KNOWLEDGE · CRACKS AND DIAGNOSIS

Concrete cracking: assessment before repair

A crack is evidence of a process. Before selecting a resin, establish what opened it, whether it is still moving and what function you expect from the repair.

Assessment Drawing explanation Selection and next step

Overview of concrete damage and cracking patterns — Fig.1.

From crack appearance to its cause

Cracks in two similar walls may look almost identical yet require different action. In one, they developed as young concrete cooled; in the other, support is still changing. Matching a photograph to a diagram alone does not determine whether sealing is sufficient, structural repair is needed or the cause of damage must first be stopped.

Start with a map: mark crack location, direction, branching and width, delamination, efflorescence and discharge points. Add the date, temperature and loading condition. Keep consistent labels so subsequent inspections describe the same locations. If both sides of the element are accessible, compare the crack paths; do not assume the surface trace represents a straight plane deeper inside.

READING THE CROSS-SECTION

What does the diagram show?

The drawing compares different cracking patterns in concrete elements. Damage position and shape provide clues to the mechanism but do not replace the element's history, activity measurements and structural assessment.

1–3 · Plastic settlement

Uneven settlement of fresh concrete. Cracks may develop near reinforcement in the first hours after placement.

4–6 · Plastic shrinkage

Rapid water evaporation from fresh concrete creates tensile stresses. An irregular crack pattern appears on the surface.

7–8 · Thermal contraction

Cooling and temperature differences between the inside and surface of an element cause deformation and stresses. This mechanism is distinct from drying.

9 · Long-term shrinkage

Gradual moisture loss over subsequent months or years causes concrete to shorten. Crack extent depends, among other factors, on restraint of the element's deformation.

10–11 · Fine surface shrinkage cracks

A fine crack network associated with moisture differences between the surface layer and concrete interior. It should not automatically be equated with a crack passing through the full cross-section.

12–13 · Reinforcement corrosion

Corrosion products increase in volume and exert pressure on surrounding concrete. Cracks along bars may be accompanied by rust staining and cover delamination.

14 · Alkali–silica reaction (ASR)

Expansive gel formed by reactions between concrete constituents causes internal stresses and cracking. Identifying this process requires testing, not merely comparing a photograph with a drawing.

History helps distinguish mechanisms

First hours and days

Cracks near reinforcement or thickness changes may relate to settlement of fresh concrete. Irregular cracking of an exposed surface may accompany rapid water evaporation. Check concreting, curing, weather conditions and when the damage first appeared.

Cooling and drying

Thermal deformation and drying shrinkage have different causes, but both can cause cracks when the element cannot shorten freely. Look for connections with casting stages, element length and restraint locations.

Loading and support

Changed loads, deflection or uneven settlement require assessment of structural behaviour. Resin can fill the fissure but does not remove the cause of changed support or overloading.

Corrosion and expansive processes

Rust staining, detached cover or network cracking justify further testing. Reinforcement corrosion and expansive reactions cannot be diagnosed solely from surface line patterns; filling a crack will not stop their cause.

One measurement does not describe activity

A crack dry on inspection day may carry water after the groundwater level changes. A crack stationary at one temperature may move in daily or seasonal cycles. Plan crack width and possible displacement measurements to cover relevant service conditions. For cracks following load changes, compare measurements with the history of that change.

Surface width determines neither depth nor void volume. If necessary, supplement assessment with investigation of the cross-section, concrete and reinforcement. The investigation scope should match the element's function and the consequences of damage.

Record the repair function before the product name

Sealing must limit water transport and remain watertight under the expected crack behaviour. Force-transferring repair must provide specified interaction between parts of the element and requires a design and appropriate acceptance. Flexible material and rigid epoxy bonding address different needs.

If the cause remains active, establish how to remove it or accommodate it in the design. Where a bearing capacity problem is suspected, structural engineer assessment is needed before defining the injection scope. Only after classification should you select crack access, surface sealing and an injection trial.

What should the diagnosis produce?

For each zone, prepare the probable cause and basis for diagnosis, activity assessment, water conditions, repair objective and acceptance criterion. Also specify what will be remeasured and when. This prevents disappearance of a leak from being mistaken for proof of restored load-bearing capacity.

Acceptance relates to the established objective. For sealing, it includes checking the zone and adjacent water paths under representative conditions. For structural repair, the design defines how filling and material interaction are confirmed.

RESINBAU SELECTION

Calculate what you know

CALCULATORCrack drilling geometry →

Use after assessing the cross-section; the model does not diagnose the cause or actual crack depth.

Next step

Move from diagnosis to the filling method.

Discuss your project conditions

Prepare a cross-section, a description of water and movement, and results of previous trials. ResinBau helps select the material and application method.

Discuss your project / technical selection ↗