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.

Definition: What is meant by 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. The resulting air pores, finely distributed throughout the matrix, lower the bulk density and improve 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.

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.

Typical characteristic values

• Bulk density classes: approx. 0.30–0.70 kg/dm³ (typical on site 0.35–0.60).
• Compressive strength classes: about 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.

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 ~1–3 mm), which reduces thermal bridges. 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.

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.

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.

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.

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. For precise adjustments, low-dust working with dust extraction is recommended.

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.

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:

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.

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.

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.

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. This coordinated sequence is common in concrete demolition and special demolition.

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.

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.

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.

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.

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.

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.