Aac block

AAC block is a lightweight, mineral masonry unit with a fine, uniform pore structure. It combines low bulk density with good thermal insulation and high dimensional accuracy. In new construction it is used for load-bearing and non-load-bearing walls; in existing buildings it is frequently found in interior walls and shear panels. For deconstruction, gutting works and selective concrete demolition the material characteristics are decisive, as they influence the choice of suitable methods and tools – especially when working with concrete demolition shears or stone splitters and concrete splitters from Darda GmbH, which operate with low vibration levels and in a controlled manner. In practice, low-vibration separation limits secondary damage to adjacent components and supports compliance with emission limits during refurbishment.

Definition: What is meant by an AAC block?

AAC block (also called autoclaved aerated concrete or gas concrete) is a steam-cured lightweight material based on quartz sand, lime and or cement, water and a foaming agent. Typically, a small amount of aluminum powder reacts in the fresh mix and releases hydrogen, which escapes during curing and leaves finely distributed, closed air pores. The resulting pore system lowers the bulk density and improves thermal insulation. AAC blocks are usually supplied as dimensionally accurate plan blocks with smooth bedding faces for thin-bed mortar. They differ from lightweight concrete blocks: autoclaved aerated concrete is not dense but porous and is autoclaved; its compressive strength is moderate, its fire protection performance is excellent, and its vapor permeability is high.

On-site identification and differentiation

• Appearance and feel: light grey to white, low self-weight, can often be scratched with a nail or trowel edge.
• Fracture image: uniformly porous, no visible coarse aggregate; fracture edges can be brittle.
• Sound when tapped: rather dull compared to dense concretes or clay bricks.
• Distinction from lightweight aggregate concrete: AAC is porous and autoclaved, not aggregate-rich; lightweight aggregate concretes show visible aggregate and are harder to cut.

Material properties and production of AAC blocks

The microporous structure shapes site practice – from processing to later deconstruction. The following properties are decisive for planning and execution:

Production at a glance

1. Mix raw materials: quartz sand flour, binders (lime cement), water, foaming agent.
2. Foaming: the reaction releases hydrogen, forming evenly distributed pores.
3. Pre-hardening: the “green” cake is cut into blocks stones.
4. Autoclaving: steam curing under pressure and temperature creates the final mineral phases.
5. Packing and quality control: dimensional checks, density strength class labeling, and palletizing.

Typical characteristic values

• Bulk density classes: approx. 0.30-0.70 kg dm³ (typical on site 0.35-0.60).
• Compressive strength classes: approx. 2-6 N mm², sufficient for many load-bearing walls in residential and office construction.
• Thermal conductivity: approx. 0.08-0.20 W m·K, depending on bulk density.
• Fire protection: non-combustible, very good fire resistance with appropriate wall thickness.
• Noise insulation: moderate; acoustic performance increases with bulk density and wall thickness.
• Moisture behavior: notable capillary water absorption – detailing for splash water and driving rain is crucial.
• Vapor diffusion: low µ-value (approx. 5-10), enabling vapor-permeable constructions.

Formats, system components and design notes

AAC blocks are offered as plan blocks, plan units and supplementary elements (U-blocks, lintels). The high dimensional accuracy allows thin-bed mortar (bed joint approx. 1-3 mm), which reduces thermal bridges. Vertical joints can be fully mortared or formed with tongue-and-groove systems depending on the product line. Load-bearing external walls can be built as single- or multi-leaf; combining with ring beams cast in place and reinforced concrete components is common. Movement and settlement joints must be planned in line with building geometry and substrate conditions.

Planning focal points

• Match wall thicknesses and strength class to loads, bracing and connections.
• Details at openings: load-bearing lintels, compression-resistant bearings, connections to slabs.
• Consider moisture and driving-rain protection for single-leaf external walls.
• Fixings: use suitable anchors for AAC, verify tension and shear loads.
• Thermal bridge control at ring beams, beam seats and window door reveals, including suitable insulation details.
• Check bracing and dynamic or seismic actions where applicable, and coordinate with ring beams and tie elements.

Applications in building construction

AAC block is suitable for load-bearing external and internal walls, non-load-bearing partitions, fire walls and facing shells. In existing buildings, partitions in sanitary and service cores are common, which are selectively deconstructed during gutting works. The combination of low weight and good workability makes AAC suitable for additions and refurbishments with tight logistics constraints.

Typical fields of use

• Housing: thermally insulating external walls, internal walls with good workability.
• Utility buildings: non-load-bearing walls and shafts with high fire protection requirements.
• Additions and conversions: low self-weight is structurally advantageous.
• Fit-out and refurbishment phases: partitions that can later be dismantled selectively with low emissions.

Processing and cutting on site

The soft matrix allows cutting with hand saw, band saw or masonry saws. Grooves for installations are milled or chiseled. Surfaces can be planed or rubbed to achieve flatness before thin-bed bonding. For precise adjustments, low-dust working with dust extraction is recommended, ideally using devices with effective filtration for fine mineral dust.

Influence on later deconstruction methods

The low strength and porous structure favor controlled removal. In selective deconstruction during gutting works and in concrete demolition and special demolition, manually guided, hydraulic handheld tools are often used that generate low vibration levels and release components in a targeted manner. Fasteners and anchors typically have lower pull-out resistance in AAC compared to dense concretes, which can facilitate disassembly when planned systematically.

