Temperature reinforcement is a central detail in structural concrete construction to limit crack-related impairments caused by heating and cooling of concrete. It supplements the load-bearing reinforcement and counteracts restraint from heat of hydration, temperature gradients, and shrinkage deformations. This topic has high practical relevance for deconstruction: Dense temperature reinforcement influences how components respond to local loads and separation processes, for example when working with concrete demolition shear or hydraulic rock and concrete splitters by Darda GmbH in selective deconstruction, tunnel construction, or when opening slabs and walls.
Definition: What is meant by temperature reinforcement
Temperature reinforcement refers to the arrangement of reinforcement bars or meshes that serve not primarily for load-bearing capacity but to limit temperature- and restraint-induced cracking. It distributes restraint stresses resulting from heat of hydration, later temperature cycles, and drying shrinkage over larger areas, reduces crack width, and improves serviceability. Typical applications are large-area ground slabs, walls, slabs, tunnel linings, and massive foundations in which temperature differences and deformation restraint occur.
Background, mechanisms, and practice of temperature reinforcement
Temperature reinforcement is effective where concrete is subjected to tension due to thermal expansions and restraints of its length change. During hardening, concrete heats up due to hydration; later it cools down. If temperature gradients develop across the cross-sectional thickness or if shrinkage or temperature shortening is restrained by supports, adjacent components, or the subgrade, tensile stresses form. Without sufficient reinforcement, wide cracks occur; with suitable temperature reinforcement, fine, closely spaced cracks are formed, which improves watertightness, durability, and visual quality. In practice, design is oriented toward minimum reinforcement against restraint and the permissible crack width. The reinforcement should be arranged in near-surface zones where tensile stresses from cooling and shrinkage occur. It is often executed as reinforcement mesh on both faces or uniformly distributed bars with appropriate bar spacing. Complementary concrete technology measures include adjusted concrete temperature, suitable choices of cement and aggregates, reduced element thickness by staged pours, curing, and joint planning. For deconstruction this means: The existing temperature reinforcement holds concrete parts together even after cutting; separation and size-reduction tools must engage the reinforcement or additionally cut it. When using concrete demolition shear or rock and concrete hydraulic wedge splitters by Darda GmbH, knowledge of the location, density, and direction of the temperature reinforcement is decisive for controlled removals, minimal secondary damage, and repeatable fracture patterns.
Causes of thermally induced cracking in concrete components
Thermally induced cracks result from a combination of temperature change, gradient, and restraint. Massive cross-sections, early hardening phases, and strongly restrained situations are particularly critical.
Typical triggers
- Heat of hydration in massive members (foundations, thick walls, tunnel linings)
- Daily and annual ambient temperature cycles with temperature changes in slabs and plates
- Restraint due to rigid supports, fixity, friction on the subgrade, or adjacent building parts
- Non-uniform cooling: cold outside air acting on a warm element core
- Additional factors: wind, solar radiation, early restraint effects from the construction sequence
Consequences without appropriate measures
- Wide, uncontrolled cracks penetrating the cross-sections
- Impaired watertightness and durability (chlorides, CO₂, freeze–thaw de-icing exposure)
- Undesired crack patterns and potential usability impairments
Design concepts and practical arrangement
The design of temperature reinforcement follows the principle of crack width limitation and ensuring sufficient minimum reinforcement against restraint. In practice, simplified approaches for minimum reinforcement ratios, bar spacing, and edge zones are used.
Guidelines for reinforcement arrangement
- Reinforcement on both faces in near-surface zones of slabs and walls where tension occurs
- Uniform distribution with moderate bar diameters and small spacing to achieve fine crack networks
- Lap splices and anchorage with adequate development lengths; avoid notch effects
- Grid action in midspan and along edges, especially for large panel sizes and restrained supports
- Joint planning to limit panel sizes and reduce restrained lengths
Member-specific aspects
- Walls: arrange reinforcement through the thickness to match the expected tension side
- Slabs/ground slabs: reinforcement mesh on both faces; consider subgrade friction as restraint
- Tunnel linings: temperature gradient between rock mass and structure, ring-shaped reinforcement meshes
- Foundations/massive members: increased minimum reinforcement ratios, concreting in stages if necessary
Execution, concreting, and curing
Good execution reduces restraint peaks and supports the effectiveness of temperature reinforcement.
