Reduce risk, avoid programme delays and make decisions based on evidence – not assumptions.
Concrete Corrosion:
Locate the Threat Before the Structure Fails
When a concrete asset begins to crack, delaminate or spall, the structural degradation is already in its advanced stages. Visible surface defects are rarely the start of the problem; they are the final symptom. The true threat lies significantly deeper. Embedded steel reinforcement (rebar) provides the essential tensile strength of your structure, but when the chemical environment inside the concrete matrix alters, that steel begins to corrode, expand and physically tear the asset apart from the inside out.
The Invisible Onset of Structural Rot
Healthy concrete is naturally highly alkaline. This alkalinity creates a chemical passivation layer that acts as a perfect protective shield around the embedded steel. However, this internal defence is vulnerable to slow, progressive environmental attack.
Continuous water ingress acts as a transport mechanism for structural pathogens – specifically atmospheric carbon dioxide and marine or de-icing chlorides. As these elements penetrate the porous concrete substrate, they systematically neutralise the protective alkaline environment, triggering a chemical degradation cycle exactly as outlined in the technical frameworks published by the Building Research Establishment (BRE).
Breaching the Protective Cover
The speed of this internal decay depends entirely on the depth and quality of the concrete cover protecting the steel. In many legacy structures, rebar was cast with a minimal protective cover of just 25mm. Depending on the environmental exposure and the density of the original concrete mix, aggressive carbonation fronts or chloride diffusion can steadily migrate through that 25mm barrier. Once this chemical front reaches the exact depth of the steel, the passivation layer collapses and the active corrosion cycle initiates.
The Mechanics of Failure
Once initiated, the consequences are devastating. Corroding steel reinforcement expands to up to six times its original volume. This massive internal expansion exerts immense outward pressure on the surrounding concrete matrix. This stress eventually exceeds the tensile capacity of the concrete, causing it to fracture, burst and fall away.
This exposes the compromised steel directly to the elements, exponentially accelerating the rate of structural failure and demanding immediate, heavy-duty mitigation strategies that align with the global engineering standards established by AMPP.
The High Cost of Reactive Maintenance
Treating the visible symptoms of concrete degradation is a dangerous and expensive cycle. If you simply break out the spalled concrete and apply a patch repair without understanding the underlying chemical pathology, you are guaranteeing future failure.
A partial repair creates the “incipient anode effect” – a destructive chemical shift where the newly patched area is protected, but the active corrosion is rapidly accelerated in the immediately adjacent, untreated concrete.
The Strategic Imperative of Proactive Scanning
To protect capital expenditure and extend asset lifespans, commercial portfolio managers must pivot from reactive emergency repairs to predictive, data-driven asset care. Waiting for physical spalling to manifest forces you into unplanned operational downtime, emergency structural propping and vastly inflated remediation costs.
By integrating regular forensic scanning into your planned maintenance schedules, you intercept the chemical degradation cycle long before it causes mechanical failure.
Whether dealing with marine infrastructure exposed to saltwater, highway bridges subjected to de-icing salts or ageing commercial buildings suffering from deep atmospheric carbonation, guessing the extent of the internal corrosion fundamentally compromises safety and drains maintenance budgets. To engineer a permanent solution, you must know exactly where the steel is actively rusting, how fast it is corroding and precisely why the concrete matrix failed to protect it.
Mapping the Electrochemical Reality
Structural Repairs treats corrosion as an electrochemical problem requiring an empirical, data-driven diagnosis. We deploy advanced surveying techniques to map the internal health of your asset, providing a comprehensive diagnostic report that dictates the exact remediation strategy required—whether that is targeted patch repair, galvanic anodes, or fully impressed current cathodic protection.
- Electrochemical Mapping: We utilize Half-Cell Potential testing to create a topographical map of active corrosion across the entire structure. This allows us to identify steel that is actively rusting right now, even if the concrete surface above it appears perfectly sound.
- Chemical Profiling: Our technicians conduct targeted depth-drilling to extract dust samples. These are tested for chloride ion concentrations and carbonation depth, allowing us to pinpoint exactly how far the aggressive elements have penetrated toward the reinforcement layer.
- Cover Meter Surveys: We map the depth of the concrete cover protecting the rebar, identifying vulnerable areas where the steel was placed too close to the surface during the original construction phase.
Half-Cell Potential Testing
When steel reinforcement begins to corrode, the chemical reaction generates a tiny electrical current. Half-cell potential testing measures that exact electrical activity. Engineers move a reference electrode (usually a copper/copper sulphate cell) across the surface of the concrete in a structured grid pattern. A high-impedance voltmeter measures the potential difference between the internal steel and the surface electrode. If the reading drops into highly negative millivolt (mV) territory – typically past –350mV – it is a definitive mathematical guarantee that the steel beneath is actively rusting. It tells you exactly where the degradation is occurring.
Resistivity Mapping
If half-cell testing finds the rust, resistivity mapping tells you how fast it will spread. This test uses a four-probe array (known as a Wenner probe) to pass a small alternating current through the concrete to measure its electrical resistance. If the concrete is porous, damp and saturated with chlorides, electricity flows very easily. This means the electrical resistance is low. Low resistivity acts as an aggressive accelerator for the corrosion cycle.
When you overlay the two data sets, you get the complete forensic picture. You find the active corrosion cells (half-cell) sitting inside highly conductive environments (resistivity), showing you precisely where the concrete will inevitably burst next.
Corrosion Survey Technical FAQ
When concrete is poured, its high alkalinity naturally creates a “passivating” oxide layer around the steel rebar, protecting it from rust. However, over time, carbon dioxide from the atmosphere (carbonation) or chlorides (from seawater or de-icing salts) penetrate the pores of the concrete. This destroys the alkaline protection, allowing moisture and oxygen to trigger active corrosion.
Because corrosion is an electrochemical process, it generates tiny electrical voltages. A Half-Cell Potential survey uses a specialized reference electrode (often copper/copper sulphate) connected to a voltmeter and the rebar network. By sweeping this electrode across the concrete surface, we can measure these micro-voltages and map the exact locations where active corrosion is taking place beneath the surface.
Patching only addresses the symptom. If the surrounding concrete is still contaminated with chlorides or carbonation, it remains highly corrosive. Patching a single spot often shifts the electrochemical reaction to the surrounding steel, causing new spalls to erupt right next to your fresh repair within months. A survey tells us if we need to install sacrificial anodes alongside the patch to prevent this.
We apply a phenolphthalein indicator solution to a freshly exposed concrete core or drilled surface. The solution turns bright pink if the concrete is still highly alkaline (healthy) and remains colourless if the concrete has carbonated. Measuring the depth of the colourless zone tells us exactly how close the carbonation front is to the steel reinforcement.
