Cem v

CEM V is a clinker-reduced composite cement with multiple main constituents. In practice it influences fresh and hardened concrete properties, ageing behavior, and the deconstruction of structural components. For planned concrete demolition using concrete pulverizers, hydraulic rock and concrete splitters, and the use of a hydraulic power pack, it is crucial to know how CEM V concretes separate under load, how cracks propagate, and which cutting and splitting strategies are suitable. The main topic here is CEM V cement.

Definition: What is meant by CEM V

CEM V cement is a composite cement according to European cement standards that consists of Portland cement clinker and at least two additional main constituents. Typical are combinations of ground granulated blast-furnace slag (latent hydraulic) and pozzolanic components such as fly ash or natural pozzolans. CEM V usually appears as CEM V/A and CEM V/B, which differ in clinker content. It is supplied in common strength classes (e.g., 32.5; 42.5; 52.5) with normal or rapid early strength development (N/R). The formulation targets robust durability with reduced heat of hydration and a lower clinker demand.

Composition and references to standards

The main constituents of CEM V are Portland cement clinker, blast-furnace slag, and pozzolanic additions (such as fly ash or natural pozzolans). Depending on the standardized variant, fine constituents like limestone powder or microsilica may be present in limited amounts. The standards specify ranges for main constituents, quality characteristics (e.g., sulfate content, chloride limit), strength classes, and conformity assessment. Exact recipes vary by plant and cement supplier but remain within prescribed limits.

Characteristic for CEM V are:

• clinker-reduced composition with a share of slag and pozzolans,
• lower heat of hydration compared to pure Portland cements,
• often slower early strength development with good ultimate strengths,
• potentially dense microstructure and favorable resistance to chloride ingress.

Material properties of CEM V concretes

The properties result from the combined hydration of clinker phases and the reaction of supplementary constituents with calcium hydroxide. For planning, execution, and deconstruction, the following are particularly relevant:

Fresh concrete

• Workability: CEM V concretes often show good workability. The use of modern superplasticizers is nevertheless common.
• Setting: Hardening tends to be more moderate; early strength gain may be delayed.
• Heat of hydration: Reduced, which can mitigate deformation and cracking risks in massive members.

Hardened concrete

• Strength: Favorable ultimate strengths; early strengths lower depending on the mix. In older components, a very dense matrix can be expected.
• Durability: Good resistance to chloride ingress and often improved tightness; sulfate resistance depends on the exact composition.
• Shrinkage/creep: Depending on the formulation, favorable; with lower heat of hydration often associated with reduced self-induced cracking in massive cross-sections.

Relevance of CEM V for demolition, cutting, and splitting

For deconstruction using concrete pulverizers, stone and concrete splitting devices, and in combination with a hydraulic power pack, the mechanical behavior of the concrete is decisive. CEM V concretes—especially at advanced age—can develop a dense matrix and high bond to the aggregate. This affects crack formation, fracture surfaces, and the process energy required.

Concrete pulverizers: separation behavior and tactics

• Crack initiation: In dense CEM V matrices, cracks more often propagate along interfaces to the coarse aggregate or along reinforcement planes. Targeted positioning of the jaws at edges, notches, or existing joints facilitates the break.
• Jaw geometry and contact points: Aggressive tooth geometries support scoring of the cover layer. For thick members, a sequential “opening up” along the weakest cross-sections is advisable.
• Reinforcement: Bond in CEM V concrete can be very high. Cutting the reinforcement is best done after first breaking the concrete cover to create access.
• Tactical pre-weakening: Preparatory cuts or small splitting holes reduce the required jaw force and improve crack propagation.

Stone and concrete splitting devices: crack control in CEM V concrete

• Borehole spacing: The dense matrix often requires closer spacing and careful alignment in the intended fracture direction. Borehole diameter and insertion depth must be matched to member thickness and desired fragment size.
• Hydraulic pressure and sequence: Gradually increasing splitting pressure guides cracks in a controlled manner. Even triggering in rows promotes clean separation joints.
• Interaction with concrete pulverizers: After pre-weakening by splitting, concrete pulverizers can produce coarse and fine fragmentation more quickly. This reduces noise, vibration, and secondary damage.

