Composite mortar

Composite mortar is a central element of modern fastening and deconstruction technology. It enables load‑bearing connections between steel and mineral substrates such as concrete, masonry, or natural stone. In the context of products from Darda GmbH – for example in concrete demolition and special deconstruction, in gutting and cutting, in rock excavation and tunnel construction as well as in natural stone extraction – composite mortar is used to reliably anchor anchors, post-installed reinforcement, and temporary safeguards in the structural element. In this way, work steps with concrete demolition shears or stone and concrete splitters can be specifically prepared, controlled, and secured without uncontrollably weakening the load-bearing capacity of the existing structure.

Definition: What is meant by composite mortar

Composite mortar refers to reactive resin or cementitious injection systems that bond anchor rods, threaded anchors, or reinforcing bars into a borehole with a frictional connection. The hold results from a combination of adhesion to the borehole wall, encapsulation of the steel, and micro-mechanical interlock of the mortar matrix in the substrate. Typical applications include post-installed fixings, post-installed reinforcement connections, temporary shoring and safeguards in concrete and masonry – both in uncracked and cracked concrete, depending on system and approval.

Structure and mode of action of composite mortar

Composite mortar generally consists of two components that are homogeneously mixed by a mixing nozzle during extrusion: the reactive resin with fillers and a hardener. Alternatively, cementitious, mineral systems are used. After being introduced into the cleaned borehole, the mortar envelops the anchor bar, fills pores and roughness, and cures into a dimensionally stable matrix. The characteristic load-bearing capacity arises from adhesion, cohesion (mortar strength), and mechanical interlock (keying). Load transfer can include tension, transverse tension, shear, and combined actions; design takes into account edge and spacing distances, concrete strength, borehole depth, bar diameter, as well as temperature and moisture.

Typical applications in concrete demolition, special deconstruction, and rock

Composite mortar is used wherever anchors are intended to safely and controllably transfer loads into mineral substrates – especially when components are processed with concrete demolition shears or selectively separated with stone and concrete splitters.

Post-installed reinforcement connections

During repurposing or partial deconstruction, reinforcing bars can be post-installed to modify load paths, temporarily stabilize components, or secure cut edges for processing with concrete demolition shears.

Temporary safeguards and auxiliary structures

Anchorage for suspensions, tie rods, lifelines, dust protection walls, or guide rails of cutting tools is often executed with composite mortar – for example during strip-outs, when opening slabs, or when splitting component segments with stone and concrete splitters.

Rock excavation, tunneling, and natural stone

In rock and quarries, bonded anchors are used to secure blocks, to transfer loads during controlled splitting, and as anchorage points. The combination of a precise splitting process and chemical anchoring enables a controlled joint with minimal collateral damage.

Interaction with concrete demolition shears and stone and concrete splitters

The targeted combination of anchoring and mechanical separation increases safety, precision, and efficiency in deconstruction.

• Segmented removal: Before using concrete demolition shears, anchors are installed to secure component segments or redirect loads.
• Split control: When working with stone and concrete splitters, bonded anchors can limit crack propagation or flank defined fracture lines.
• Low‑vibration methods: Chemical anchoring minimizes additional vibrations and is therefore ideal for sensitive special deconstruction in existing buildings.
• Attachment and guiding points: Load-bearing, near-edge fixings are required for hoists, slings, and guiding systems of separation and cutting technology, which can be realized with suitable composite mortars.

Material types and selection criteria

The choice of system depends on substrate, load level, installation conditions, and environmental conditions.

• Epoxy systems: High bond strengths, good resistance, suitable for heavy loads and post-installed reinforcement; longer curing times.
• Vinyl ester systems: Fast curing, wide temperature range, often approved for cracked concrete.
• Polyester systems: Economical, predominantly for uncracked concrete or masonry.
• Cementitious systems: Mineral, low-emission, advantageous for damp holes and as a fire protection option; usually with broader installation boundary conditions.

Further criteria include borehole moisture (dry, damp, water-filled), drilling method (hammer drilling, diamond drilling), concrete age, chemical exposure, temperature range, fire protection requirements, and anchoring in cracked concrete.

