Injection method

Injection methods are a central tool for the preservation of structures, ground improvement, and controlled demolition. By purposefully grouting mineral suspensions or reactive resins into cracks, joints, pore spaces, and voids, components can be sealed, stabilized, or structurally repaired to restore load transfer. In conjunction with the applications of Darda GmbH—for example in concrete demolition and special demolition, in interior demolition and concrete cutting, as well as in rock breakout and tunnel construction—injections enable safe and predictable workflows: they reduce uncontrolled water ingress, minimize detachment and edge spalling, and create stable boundary conditions for working with concrete pulverizers, hydraulic splitters, or other hydraulic tools.

Definition: What is meant by injection method

Injection methods refer to the pressure-controlled introduction of injection materials into structures or the ground. The objective is sealing (water stop, curtain formation), stabilization (increasing load-bearing capacity, crack filling), cavity filling (underfilling, backfilling), or load transfer (restoring bond). The injection is typically carried out via boreholes with installed packers, with mixing and pumping equipment controlling dosage, viscosity, and pressure. Typical injection materials are cement suspensions and microcements, silicate systems, and reactive resins such as polyurethanes, epoxy resins, or acrylate gels. Pressure and delivery quantity are selected to ensure penetration into the target structure without damaging components or triggering unwanted ground movements.

Application areas and connection to controlled demolition

Injections are used in new construction and existing structures, for repair and for deconstruction. In practice, they create safe conditions for mechanical cutting and splitting processes as encountered in combination with concrete pulverizers, hydraulic splitters, rock wedge splitters, hydraulic demolition shear, high-precision Multi Cutters, steel shear or tank cutter from Darda GmbH. In concrete demolition and special demolition, injections stabilize edge zones, fill voids behind slabs or walls, and reduce water ingress, allowing concrete parts to be separated precisely and then processed in a controlled manner with concrete pulverizers. In interior demolition and concrete cutting, contact and curtain injections improve the dimensional accuracy of saw and cut joints, reduce spalling, and ensure dry work areas. In rock breakout and tunnel construction, pre-injections secure the rock mass, reduce water pressure, and seal fissures, facilitating low-settlement splitting with rock and concrete tools and precise reprofiling with hydraulic cutting tools. In natural stone extraction, fissures can be bonded or sealed to promote defined fracture patterns for subsequent splitting techniques. For special demolition—for example in sensitive existing structures, in ATEX zone environments, or under confined inner-city conditions—low-emission grouting supports the planning of quiet, low-vibration workflows.

Overview of methods and injection materials

Mineral injections

• Cement suspensions: For cavity filling, curtain and contact injections; well suited to larger pores or fissures and to ground (gravels, sand-gravel mixtures). Pumpable, economical, with penetrability controlled by water-to-cement ratio and fines content.
• Microcement: Finer grinding enables penetration into finer pores and hairline cracks; suitable for dense concrete, masonry with finer capillaries, or slightly fissured rock.
• Silicate systems: Mineral, partly gel-forming, for stabilization and sealing in fine-grained soils; gelation depends on the formulation.

Reactive injections

• Polyurethane resins (PU): One- or two-component, water-reactive (foaming for water stop) or compact (elastic to rigid) for crack sealing and filling. Suitable for dynamically stressed cracks and water-bearing joints.
• Epoxy resins (EP): High strength and stiffness, for structural crack filling in dry to slightly damp concrete. Improves load transfer prior to targeted deconstruction.
• Acrylate gels (acrylates): Very low viscosity, adjustable gel time, for curtain injections in fine-grained soils or behind waterproofing layers.

Process types

• Crack injection (low pressure): Targeted grouting of cracks/joints in concrete and masonry; packer installation along the crack, pressure maintained until complete filling, documentation of exit points.
• Curtain injection: Area-wide sealing layer behind structures; forms a watertight curtain, for example behind basement walls or tunnel linings.
• Contact injection: Backfilling of voids between inner linings, facing shells, or linings and the substrate; establishes a full-surface bond.
• Compaction and stabilization injection: Increasing load-bearing capacity in the ground by filling and partial compaction; suitable for settlement reduction in existing urban environments.
• Compensation injection: Controlled settlement or uplift management by segmental grouting under monitoring; minimally invasive, suitable in urban settings.

Workflow and equipment

Preliminary investigations and planning

Prior to execution, structural diagnostics and ground investigations are carried out: crack widths and depths are recorded, water pathways identified, and material properties (density, pore structure, moisture) determined. In the ground, soundings, laboratory tests, and, where appropriate, permeability tests provide indications of penetrability and required formulations.

Drilling pattern, packers, and mixing technology

• Drilling pattern: Grid, angle, and depths are aligned with component thickness, crack path, target zone, and grout flow path. For components to be processed with concrete pulverizers, the drilling pattern is chosen so the later separation joint is not weakened but is purposefully prepared.
• Packers: Mechanical or adhesive packers for concrete; sleeve packers for masonry/ground. Check valves prevent backflow.
• Mixing and pumping technology: Homogeneous mixtures, controlled delivery, and pressure limiting are essential. Logging of pressure, volume, and time supports quality assurance.

