Hollow concrete blocks are common masonry units made of normal concrete or lightweight concrete with internal hollow cores. They combine a favorable ratio of self-weight to load-bearing capacity with good workability. In new construction, conversion, and deconstruction, they appear wherever walls are built economically, quickly, and robustly. For professional handling of hollow-block masonry, knowledge of composition, material properties, and typical processing steps is crucial—along with the proper selection of tools for cutting, splitting, and demolition, such as the use of concrete demolition shear (see HCS8) or hydraulic rock and concrete splitters in the context of concrete demolition and special demolition.
Definition: What is meant by a hollow concrete block
A hollow concrete block is a manufactured masonry unit made of concrete whose cross-section consists of webs and voids (hollow cores). Depending on bulk density class and aggregates (e.g., pumice, expanded clay, or natural gravel), a distinction is made between normal concrete and lightweight concrete hollow blocks. The block is laid in courses; the cavities generally remain empty; for special requirements, they can be purposefully filled or cast with concrete. Hollow concrete blocks are used for load-bearing and non-load-bearing masonry and are available in various formats, compressive strength classes, and bulk densities.
Composition, formats, and material properties
Hollow concrete blocks consist of outer webs and one or more inner webs separating the hollow cores. The geometry reduces self-weight, improves thermal and airborne sound insulation, and still allows high compressive capacity in the wall direction. Formats range from slender units for non-load-bearing partition walls to large-format units for load-bearing exterior and interior walls. Lightweight concrete variants use porous aggregates to reduce thermal conductivity and weight, while normal concrete blocks offer higher bulk densities and improved sound insulation.
Typical formats and key values
- Dimensions: common examples include 490 × 240 × 240 mm, 490 × 300 × 240 mm, or 365 × 240 × 240 mm; wall thicknesses are based on structural and building physics requirements.
- Compressive strength classes: typically around 2–20 N/mm² (unit), depending on concrete mix and manufacturing process.
- Bulk density classes: lightweight concrete approx. 0.8–1.4 kg/dm³, normal concrete approx. 1.8–2.2 kg/dm³.
- Thermal conductivity: lower for lightweight concrete, higher for normal concrete; exact design is project-specific.
- Sound insulation: more massive masonry provides increased airborne sound insulation; joint quality is essential.
- Fire protection: mineral, non-combustible, classification per applicable standards is possible.
Building physics and connection details
The hollow cores influence thermal bridges and sound insulation. Careful bed and head joints, system-compliant corner details, and suitable fasteners are decisive. For heavy loads, load transfer into the webs must be ensured; where required, cores are selectively filled. For installation chases, web thicknesses must be respected to avoid impermissible weakening of load-bearing capacity.
Hollow concrete block in new construction: execution and detailing
In new construction, hollow concrete blocks are laid in bond. Depending on the system, thin-bed or general-purpose mortar may be used. Bed joints are to be fully filled; head joints can, depending on unit and system type, be interlocked or mortared. Openings for doors and windows receive lintels or supports with sufficient bearing length.
Reinforcement and infill concreting
In areas with concentrated loads, edge zones, or seismic action, partial concreting of cores with or without reinforcement can be specified. Manufacturer guidance for the units and the designer’s verifications are decisive. Proper compaction prevents voids.
Fastenings in hollow-block masonry
Mechanical or chemical fastenings should be placed in the webs. Anchors installed in cavities require approved mesh sleeves or backfilling. For high loads, filling the cores near the fastening point is advisable. On-site proof loads improve the reliability of the detail.
Processing, cut-outs, and openings
When creating chases, penetrations, or door openings in hollow-block masonry, a low-vibration, controlled material removal is advantageous. Depending on wall thickness, reinforcement content, and surrounding constraints, different methods are appropriate. Hydraulic splitters are suitable for sharp, nearly vibration-free openings, especially in unreinforced or lightly reinforced masonry, while a concrete demolition shear offers a good compromise between speed and control where access and sufficient grip clearance are available.
Procedure for precise openings
- Check load-bearing capacity and plan temporary shoring where load redistribution may occur.
- Mark layout lines and cut edges cleanly; account for joint layout and webs.
- Pre-drilling or core drilling at corners limits crack formation and enables defined edges.
- Targeted splitting with hydraulic cylinders in rows of boreholes reduces dust and vibration.
- For selective deconstruction: separate materials by type, separate units and mortar, keep transport routes low-dust.
Deconstruction of hollow-block masonry in practice
In concrete demolition and special demolition, hollow-block masonry is common in partition walls, shaft walls, and infill panels. Decisive factors include reinforcement level, accessibility, adjacent components, and emission limits (dust, noise, vibration).
Tool selection for deconstruction
- Concrete demolition shear: suitable for biting off masonry segments step by step, good edge control with moderate reinforcement content.
- Hydraulic splitters: for low-vibration, controlled separations along defined rows of boreholes, particularly for work in sensitive environments.