Concrete technology
- Adjusted cement types with reduced heat of hydration
- Provision of cooler constituents or temperature control of fresh concrete
- Staged concreting and controlled pour lengths
- Careful stripping of formwork to limit temperature gradients
Curing and protection
- Moist curing of surfaces, avoiding rapid drying
- Protection from drafts and direct solar radiation
- Temperature monitoring with embedded sensors in massive cross-sections
Relevance in deconstruction, separation, and size reduction
Temperature reinforcement significantly shapes component behavior during separation. For selecting and sequencing equipment from Darda GmbH, knowledge of reinforcement density and layout is critical to achieve controlled fractures and clean cuts.
Concrete demolition shear: gripping, crushing, shearing
- Finely distributed temperature reinforcement holds concrete together after initial breakup; “dangling” bars result that must be cut subsequently.
- With dense mesh reinforcement, a combined approach is recommended: pre-size-reduction with concrete demolition shear, followed by severing protruding bars with combination shears, multi cutters, or steel shears.
- The crack path aligns with weaker zones between reinforcement bars; smaller jaw openings and higher cutting forces are required in near-edge regions.
Rock and concrete hydraulic wedge splitters: wedge forces and crack initiation
- Split wedges generate local tensile stresses. Dense temperature reinforcement can deflect or slow crack propagation.
- Drillhole positions must be selected so that reinforcement bars are not hit directly; rebar locating beforehand minimizes disturbances of the split line.
- If crack progression is insufficient, an interplay helps: pre-sawing separation joints, splitting, cutting reinforcement, splitting again.
Hydraulic power packs and equipment combinations
- Hydraulic power packs supply concrete demolition shear and splitters with constant pressure and flow rate; using suitable hydraulic power units is important for repeatable fracture patterns.
- Equipment combinations in selective deconstruction: first split to initiate cracks, then use shear to open the cross-section, finally shears to cut the steel.
Temperature reinforcement in typical application areas
The following components and scenarios show how temperature reinforcement influences work planning and equipment use.
Concrete demolition and special deconstruction
- For large floor slabs with crack networks from temperature restraint, creating openings requires a close interplay of splitting and subsequent cutting.
- Massive retaining walls with near-edge reinforcement are opened section by section with concrete demolition shear; remaining reinforcement is separated with shears.
Gutting and cutting
- When creating openings in slabs, temperature reinforcement inhibits uncontrolled spalling; pinpoint split lines and clean shear cuts are possible when the reinforcement layout is known.
- In composite zones (e.g., adjacent steel members), shears for steel cutting follow the shearing or splitting operation.
Rock removal and tunnel construction
- In tunnel interior works, temperature gradients act between the rock mass and the inner lining; ring-shaped temperature reinforcement is common. During deconstruction or modification works, concrete demolition shear and splitters should be selected to cut the ring reinforcement in a targeted manner.
Natural stone extraction
- Here, splitting without reinforcement is the focus. However, experience from controlled crack steering is transferable, e.g., for arranging drill rows and controlling the fracture plane.
Special case
- Heat- or fire-exposed components: redistributions in reinforcement are possible; during deconstruction, expect altered steel ductility and more brittle concrete.
Planning, documentation, and quality assurance
Good preparation determines efficiency and safety when working on temperature-reinforced components.
Investigation and documentation
- Review as-built drawings and reinforcement schedules; if uncertain, use low-destructive detection
- Record member thickness, panel sizes, joints, and support conditions
- Crack mapping: direction, width, activity to assess restraint conditions
Work sequence and safety
- Clearly define the sequence splitting–shear–cut; respect load-bearing functions
- Document hydraulic power pack settings to achieve repeatable cuts
- Minimize fall and crushing hazards from spring-back reinforcement; provide retention measures
Concrete technology complements for crack minimization
Besides reinforcement, concrete technology strategies reduce crack propensity and facilitate later separation by producing a more homogeneous matrix.
- Adjusted binders and cement contents to reduce heat of hydration
- Control of fresh concrete temperature and placement times
- Targeted curing and controlled cooling
- Sensible joint and pour sequencing
Practical notes for deconstruction with tools from Darda GmbH
Temperature reinforcement is not an obstacle in deconstruction but a manageable boundary condition. Those who know its location and effect use it for controlled separation lines and predictable fracture patterns.
- Preparation: rebar locating and defining split and cut lines along presumed weaker zones
- Combination: concrete demolition shear for opening and size reduction, rock and concrete hydraulic wedge splitters for defined crack initiation, shears for separate steel processing
- Hydraulics: constant parameters of the hydraulic power packs ensure steady progress and reduce unwanted crack branching
- Section-by-section approach: small panels create lower restraint and lead to more uniform results