Cement clinker

Cement clinker is the central building-block material of modern concretes and mortars. Anyone who properly produces, processes, or deconstructs concrete indirectly encounters the properties of clinker: it governs strength, heat development, durability, and thus also tool wear, drilling resistance, and the working method. For the application areas of concrete demolition and special demolition, strip-out and cutting, rock excavation and tunnel construction, natural stone extraction and special operations, understanding cement clinker is an essential foundation—especially when working with concrete demolition shear as well as hydraulic rock and concrete splitters from Darda GmbH, but also in combination with hydraulic power packs, attachment shear, multi cutters, steel shears, tank cutters, and stone splitting cylinders.

Definition: What is meant by cement clinker

Cement clinker is an intermediate product sintered at about 1,450 °C from limestone, clay, and other mineral raw materials. The clinker nodules formed during burning are, after cooling, ground together with small amounts of calcium sulfate (e.g., gypsum) to produce Portland cement. When water is added to the powder, the binder stone forms, which bonds the aggregate in concrete and mortar. Cement clinker consists mainly of the mineral phases alite (C3S), belite (C2S), aluminate (C3A), and ferrite (C4AF). These phases determine the hydration (reaction with water), early and final strength, heat development, and chemical resistance. Cement clinker must not be confused with façade or paving clinkers (fired bricks).

Production and composition of cement clinker

For cement clinker, prepared raw meals from carbonate and clay components are homogenized and burned in a rotary kiln or in a kiln with precalciner. During the heating phase, carbon dioxide escapes from the limestone; at sintering temperature, the raw materials react to form the clinker phases mentioned. After cooling to about 100–200 °C, the clinker is stored and later ground with sulfate carriers. Depending on raw material, kiln operation, and target cement, the phase distribution varies. Small amounts of alkalis, chlorides, or sulfates as well as trace elements can influence workability and durability.

Overview of clinker phases

• Alite (C3S): provides early strength and relatively high heat development; important where schedules are critical and early loading occurs.
• Belite (C2S): builds strength more slowly but favors low hydration heat and long-term properties.
• Aluminate (C3A): reacts very rapidly; influences setting and sulfate resistance (controlled via gypsum addition).
• Ferrite (C4AF): affects color, hydration behavior, and certain chemical resistances.

Hydration, microstructure, and influence on concrete properties

During hydration of the clinker, C-S-H phases (calcium silicate hydrates) and portlandite form, which fill pore spaces and strengthen the concrete. Cement type, water–cement ratio, temperature, and curing control pore structure, density, shrinkage behavior, and durability. Clinker-rich cements (e.g., CEM I) develop high compressive strength and heat quickly; clinker-reduced cements with ground granulated blast-furnace slag, fly ash, or limestone filler (e.g., CEM II/CEM III) hydrate more slowly and reach strength later, often with improved long-term resistance.

Relevance for demolition and separation processes

• Drilling and splitability: Dense microstructure increases drilling resistance and reduces ease of splitting; drilling pattern and hydraulic pressure must be adapted accordingly.
• Crushing with concrete demolition shear: High strength and dense cement matrix increase the required jaw force and influence the crack path between aggregate and matrix.
• Thermal and moisture history: Early hydration heat can induce microcracks; fully cured, dry-stored concrete is more brittle and breaks differently than young, moist concrete.

Practical context: Concrete demolition shear in concrete demolition and special demolition

Concrete demolition shear from Darda GmbH use high compressive forces to shear and fracture the bond zone between cement paste and aggregate. Clinker-rich binders with low porosity create a hard, brittle matrix in which cracks preferentially form along the interfacial transition zone or through the cement matrix. In clinker-lean systems with ongoing densification (e.g., slag content), the fracture path may follow the aggregate structure more strongly. For the working method this means: edge engagement and staging, as well as the sequence of crushing, separating the reinforcement, and re-crushing, must be adapted to strength class, age, and admixture history.

