When Concrete Fails
Concrete is New Zealand’s most widely used structural material — in foundations, frames, floors, bridges, retaining walls, and infrastructure — and most of it performs well for its intended life. But concrete can deteriorate, develop defects, or suffer damage that reduces its performance and requires remediation. Understanding the causes of concrete deterioration, the assessment methods used to evaluate it, and the repair systems available to address it is specialist knowledge with a significant market in New Zealand’s aging built environment.
Concrete deterioration in New Zealand most commonly results from: carbonation and steel reinforcement corrosion (particularly in older structures in aggressive environments); alkali-silica reaction (ASR) in some aggregate combinations; freeze-thaw damage in the South Island; mechanical damage from impact or overload; and inadequate initial cover depth or concrete quality that has allowed early onset of reinforcement corrosion.
Assessment Before Repair
Effective concrete repair starts with understanding the cause and extent of the deterioration. Patch repairs that address the visible symptoms without dealing with the underlying cause — active reinforcement corrosion, for example — will fail. A concrete assessment by a specialist engineer, using a combination of visual inspection, cover depth measurement, carbonation depth testing, half-cell potential surveys, and core extraction for laboratory analysis, provides the information needed to design a durable repair.
Repair Systems
Concrete repair systems range from cementitious mortars for localised patch repair through to cathodic protection systems for large-scale reinforcement corrosion management. The selection of repair materials needs to be compatible with the parent concrete — materials with very different modulus or thermal expansion characteristics can cause repair failures through differential movement. Repair material manufacturers’ technical support is an important resource for specifying and installing effective concrete repairs.