Cem i

CEM I cement is the designation for pure Portland cement and thus a cornerstone of modern concretes. Its composition, hydration, and strength development shape both the design and execution of concrete structures—and, later in the service life, concrete demolition and special demolition. For users working with concrete pulverizers or concrete splitters, understanding CEM I provides concrete guidance on splitting behavior, cutting forces, and the optimal timing for using hydraulics in building gutting and concrete cutting, in special demolition, and in selective deconstruction. For reference on methods and sequences, see concrete demolition and special deconstruction.

Definition: What is meant by CEM I

Under European cement standards, CEM I is the Portland cement with a clinker content of typically 95–100 mass percent, complemented by up to 5 percent minor constituents. The mineralogical main phases of Portland cement clinker (alite, belite, aluminate, ferrite) react with water (hydration) to form C‑S‑H phases and portlandite. This results in the characteristic compressive strength, stiffness, and the structure of the concrete. CEM I is classified into strength classes 32.5 / 42.5 / 52.5, with normal (N) or rapid early strength (R). These classifications describe the compressive strength after 28 days and the early strength, which are relevant for on‑site workflows and demolition project planning.

Material properties and structure of CEM I

The hydration of CEM I produces a fine‑pored cement paste microstructure of C‑S‑H phases that holds the concrete structure together and encases the aggregates. Fresh and young concretes show different mechanical behavior than aged components due to heat of hydration, shrinkage, and creep. With increasing age, carbonation, moisture cycles, and possible freeze‑thaw exposure lead to changes in stiffness and fracture energy. For interventions with concrete pulverizers as well as concrete splitters, this means: crack initiation and propagation depend strongly on pore structure, moisture content, and strength class; dry, highly carbonated CEM‑I concretes can often be split more brittlely than young, still moist concretes of the same strength.

Influence of CEM I on demolition and splitting techniques

The binder type shapes fracture behavior under compressive, tensile, and shear loading. At equal compressive strength, CEM‑I concretes often exhibit lower fracture strain and higher brittleness than concretes with latent hydraulic or pozzolanic additions. In the practice of concrete demolition and special demolition, this has several consequences:

• Splitting behavior: In CEM‑I‑rich, dense concretes, splitting and splitting tensile strength are correlated; concrete splitters can deliberately initiate cracks along weaker zones (construction joints, notches, borehole axes).
• Cutting and biting: concrete pulverizers offer advantages when the matrix fractures in a brittle manner and aggregates are well bonded; with very tough behavior, higher jaw forces and the coordinated use of a matched hydraulic power unit are relevant.
• Equipment combinations: Pre‑drilling and splitting can reduce the cross‑section before combination shears, Multi Cutters, or steel shear separate the reinforcement; this lowers peak loads and reduces the risk of uncontrolled fracture patterns.
• Temperature and moisture effects: Warm, dry CEM‑I concrete components respond more brittlely; in cooler, moist environments, the energy to failure increases. This influences the choice between splitting, biting, or cutting in building gutting and concrete cutting.

Strength classes, early strength, and time windows in deconstruction

The classes 32.5 / 42.5 / 52.5 and the N/R suffixes describe the level and rate of strength development. For interventions with concrete pulverizers or concrete splitters, practical guidelines emerge:

• Young component (CEM I 42.5 R, early days): Still hydrating, higher ductility, lower final strength. Cutting and splitting forces are moderate, but springback is possible. Careful shoring is essential.
• In service (CEM I 32.5 N to 52.5 N, ≥28 days): Final strength reached, structure stable. Brittle fracture more likely, predictable crack patterns—advantageous for a splitting strategy with rows of boreholes.
• Old concrete (decades, carbonated): Near‑surface densification, reduced pH, possible microcracks. Often efficient biting with concrete pulverizers at edges and bearing zones, combined with controlled splitting.