Planning and design

The design of bonded anchors is based on approval-relevant parameters and structural requirements. Key influencing factors are concrete compressive strength, borehole depth, bar diameter, edge and spacing distances, load and combination cases, crack widths, concrete temperature, member thickness, minimum concrete cover, installation positions (overhead/upward installation), as well as dynamic or seismic actions. For post-installed reinforcement connections, anchorage lengths, bar grades, and bond stresses must be considered. Careful planning is particularly necessary when work steps with concrete demolition shears take place simultaneously and temporary load redistributions occur.

Execution: from the borehole to curing

The load-bearing capacity of chemical connections stands and falls with execution quality. Clean, reproducible installation is therefore essential.

1. Drilling: Diameter and depth as specified; select suitable drilling methods (hammer drilling for concrete, diamond drilling for small edge distances and dimensional accuracy).
2. Borehole cleaning: At least the sequence principle blow out – brush – blow out (multiple times), adapted to the drilling method and system specifications.
3. Injection: Prepare the cartridge, discard the first extrudate, introduce the mortar bubble-free from the bottom of the borehole.
4. Setting the anchor: Insert the bar while slowly rotating, observe overfill level, withdraw the nozzle while filling.
5. Curing: Observe waiting time according to temperature; assembly and loading only after reaching the minimum hardness.
6. Documentation and control: Records of batch and mixing nozzle, ambient temperature, visual check of fill level; document tightening torque if applicable.

Curing times, temperature, and weather

Reactive resins react in a temperature-dependent manner. Low temperatures extend working and curing time, high temperatures shorten them and require faster work. Damp boreholes, standing water, or frost affect adhesion and must be evaluated on a system-specific basis. Cementitious mortars require adequate aftertreatment to avoid shrinkage and early damage. For outdoor applications, UV, moisture cycles, and chemical exposure must be considered.

Quality assurance and testing

To support planning, suitability or application tests are performed in critical cases, such as pull-off bond tests on trial boreholes. During the project, spot checks, torque checks, and pull-out tests help assess workmanship quality. Complete documentation of cartridge batches, processing temperatures, and installation times supports traceability.

Safety and health protection

When handling composite mortar, personal protective equipment, dust extraction during drilling, adequate ventilation, and skin and eye protection are important. Reactive resins can have sensitizing effects; safety data sheets must be observed. In deconstruction, low-dust and low-vibration methods should be used – an advantage of combining chemical anchoring with targeted hydraulic processing using tools such as concrete demolition shears or stone and concrete splitters from Darda GmbH.

Typical failure modes and their causes

• Low capacities or pull-out at initial loading: inadequate borehole cleaning, incorrect bore diameter, anchorage length too short.
• Anchor rotation: voids in the mortar bed, incomplete filling, loading applied too early.
• Edge breakouts: edge distances not maintained or setting and tightening torques too high.
• Temperature-related impairments: curing time not observed, processing outside the permissible temperature window.
• Crack-related reduction in load-bearing capacity: system used without suitability for cracked concrete.

Role in the deconstruction workflow: cut guidance and load management

In practice, bonded anchors are often installed before separation to guide segment loads, control fall directions, or attach protective and guiding devices. When removing sections with concrete demolition shears, segment size can thus be optimized. During controlled splitting with stone and concrete splitters, crack lines can be stabilized by flanking anchors and undesired spalling at edges can be avoided.

Sustainability and disposal

The selection of low-emission systems, low-dust drilling methods, and minimizing additional damage contribute to resource conservation. Cartridge remnants and mortar components must be collected and disposed of in accordance with the respective regulations. With cementitious systems, the mineral base can offer advantages in terms of emissions; overall, the specific application determines the environmental assessment.

Normative framework and notes

Applicable rules of technology are decisive for planning and execution. These include recognized assessment and approval procedures for anchors in concrete and masonry, specifications for the design of post-installed reinforcement connections, as well as contractual and structural requirements. Fire protection, seismic action, and edge distances must be addressed in a concept-appropriate manner on a case-by-case basis. These notes are general and do not replace project-specific planning.