Selective deconstruction: methods and tools

The choice of method is based on wall thickness, reinforcement, adjacent components and emission control. For AAC walls without reinforcement, the following approaches have proven effective, especially when finishes, installations or neighboring components must be preserved:

Low-vibration separation and removal

• Concrete demolition shears: controlled “nibbling” of wall sections, advantageous for segmental removal indoors with limited logistics. The low strength of AAC enables high removal rates with low reaction forces.
• Stone splitters and concrete splitters: application of splitting forces via borehole wedges or split cylinders. Suitable for introducing defined crack lines, opening wall panels and releasing connection areas, for example at reinforced concrete columns.
• Decoupling cuts and boreholes: relief cuts or core bores at interfaces help to pre-define break lines and to protect adjacent finishes.

Hydraulics and the system approach

Hydraulically driven hand tools require matching hydraulic power units. For combined deconstruction tasks – e.g., an AAC wall with an adjacent reinforced concrete ring beam – switching between concrete demolition shears, hydraulic wedge splitters and, where steel is exposed, steel shears can be useful. Low-emission, segmental removal is particularly advantageous in gutting works and concrete cutting as well as in special demolition in sensitive areas. Practical aspects include short hose runs to limit pressure losses, secure routing to avoid trip hazards and choosing power unit locations that minimize noise transmission.

Work sequence for controlled deconstruction

1. Component analysis: clarify wall thickness, any reinforcement, connections and installations.
2. Dust and fragment protection: plan enclosures, extraction and water mist.
3. Pre-weakening: introduce rows of boreholes for stone splitters and concrete splitters or relief cuts for concrete demolition shears.
4. Segmental removal: from top to bottom, continuously monitor structural stability.
5. Material separation: separate AAC, mortar residues and steel, keep transport routes short.
6. Documentation and waste tracking: record quantities and destinations to support recycling and regulatory compliance.

Interfaces with reinforced concrete and reinforcement

AAC walls often tie into reinforced concrete slabs, columns and ring beams. During deconstruction, transitions are relieved first. Concrete demolition shears can expose bearing areas; for the adjoining reinforced concrete, depending on boundary conditions, higher-performance concrete demolition shears or stone splitters and concrete splitters are used. Exposed reinforcement can then be cut with steel shears. Before severing reinforcement at supports or ring beams, ensure that alternative load paths or temporary shoring are in place and verified.

Occupational safety and emission control

The low self-weight reduces handling risks, yet dust and sharp fracture edges must be considered. Hydraulically operated shears and splitters enable a low-vibration approach. Protective measures include:

• Dust suppression: dust extraction, spot wetting, enclosed work areas.
• Noise reduction measures: prefer hydraulic tools, limit impact energy.
• Safety against uncontrolled tipping: segmental dismantling, shoring.
• Personal protective equipment and exposure control: respiratory protection in line with mineral dust silica limits, eye and hand protection against sharp edges.
• Service isolation and scanning: identify and isolate electrical, water and gas lines in chases before cutting or splitting.

Building physics: thermal, fire and acoustic performance

AAC blocks provide very good thermal performance due to the closed pore structure; in new construction, thin-bed joints reduce thermal bridges. Fire protection is a core strength of the material, which is why it is common in fire walls and service shafts. Noise insulation requires greater attention in lightweight walls; higher bulk density or multi-leaf systems improve values. Moisture management benefits from vapor-permeable exterior and interior plasters and robust detailing at parapets, reveals and connections to prevent driving rain ingress and interstitial condensation.

Typical defects and quality assurance

The most frequent issues include brittle fracture edges, pull-outs of fixings when unsuitable anchors are used, and uneven joints. In execution, the following help:

• Clean bed joints in thin-bed application, check flatness.
• Suitable fixing systems for AAC (consider tension and shear loads).
• Careful implementation of moisture protection details on external walls.
• Avoid concentrated point loads without load-spreading pads or lintels to prevent local crushing.
• Thermal bridge checks at ring beams and balcony connections to limit condensation and mold risk.

Sustainability, recycling and disposal

AAC is mineral and can be processed into granular material, for example as backfill or leveling material in defined applications. Selective deconstruction with concrete demolition shears or stone splitters and concrete splitters facilitates material separation. Regional requirements for reuse and recovery must be observed. Adhesive residues, render systems and mixed demolition waste reduce recycling quality; early separation and clean fractioning by grain size improve recovery options.

Areas of application for Darda GmbH in the context of AAC

In practical handling of AAC block there are numerous touchpoints with the tool and application segments of Darda GmbH:

• Gutting works and concrete cutting: quiet, controlled dismantling of partitions and shafts with concrete demolition shears.
• Concrete demolition and special demolition: combined use of stone splitters and concrete splitters, hydraulic wedge splitters and concrete demolition shears at transitions to reinforced concrete.
• Special demolition: work in sensitive areas where vibration and noise must be minimized.
• Confined situations such as basements and shafts where low reaction forces and compact tool geometry are advantageous.

Planning and execution tips for existing buildings

For change of use and conversions with AAC walls, early deconstruction planning is recommended. Investigations into wall build-up, anchors and any hidden reinforcement reduce surprises. A coordinated approach – pre-weakening, splitting, crushing, separating – accelerates construction logistics and increases safety.

• Define noise and dust time windows with stakeholders and coordinate logistics routes for debris removal.
• Survey and mark services in wall chases; decouple fixtures and built-ins systematically before segmental removal.
• Protect adjacent finishes with sacrificial layers and edge guards; plan intermediate storage for reusable elements.