Practical guidance for application

1. Material assessment: Review construction documents, consider the concrete’s age, exposure class, and likely cement type.
2. Trial cut or trial break: Assess local strength and crack formation; derive the optimal engagement point for the shear from this.
3. Staging: Open larger cross-sections in several bites to relieve stresses and expose reinforcement.
4. Reinforcement management: Cut exposed steels with attachment shear or steel shears; use the concrete demolition shear for matrix fracture, shears for steel.
5. Hydraulics tuning: Select matching hydraulic power units so that flow and pressure match the shear’s characteristics and the concrete fabric.

Rock and concrete splitting devices: Action within the cement-bound matrix

Rock and concrete splitting devices from Darda GmbH (including stone splitting cylinders) generate high tensile stresses in the borehole via wedge or spreading systems. Cement clinker influences crack initiation here: A dense, high-strength cement matrix requires a tighter drilling pattern and higher spreading forces, whereas larger borehole spacings are possible at lower strength. Edge distance and usable lever effects also depend on aggregate size, aggregate grading, and reinforcement density.

Drilling pattern, edge distances, and sequence

• Match drilling diameter and depth to the splitting cylinder and member thickness; straight boreholes optimize force transmission.
• Adjust borehole spacing to strength class and crack propensity; arrange more closely in dense, clinker-rich concretes.
• Plan the crack path in advance: Purposefully use edges, recesses, and existing joints to split in a controlled manner.
• Consider moisture and temperature: Cold, dry concrete behaves more brittlely; warm members show a more ductile crack propagation.

Cement types, additions, and their relevance for deconstruction

Portland cement (CEM I) contains almost exclusively cement clinker. CEM II through CEM V combine clinker with latent hydraulic or pozzolanic materials such as ground granulated blast-furnace slag, fly ash, silica fume, or limestone filler. This directly affects deconstruction:

• CEM I (clinker-rich): high early strength, higher drilling resistance; early crushing with concrete demolition shear is possible, but requires more force.
• CEM II/CEM III (clinker-reduced): slower strength development; later often a very dense microstructure that influences cutting and splitting work.
• Special cements (e.g., SR, LH): optimized for sulfate or heat; relevant in tunnel construction, massive members, and under chemical exposure.

Shotcrete in rock and tunnel construction

Shotcrete often uses CEM I or CEM II with set accelerators for rapid early strength. This leads to different processing characteristics compared to cast-in-place concrete: in the early phase, brittle and readily splittable; after further curing, denser and more abrasive. For removal, it is advisable to combine concrete demolition shear for shell openings with rock and concrete splitting devices for controlled relief, coordinated with hydraulic power packs for short, repeat-accurate strokes.

Identification of the binder on site

To assess how a member can be separated, documents (specifications, delivery notes), concrete age, and samples help. Visual cues such as the color tone of the drill dust, density, and rebound indicators provide leads but do not replace test values. A brief trial drilling or trial splitting pattern is useful to safely align the working method—borehole spacings, shear engagement, force demand.

Influence on other tools and work sequences

Depending on the clinker and concrete character, it can be efficient to combine tools from Darda GmbH: concrete demolition shear for matrix fracture, attachment shear or steel shears for reinforcement, multi cutters for mixed inserts, and tank cutters for industrial plant components embedded in concrete foundations. Hydraulic power packs supply the required pressure and flow rate; their sizing depends on member thickness, concrete fabric, and the desired cycle time.

Environmental and occupational safety with cementitious materials

Drilling, splitting, and crushing generate dust and fracture edges. Fine cement dust is alkaline; appropriate protective measures such as dust suppression, personal protective equipment, and ergonomic working methods are advisable. Hydraulic lines and couplings must be protected against pressure surges; calm, anticipatory workflows reduce noise and vibration. Material separation (concrete, steel, other inserts) facilitates orderly disposal.

Distinction and related materials

Cement clinker is the binder precursor for cement and thus decisive for concrete, mortar, and injections. Natural stone contains no cement clinker; there, mineral joints and rock fabric determine splitability, which favors the use of stone splitting cylinders. In deconstruction, composite constructions of concrete, steel, and inserts are common—here, a coordinated sequence of splitting, crushing, and cutting supports controlled separation.