What are Expansive cracks?
Expansive cracks in concrete refer to cracks caused by internal expansive reactions, such as Alkali-Aggregate Reaction (AAR) or Internal Sulphate Attack (ISA) occurring over time.
These cracks typically manifest as distributed map cracking, where the concrete breaks up internally, leading to loss of concrete strength and is characterized by the appearance of gels or wetness stains exuding from the concrete.
How do Expansive cracks damage concrete structures?
Expansive cracks damage concrete structures by compromising their integrity and strength from within. Expansive forces are created through chemical processes such as Alkali Aggregate Reaction and Internal Sulphate Attack or by the expansion of freezing water during freeze/ thaw cycles.
Most commonly map cracks form from chemical expansion, leading to pop outs, scaling etc. and this internal break-up of concrete weakens its structural integrity, resulting in decreased load-bearing capacity. Cracks caused by freeze-thaw cycles are closely spaced and parallel to transverse and longitudinal joints; later multiplying outward toward the centre of an element, further exacerbating the damage. As a result, the structural integrity of the concrete is compromised, leading to potential safety hazards and the need for costly repairs or replacements
What causes Expansive cracks?
Delayed Ettringite Formation.
Reactive aggregates.
High alkali cements.
Inadequate concrete mix design.
How can I identify Expansive cracks in concrete structures?
Visual survey | Non-destructive testing | Destructive testing |
How can I repair Expansive cracks in concrete structures?
The repair strategy depends on the particular circumstances, namely the residual expansive potential in the concrete and may involve one or more of the following techniques to repair.
For chemical expansion such as Alkali Aggregate Reaction or Internal Sulphate attack it must be determined that the expansive reaction has stopped before repair mechanisms such as Concrete replacement; Jacketing; Concrete Impregnation and Concrete Coating are employed.
Physical expansion processes such as Freeze/ Thaw do not have the same issues and as such repair methods such as Concrete replacement; Concrete Impregnation or Concrete Coating can be used as soon as the problem is identified.