Flowing concrete is a highly workable concrete that de-aerates under its own weight without vibrating and completely fills the formwork. It is used especially where the reinforcement is dense, geometries are complex, or a uniform, low-void surface is required. In practice, flowing concrete is found in structural engineering (building construction) as well as in precast elements and in tunnel structures. For later deconstruction, the concrete structure (matrix) of flowing concrete has noticeable consequences: dense matrices, high early and final strengths, and possible fibre reinforcement influence the choice of gentle methods such as concrete pulverizer, hydraulic splitter (wedge), and hydraulic demolition shear as well as the drive power of the hydraulic power pack from Darda GmbH.
Definition: What is meant by flowing concrete
Flowing concrete refers to a concrete with very high flowability and a pronounced tendency to self-compact. It distributes under its own weight, envelops the reinforcement, and de-aerates without mechanical compaction. It is often referred to as self-compacting concrete (SCC); in international usage the abbreviation SCC (Self-Compacting Concrete) is common. Typical are large spread diameters, short flow times, and a composition with increased fines content as well as high-performance plasticizers and stabilizing admixtures. The goal is a homogeneous, low-segregation matrix with low porosity and high surface quality.
Properties, composition and standards
Flowing concrete is based on a fine grading curve, low viscosity, and controlled stability. Decisive are the water-to-binder ratio, the type of plasticizers (e.g., modern PCE systems), and, where applicable, viscosity modifiers that limit the risk of segregation. Strength classes range, depending on the design, from common classes up to high-performance concrete (HPC) qualities. In practice, consistency (spread, flow time) and stability (sieve stability, blocking tendency) are monitored. It is common to follow the relevant technical rules (e.g., DIN EN 206/DIN 1045-2 in the currently valid version).
Rheology and stability
Flowing concrete exhibits pronounced flow behavior with a low yield stress and sufficiently high plastic viscosity. This allows it to fill tight reinforcement gaps without segregating. Too low a viscosity favors segregation and bleeding; too high a viscosity reduces self-compaction. The balance between flowability and stability is the key criterion.
Matrix and mechanical properties
The combination of low air content and a dense matrix leads to smooth, low-void surfaces, good compressive strength, and often increased surface hardness. In deconstruction situations this can result in more brittle fracture patterns with limited crack branching, which affects the action of concrete pulverizer and hydraulic splitter (wedge). With fibres (steel or synthetic) the cracking behavior changes: energy absorption increases, and the post-crack behavior becomes more ductile, which must be considered during separation and splitting.
Durability and concrete cover
Thanks to good de-aeration and uniform concrete cover, resistance to chloride contamination and concrete carbonation is positively influenced. For deconstruction this often means tightly adhering cover layers and dense edge zones, which can require higher initial loads for concrete pulverizer.
Production, transport and placement
The production of flowing concrete requires precise dosing and mixing technology that ensures a homogeneous distribution of the binder and the fine aggregates. Transport and placement are usually via pump. Neither internal vibrator nor vibrating screed are intended; instead, controlled placement rates, suitable pouring heights, and careful concrete curing are selected.
Mix design
- Increased fines content (cement, supplementary materials such as fly ash, ground granulated blast-furnace slag, or fillers) to stabilize the mortar skeleton
- High-performance plasticizers for large spreads at a moderate w/b ratio
- Viscosity modifiers where necessary to reduce segregation tendency
- Grading curve with sufficient mortar volume and tuned aggregate gradation
Placement and formwork pressure
Due to the high flowability, increased fresh-concrete-related formwork pressures can occur. Formwork is designed accordingly and executed with tightness. Placement is carried out in continuous lifts; pouring points and rates are chosen to avoid air entrapment.
Quality assurance and test methods
Fresh-concrete-related tests target flowability, blocking tendency, and stability. They serve both mix development and construction site monitoring.
- Spread diameter and T500 time: measures for flowability and initial viscosity
- V-funnel: assessment of flow time and viscosity
- L-box/J-ring: evaluation of reinforcement passing ability and blocking tendency
- Sieve stability test: estimation of segregation tendency
Hardened-concrete parameters
Compressive strength, tensile strength (splitting tensile), modulus of elasticity, and surface hardness are determined as for conventional concrete. Density, water absorption, and porosity serve as indicators for durability and the expected fracture behavior during deconstruction.
Typical application fields of flowing concrete
Flowing concrete is preferred wherever geometry, reinforcement density, or surface requirements make conventional placement difficult.
Building construction and structural engineering
- Columns, walls, and cores with dense reinforcement
- Flat slabs with a high density of downstand beams
- Architectural fair-faced concrete with a homogeneous surface
Tunnel construction and infrastructure
- Inner linings with complex reinforcement
- Riverbank and retaining walls with high durability requirements
- Precast segment rings and fitting pieces where compaction access is limited
Precast elements and special components
- Slender precast elements with low component thickness
- Elements with high surface requirements
- Components with insert density (e.g., built-in component, anchor)
Effects of flowing concrete on deconstruction and demolition
The properties of flowing concrete shape the choice of demolition technique. The dense, low-void matrix, possible fibre reinforcement, and the often increased reinforcement density lead to a preference for low vibration levels, controlled methods. In concrete demolition and special demolition as well as during gutting works and concrete cutting, hydraulic tools are used that introduce forces precisely and separate material selectively.