Grouting, control, and completion

1. Pre-wetting or pre-cleaning of the bore channels (depending on the system).
2. Sequential injection from the deepest/most distant packer to the next (or vice versa, depending on the concept) to control flow paths.
3. Pressure hold until defined criteria are reached (volume, visible exit, pressure stability).
4. Remove packers, seal the boreholes. Remove excess material, visual inspection, and, if necessary, re-injection.
5. Documentation: formulations, batches, temperatures, pressures, quantities, exit points, and test results are recorded.

Planning, design, and documentation

The design is governed by the objective (sealing, stabilization, restoration of bond), material selection, and boundary conditions (moisture, temperature, movement). Key parameters include viscosity, gel or setting time, reactivity with water, particle size distribution for mineral systems, and permissible injection pressures. For subsequent processing with hydraulic splitters or concrete pulverizers, the load and cut line are coordinated so that splitting or fracture edges are purposefully guided. Trial injections and tests (e.g., leakage tests, exploratory drilling, extraction of concrete cores, rebound hammer as an orientation value) increase planning reliability. Structured documentation is part of quality assurance and forms the basis for the subsequent deconstruction or fit-out sequence.

Interfaces with concrete pulverizers and hydraulic splitters

Stabilizing and sealing before separation

Before separating wall or slab segments, a contact or curtain injection can close voids and minimize water ingress. This keeps cut joints dimensionally accurate, and components can be released precisely with concrete pulverizers or purposefully split with hydraulic splitters without uncontrolled spalling.

Crack injection for load redistribution

Crack injections with EP or PU structurally restore load-bearing bond in critical areas. This enables defined load redistribution so that subsequent steps—such as size reduction with concrete pulverizers, severing with hydraulic demolition shear, or the use of Multi Cutters—can proceed predictably and safely.

Boundary conditions for hydraulic tools

Drying via water stop injections improves visibility and reduces splash, which is advantageous when working with steel shear and tank cutter as well as when splitting concrete components. Purposeful backfilling behind façade or tunnel inner linings prevents secondary breakage when rock wedge splitters or concrete pulverizers operate close to edges.

Advantages, limits, and risks

• Advantages: Clear control of flow paths, low vibration levels, work in existing structures often possible during ongoing operations, improvement of watertightness and load-bearing capacity, predictable preparation for mechanical cutting and splitting processes.
• Limits: Very fine cracks below the penetration threshold, heavily contaminated or open cracks with continuous material loss, highly dynamic crack movements. With high water inflow, formulation adjustments and multi-stage approaches are required.
• Risks: Unwanted ground heave at excessive pressures, material discharge at undetected locations, insufficient adhesion on damp or contaminated flanks, chemical sensitivity of resins. Careful pressure control and a stepwise grouting strategy mitigate these risks.

Occupational safety and environmental protection

When handling injection materials, personal protective equipment, ventilation, and careful material logistics are essential. Reactive resins are handled in accordance with manufacturer specifications; spilled material must be collected and disposed of properly. Water-side protection measures prevent entry into soil and water bodies. Low emissions and low vibrations support safe operation in sensitive areas and match the quiet, controlled working methods with Darda GmbH’s hydraulic tools. Legal requirements, technical rules, and regulatory stipulations must be reviewed and observed for each project.

Standards and technical rules at a glance

For injections in concrete structures, European product and application standards as well as national guidelines are relevant, defining requirements for materials, processing, testing, and documentation. In the field of waterproofing and the repair of concrete components, recognized regulatory frameworks provide guidance for selection, design, and execution. For injections into the ground, geotechnical codes describe procedures, verifications, and controls. These requirements are project-specifically interpreted and implemented by qualified specialists.

Practical scenarios

• Concrete demolition and special demolition: Before lifting a concrete slab, voids are backfilled and cracks injected. Result: reduced secondary breakage, precise gripping with concrete pulverizers, controlled sizing without edge spalling.
• Interior demolition and concrete cutting: Curtain injection behind an existing wall stops water ingress. Dry separation joints facilitate follow-up work with hydraulic demolition shear and Multi Cutters.
• Rock breakout and tunnel construction: Pre-injection in loose rock lowers water inflow and increases cohesion. This enables low-settlement opening of separation joints with hydraulic splitters and dimensionally accurate reprofiling.
• Natural stone extraction: Grouting fissures to promote defined fracture lines. Subsequent use of rock wedge splitters yields large, predictable blocks.
• Special demolition: In tank-adjacent areas, sealing injections prevent media from entering the work area. Subsequent work with steel shear or tank cutter is carried out with reduced risk.

Material selection and formulation tuning

The choice of injection material depends on crack width, moisture, movement characteristics, chemical exposure, and objective. Cements and microcements are suitable for filling and stabilization, epoxy resins for structural repairs, polyurethanes for water-bearing cracks with water stop and elastic sealing, acrylate gels for large-area, very low-viscosity sealing. Decisive factors are viscosity, gel or setting time, bond strength, and compatibility with the substrate. The formulation is validated in trial injections; for ground injections, staged plans with varying viscosity and pressure control can be effective.

Quality assurance and performance verification

Effective quality assurance combines monitoring of process parameters (pressure, volume, time) with component-related testing. Visible exits, leakage tests, measurements at control boreholes, and, where appropriate, concrete cores to assess injection reach are common. For sealing injections, effectiveness is assessed via moisture or degree of dampness; in the ground, settlement and uplift measurements provide information. These verifications form the basis for continuing immediately afterward with concrete pulverizers, hydraulic splitters, or other hydraulic tools.