- Combination shears and multi cutters: versatile in gutting contexts when materials are mixed (masonry with inserts, light steel sections).
- Steel shear: for metallic inserts; they complement masonry deconstruction but are not intended for the stone itself.
- Hydraulic wedge splitter: pinpoint splitting of thick wall sections or in braced zones.
Appropriately sized matching hydraulic power units provide the required energy. The choice of power pack and its matching to the connected tools influences working speed, noise emission, and the overall emissions profile.
Use cases and typical tasks with hollow-block masonry
Hollow concrete blocks appear across different project types. This yields practical applications for Darda GmbH equipment:
- Concrete demolition and special demolition: selective removal of load-bearing and non-load-bearing walls; splitting, biting, and defined deconstruction in construction stages.
- Building gutting and cutting: openings for service runs, door breakthroughs, stairwell adjustments; low vibration levels using splitting techniques or shear-based removal.
- Special applications: work in sensitive areas such as hospitals, laboratories, or listed buildings; minimizing dust and noise through controlled splitting and finely dosed shear work.
Occupational safety, emissions, and environmental protection
Dust, noise, and vibration are key aspects when processing hollow concrete blocks. Low-dust working—e.g., by wet drilling, targeted splitting, and short material paths—protects personnel and surroundings. Low vibration levels are advantageous in occupied or sensitive existing buildings. Personal protective equipment, extraction technology, and coordinated work sequences reduce risks. Legal requirements and local limit values must be considered on a project-specific basis.
Gentle interventions in existing structures
Splitting along pre-drilled rows of holes creates defined fracture edges and limits crack propagation. Concrete demolition shear allows finely dosed material removal, which is particularly important near adjacent finishes or installations. Short grip paths, clear demolition edges, and an orderly sequence of steps increase execution safety.
Sustainability, reuse, and recycling
Hollow-block masonry can generally be processed into recycled construction material. Clean construction waste separation—sorted into concrete, mortar residues, metal inserts, and any infill—improves the quality of the recycled aggregate. In practice, gently releasing larger segments by splitting or shear-wise dismantling helps minimize fines and contamination. This can achieve higher recycling rates.
Planning for deconstruction
It is worth considering later deconstruction already during execution planning: documented material qualities, filled or unfilled cores, inserts, and connection details. Subsequent use of hydraulic splitters or a concrete demolition shear benefits from clear information on wall build-up, reinforcement, and joint pattern.
Planning, structural analysis, and interfaces
The load-bearing behavior of hollow-block masonry is based on compressive load transfer in the wall direction. Projections, chases, and openings must be designed so the webs are not impermissibly weakened. For later openings, substitute load paths via lintels, beams, or shoring must be ensured. In case of doubt, project-specific verifications are required; binding statements are only possible in the context of the respective structure.
Interfaces with fit-out trades
Installations benefit from void areas in the cores; however, webs must not be weakened indiscriminately. Fastenings are preferably placed in webs; for heavy loads, core filling is to be provided. Precise openings using splitting or shear techniques facilitate a coordinated workflow with electrical, plumbing, and ventilation trades.
Tool technology at a glance: splitting, cutting, gripping
The choice of method depends on wall thickness, reinforcement, accessibility, and emission requirements. Hydraulically powered tools enable controlled, reproducible results:
- Hydraulic splitters: borehole-based, low-vibration separation; advantageous for defined edges and reduced secondary damage.
- Concrete demolition shear: gripping, pressure-based removal with high controllability; good for segmenting and profiling openings.
- Combination shears and multi cutters: useful for mixed components and gutting when multiple materials must be processed in one pass.
- Hydraulic wedge splitter: single- or multi-point splitting for massive wall sections or filled cores.
- Hydraulic power pack: energy source and pace setter; proper sizing supports continuous work with a constant pressure level.
Typical error patterns and practical notes
Boreholes placed too close to edges, inadequate shoring at openings, and weakening of load-bearing webs are common errors. Uncontrolled impacts also lead to crack fans and spalling. A proven sequence is layout marking, corner drilling, defined splitting, and subsequent profiling of the opening with the concrete demolition shear. Where metal parts appear within wall areas, complementary shear tools support separation.
Quality assurance on site
Trial sections, documented equipment settings, and a clear work sequence improve result quality and schedule reliability. Regular inspection of cut edges and remaining cross-sections prevents unintended losses of load-bearing capacity. Rework is preferably performed with shear-based fine finishing rather than percussive methods.
Practice-oriented examples
In building gutting and cutting, new door openings are often created in hollow-block walls. Procedure: layout marking, corner drilling, splitting sequence, removal of segments, edge profiling with the concrete demolition shear. In concrete demolition and special demolition, non-load-bearing hollow-block walls can be removed section by section with the concrete demolition shear—low vibration levels and controlled. In special applications (e.g., vibration-sensitive environments), splitting with hydraulic cylinders enables work with reduced vibration and minimized dust generation.