Concrete pulverizer: controlled crushing
Concrete pulverizer grip the component and crush it along weak zones. In flowing concrete, weakening is often found in joints, construction breaks, or deliberately introduced separation cuts. If steel fibre reinforcement is present, it influences the post-crack behavior; concrete pulverizer are then often combined with steel shear or Multi Cutters to cleanly cut exposed reinforcement or fibres. For select tasks, Concrete Crushers can provide comparable controlled crushing.
Hydraulic splitter (wedge): low-noise and low-vibration splitting
Hydraulic splitter (wedge), including rock splitting cylinders and hydraulic rock and concrete splitters, generate controlled tensile stresses in the component. In dense flowing-concrete matrices, predrilled hole patterns and the orientation of split lines can be planned so that the crack path is guided away from reinforcement zones. The method is particularly suitable in sensitive environments with strict emission requirements.
Hydraulic demolition shear, Multi Cutters and steel shear: safely separating steel content
The often high reinforcement density in components made with flowing concrete requires reliable cutting and shearing forces. Combination shears unite crushing and cutting functions; for massive bars or sections, dedicated steel shear are advisable. Multi Cutters support the separation of heterogeneous inserts, cables, and thin-walled steel parts.
Hydraulic power pack: power supply and sequencing
The hydraulic power pack provides the necessary power reserve for continuous work cycles. Appropriate hydraulic power units help maintain consistent performance. With dense flowing concrete, one often begins with pre-cracking using a splitting technique and then applies the concrete pulverizer to release fragments in a controlled manner. Suitable sequencing reduces tool wear and emissions.
Special operations and industrial facilities
In industrial demolition work, flowing-concrete jackets can encase steel tanks, platforms, or enclosures. After exposing the concrete, metallic shells can be separated, depending on material thickness, with steel shear or a cutting torch. The sequence of splitting, pulverizer demolition, and steel cutting ensures selectivity.
Planning in existing structures: investigation, documentation and separation cuts
Before deconstruction, a building-diagnostic investigation is recommended. The aim is to identify the mix, strength, reinforcement ratio, any fibres, and the location of critical inserts. Core drilling, rebound hardness tests, and reinforcement location surveys provide indications of the material response under demolition loads. Based on this, separation cuts and split-hole patterns are planned.
- Material and reinforcement survey, including possible fibre content
- Definition of separation joints, split lines, and gripping points
- Selection of tools (concrete pulverizer, hydraulic splitter (wedge), hydraulic demolition shear) and sizing of the hydraulic power pack
- Definition of demolition sections and lifting safety (load calculation, fixed points)
- Emissions concept for noise emission, low vibration levels, and dust suppression
Work organization, emissions and environmental aspects
For structures made of flowing concrete, a low-emission working method is advantageous. Splitting and pulverizer demolition generate low vibrations and reduce secondary damage. During cutting and crushing, dust and fine dust are limited by water mist or dust extraction. Recyclable fractions (concrete, reinforcing steel, inserts) are collected separately. Information on local requirements and permits must always be observed; specific requirements may vary by project and region.
Tool conservation and safety
- Controlled pre-separations reduce notch stresses and increase the tool service life of concrete pulverizer
- Adapt split-hole diameter, depth, and spacing to component thickness and reinforcement layout
- Perform rebar cutting on exposed reinforcement with steel shear or Multi Cutters
- Regularly check the hydraulic power pack and hydraulic hose line connections
Practical guide for concrete demolition with flowing concrete
The following points have proven effective in practice to process components made of flowing concrete precisely and resource-efficiently:
- Sequence: Investigation → Pre-separation/splitting → Crushing with concrete pulverizer → Separate rebar cutting
- Crack control: Plan split lines so that cracks run along weaker zones and away from heavily reinforced areas
- Force dosing: Increase hydraulic pressure step by step to form brittle fractures in a controlled way
- Fibre concrete: For steel fibres, provide cutting techniques; for synthetic fibres, consider the change in post-crack behavior
- Tunnel and inner-city operations: Use low vibration levels via splitting devices and concrete pulverizer; perform cutting operations in a targeted, sectional manner
Disposal and recycling
Removed flowing concrete can be processed analogously to conventional concrete. The dense matrix generally yields high-quality concrete rubble that can be processed into recycled concrete. Metals are separated from the composite with steel shear or Multi Cutters and discharged sorted by type. Specifications on waste law and the recycling rate must generally be observed; binding requirements are determined by the applicable regional regulations.