Interaction with reinforcement: Cutting, exposing, sequences

In CEM‑I concrete, the bond between cement paste and steel is essential for force transfer. In deconstruction, carbonation and moisture states lead to variable bond strength. Proven procedures tailored to a CEM I matrix:

• Sequential approach: First weaken the cross‑section using concrete splitters, then cut the reinforcement with steel shear or Multi Cutters.
• Local exposure: Use concrete pulverizers to bite away concrete to access reinforcement; in a dense matrix, pre‑splitting helps to facilitate removal.
• Special cases: Thick, high‑strength CEM‑I sections often require higher splitting pressures; an appropriately sized hydraulic power pack ensures consistent performance. For tanks and shells, depending on the material, tank cutters may also be considered.

Identification and documentation of CEM I in existing structures

Ideally, secure assignment of the binder is achieved via existing documentation. If these are unavailable, indicators and tests help and can be taken into account in planning for concrete demolition and special demolition:

• Documents and delivery notes: Information on cement type and strength class provides the most reliable indications.
• Core samples and laboratory: Petrography and binder analysis can distinguish CEM I from blended cements using concrete cores.
• Component indicators: High early strength and dense cement paste commonly point to CEM I; however, this is not proof and does not replace testing.

Planning relevance

Knowing the cement type supports the selection of splitting and cutting parameters, the positioning of rows of boreholes, and the estimation of fracture patterns. This allows work steps in building gutting and concrete cutting and in special demolition to be structured efficiently and safely.

Weathering, aging, and damage in CEM I concrete

Moisture, temperature, and chemical exposure change the properties of CEM‑I concrete over its service life. Relevant for the practice with concrete pulverizers and concrete splitters:

1. Carbonation: Increases near‑surface hardness but can lead to microcracks. Cracks steer the splitting front—beneficial for controlled separation.
2. Freeze‑thaw: Local loosening of the structure in edge zones; biting at edges is facilitated while the core remains resistant.
3. Chemical attack: Sulfate or acid exposure reduces matrix strength; load‑bearing capacity assessment and safeguarding measures must be adjusted accordingly.

Moisture balance

A high moisture content increases fracture energy and can raise the energy required for splitting or biting. Dry edge zones are often easier to open, which influences the sequence strategy.

Recycling and material flow management for CEM I concrete

The deconstruction of CEM‑I‑containing components enables high‑quality circular use. Selective removal with concrete pulverizers and targeted splitting of large volumes facilitate separation of concrete and reinforcement. Downstream crushing and screening stages yield recycled aggregates that—depending on quality and the normative framework—can be used in construction. Consistent separation reduces contaminants, lowers transport volumes, and improves reuse.

Equipment selection in the context of the CEM I matrix and application area

The choice and sequencing of techniques depend on cross‑section, reinforcement ratio, accessibility, and the expected brittleness of the CEM‑I matrix:

• Concrete demolition and special demolition: Combine concrete splitters for crack initiation and concrete pulverizers for controlled removal; reinforcement is separated with steel shear or Multi Cutters.
• Building gutting and concrete cutting: Local biting at openings, door, and shaft areas; where required, add core drilling and splitting to reduce loads.
• Rock excavation and tunnel construction: For shotcrete linings made with CEM‑I systems, splitting cylinders help create relief cuts before pulverizers remove the shotcrete in sections.
• Special demolition: In areas with sensitive surroundings or strict vibration limits, splitting technology enables low‑vibration, precise deconstruction.

Energy demand, hydraulics, and process stability

The forces required for crack formation and material separation increase with the strength and toughness of the CEM‑I matrix. Consistently available hydraulic power ensures reproducible cuts and splitting operations. A supply matched to the cross‑section via a hydraulic power pack shortens cycle times and avoids peak loads that could lead to unwanted fracture paths.

Occupational safety and environmental aspects

During the deconstruction of CEM‑I concrete, dust, noise, and vibrations are generated. Proven measures include low‑dust working practices, local dust extraction, the use of water where physically feasible, and compliance with applicable safety regulations. The resulting material must be recorded and disposed of or recycled according to its classification. Legal requirements can vary by project and region; therefore, careful, forward‑looking planning is essential.