08 Feb Spalling concrete repair – Specialist remedial solution

Are there any consequences of untreated spalling concrete caused by corrosion of embedded steel reinforcements?

Image: Large, loose pieces of concrete fell down from the suspended slab, exposing rusting reinforcing bars. No one was injured, fortunately.

Concrete + steel = Great partners in the built environment

When concrete is reinforced with steel rods and the steel is embedded with adequate and high-quality concrete, we achieve a composite material that not only resists compression and some tensile stress, but the passive film on the surface of the steel formed by the concrete’s high pH (alkalinity) acts as a protective shield that prevents or minimises corrosion.

A reduction of the concrete’s pH by carbonation or the ingress of chlorides (salt) are the most common causes of concrete deterioration as it causes the steel’s passive film to degrade. Rust begins to form on the unprotected steel. The build-up of rust causes tensile stresses as it grows in thickness. The pressure causes the concrete to form cracks near the steel, which will lead to more extensive cracking as the rust builds up until the concrete starts to break away and exposes the corroded reinforcing steel. This is commonly called concrete spalling or “concrete cancer”.  This can affect the compressive strength and thereby reduce the bearing capacity of the structure and shorten its service life if left untreated.

Corrosion of steel-reinforced concrete is most commonly found in columns, beams and precast concrete. It can often be linked back to a lack of adequate concrete cover, and/or poor concrete quality allowing moisture-borne contamination (chlorides, sulphates, carbonates, etc.) to access the steel via cracks.

Three conditions must exist for reinforcing steel to corrode:

• The passivation of the steel must have been destroyed by chlorides or by carbonation
• The presence of moisture as an electrolyte
• The presence of oxygen

Waterstop Solutions is one of the leading companies in our areas of expertise of fixing leaking buildings and concrete structures.

QBCC Licence Number 1162603 – Classes: Concreting and Waterproofing

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Good maintenance begins with a proactive approach to maintain, keep, preserve and protect a building.