Impact on selected application areas

Concrete demolition and specialized deconstruction

• Massive members: Due to reduced heat of hydration, self-induced cracks are rarer; more energy may be needed to create the initial break. Splitters help establish defined predetermined fracture lines.
• Members with high durability: Dense CEM V concretes require precise attack surfaces. Concrete pulverizers work efficiently when edges and weaknesses are predefined.

Strip-out and cutting

• Combination with saw cuts: Separation cuts establish clear crack stoppers. Concrete pulverizers then enable controlled lifting-out.
• Edge areas: In areas with a brittle cover layer, a gentle jaw approach is advisable to minimize spalling at existing edges.

Rock demolition and tunnel construction

• Cast-in-place and segment lining structures: CEM V concrete in linings often exhibits low permeability. Splitters establish defined separation planes; concrete pulverizers take over fragmentation.

Natural stone extraction and special applications

• Temporary works: Foundations or concrete pedestals made of CEM V concrete can be released with low disturbance by pre-drilling and splitting before concrete pulverizers adjust piece sizes.

Identifying and assessing CEM V concrete in existing structures

On site, unambiguous identification without documentation is not trivial. Clues include:

• Documents: Delivery notes or structural calculations often state the cement type.
• Construction history: CEM V may have been used in structures with a focus on durability or massive construction.
• Material appearance: A dense, homogeneous matrix and good edge retention indicate clinker-reduced, dense systems. This is not proof but supports tactical choices.

For safety-relevant decisions, investigations (e.g., core drilling, laboratory testing) are useful to determine strength, density, and reinforcement layout.

Implications for equipment use and hydraulics

• Force demand: Dense CEM V matrices may require higher initial forces. Adjusted pressure stages on the hydraulic power pack support a controlled start to crack formation.
• Sequencing: Alternating splitting and jaw strokes reduces peak loads and preserves cutting edges.
• Maintenance: Abrasive fines from the matrix require regular cleaning and visual checks on jaws and splitting wedges.

Sustainability, reuse, and recycling

Due to the reduced clinker content, CEM V generally has a more favorable CO₂ balance compared to pure Portland cement. During deconstruction, producing targeted grain sizes is important to facilitate concrete recycling. A combination of stone and concrete splitting devices for predefined cracking and concrete pulverizers for size adjustment often yields cubic, well-sortable fractions and reduces fines. This supports high-quality use as recycled aggregate.

Typical challenges and practical solutions

• Slow early strength in recent structures: In younger members the matrix is tougher. Solution: Pre-weakening with small splitting holes, then jaw stroke.
• High bond to reinforcement: Solution: Use the concrete pulverizer first to open, then separate the reinforcement, followed by fragmentation.
• Unpredictable crack path: Solution: Drill patterns with closer spacing and defined orientation; sequential pressure increase during splitting.

Checklist: preparation for demolition work on CEM V concrete

1. Review documentation: cement type, strength class, construction age, reinforcement drawings.
2. Analyze the member: thickness, supports, joints, edges, embedded items.
3. Trial cut or trial drilling: material identification, crack tendency, aggregate skeleton.
4. Define the approach: sequence of splitting, cutting, jaw strokes; target fragment sizes.
5. Configure hydraulics: pressure stages, sequencing, safety margins.
6. Protective measures: dust minimization, noise reduction, shoring, cordoning.
7. Check tool condition: jaws, splitting wedges, hoses, couplings.
8. Monitoring: crack development, member movement, load transfer.

Safety and general notes

Work on load-bearing components requires careful planning and appropriate safeguarding measures. This includes shoring, controlled load redistribution, and a coordinated approach to splitting and jaw operations. Dust and noise protection must be considered; a step-by-step approach with moderate hydraulic pressures supports controlled crack guidance and reduces environmental impacts.