friction at cutting edges, pressing faces, and reinforcing steel contact surfaces as well as from energy conversion in the hydraulic system—well below melting temperatures, but relevant with respect to tempering colors, loss of hardness, and wear in tool steels.
Significance of the melting point in concrete demolition and special demolition
In concrete demolition, concrete and rock are typically broken brittle and not melted. Here, the melting point serves more as a reference parameter to assess thermal risks and material behavior: reinforcing steel has melting temperatures far above what mechanical methods can reach. If high friction is nevertheless involved, local heating can affect tool cutting or jaw zones. Mechanical methods with concrete pulverizers and hydraulic splitters act purposefully without significant heat input, minimizing thermal microstructural changes in the component and sparks—an advantage for safety, especially in special operation and on contaminated structures.
Concrete pulverizers: controlled separation without melting
Concrete pulverizers generate high compressive and shear forces to crush concrete and cut reinforcing steel. The material remains in the solid state; the phase transition does not act as the operating principle but only as a safety and material limit. The key is limiting frictional heat so that the cutting-edge hardness is maintained and no tempering zones form.
Hydraulic splitters: brittle fracturing instead of thermal separation
Hydraulic splitters use controlled tensile and compressive stresses to initiate and propagate cracks. The melting point of the mineral phases is theoretically present but practically irrelevant here, because the process operates far from thermal methods. More relevant are crack propagation, notch effect, and the stress state within the material.
Material properties: steel, concrete, and rock compared
For planning and evaluating separation strategies, it is helpful to know typical temperature ranges:
- Unalloyed and low-alloy steels: approx. 1425–1540°C (melting point, depending on carbon content and alloying)
- Cast iron: approx. 1150–1200°C
- Aluminum (alloys): approx. 600–660°C
- Copper: approx. 1085°C
- Rocks: no single value; melting of mineral mixtures mostly >1000°C, depending on composition and pressure
- Concrete: no defined melting point; thermal decomposition of the cement matrix begins, depending on moisture content and binder, from approx. 200–300°C, with dehydration and matrix degradation up to above 600–800°C
In practice, these temperatures are not reached with mechanical cutting and splitting processes. Nevertheless, lower temperature rises can cause local microstructural changes at tool edges if grinding or cutting is performed with unsuitable cooling.
Process heat, friction, and tool wear
Even without melting, temperature is a major influence. Short-term spikes can lead to loss of hardness in tool steels, while long duty cycles promote wear mechanisms such as adhesion, abrasion, and micro-chipping. Good heat dissipation via massive jaws, suitable cutting-edge geometries, and well-maintained bearings reduces frictional heat. The goal is to stay well below tempering temperatures and avoid thermally induced microstructural transformations.
Hydraulic power packs: temperature control in the system
Hydraulic power packs convert power into pressure; as with hydraulic power units, waste heat is generated in the oil circuit. While this system heat is separate from the melting point of the materials being processed, it does affect viscosity, seals, and the thermal load on adjacent assemblies. A stable thermal balance increases the reproducibility of separation forces and limits unnecessary frictional work at tool contacts.
Steel shears, Multi Cutters, and tank cutters: thermal aspects
With steel shears and Multi Cutters, frictional heat at the cutting edges is unavoidable but controllable. In special operation scenarios—for example, when working on tanks and pipelines—avoiding sparks and local overheating plays a special role. Here, knowledge of melting and ignition temperatures of relevant substances is important to minimize risks from ignition sources, outgassing, or hot particles.
Measurement and test methods for the melting point
Different methods are used to determine melting points depending on the material. For metals, pyrometric and thermal analytical methods are used; for organic substances and bitumen, capillary, crucible, and dynamic methods such as Differential Scanning Calorimetry are employed. For concrete and rock, melting point measurements are uncommon; here, thermogravimetric analyses, dilatometry, and high-temperature exposure tests are used to capture decomposition behavior, moisture release, and dimensional changes.
Influence of pressure, moisture, and environment
Increasing pressure slightly raises the melting point for many crystalline substances. Foreign substances and dissolved components often lower it by disturbing the crystal lattice. Moisture affects composite construction material such as concrete not via the melting point but via evaporation, pore pressure, and thermal shock: with rapid heating, water vapor can lead to microcracks—an important aspect when deconstructing heat-damaged structural elements.
Distinction: softening, glass transition, and thermal decomposition
Melting is a phase transition with latent heat. In contrast are the softening of amorphous materials (e.g., bitumen, plastics), the glass transition in polymeric or glassy materials, and the thermal decomposition of composite materials. In building gutting and when cutting fit-out materials, this distinction is relevant: adhesives, sealants, or cable jacketing show no clear melting point but are sensitive to temperature increases—which affects emission and particle behavior.
Practice-oriented guidance for use
The following notes support temperature-aware work in concrete demolition, in natural stone extraction, in tunnel construction, and in special demolition:
- Prefer mechanical, cold-working methods with concrete pulverizers or hydraulic splitters when component or environmental conditions suggest thermal risks.
- Regularly inspect cutting contours and jaw surfaces; tempering colors, burr formation, or discoloration indicate local overheating.
- Monitor hydraulic oil temperature and balance load peaks through work rhythm, pauses, and matching power unit sizes.
- Ensure cooling when grinding and honing cutting edges to avoid loss of hardness by exceeding tempering temperatures.
- Separate metals with a low melting point (e.g., aluminum) in a material-appropriate manner; limit friction and cold welding through suitable geometries.
- In special operation environments (e.g., tanks, pipelines), minimize sparks and heat input; be mindful of possible residual contents and ignition sources.
Maintenance and service life: relation to the melting point
Even if the melting point is rarely reached in operation, temperature control determines service life and functional reliability. Overheated cutting edges can partially lose their martensitic structure, seals age faster at elevated system temperature, and microstructural crack nuclei preferentially form in thermally damaged edge zones. Proper maintenance preserves the hardness and toughness of the tools and ensures that separation forces act reproducibly—without unwanted thermal side effects.
Application examples from practice
During the deconstruction of a reinforced concrete beam, a concrete pulverizer separates the reinforcing steel purely mechanically. The melting point of the steel remains far away as a theoretical limit; practically relevant are avoiding tempering colors on the cutting edges and limiting frictional heat.
In natural stone extraction, a hydraulic splitter splits massive blocks along existing planes of weakness. The mineral phases with high melting temperatures play no direct role; decisive are the stress state, crack propagation, and uniform load application.
In a special operation on tanks, a tank cutter supports safe opening without bringing material into the melting range. The absence of significant heat sources reduces the risk of thermally affecting residual contents or reaching flammable atmospheres.