Repair, Rehabilitation, and Forensic Evaluation
This domain tests diagnosis and repair strategy: how to survey a deteriorated structure, how to select a repair compatible with the substrate, and how to build a defensible root-cause argument rather than a plausible story.
Condition survey
Use a cover meter for reinforcement depth, half-cell potential per ASTM C876 (readings more negative than about minus 350 mV against a copper-copper sulfate electrode indicate high corrosion probability), phenolphthalein to map carbonation depth, chloride profiles by ASTM C1218, ultrasonic pulse velocity, ground-penetrating radar and petrography per ASTM C856.
Repair principles
Remove unsound concrete to a sound substrate, square-cut the patch edges, clean and profile the surface, and use a repair material with compatible modulus, shrinkage and thermal expansion. Provide a bond coat where specified. Patching chloride-contaminated but otherwise sound concrete can create incipient anodes at the patch boundary. Other options include shotcrete, fiber-reinforced polymer strengthening per ACI 440, and cathodic protection or electrochemical chloride extraction.
Forensic method
Define the failure precisely, gather physical evidence with documented chain of custody, generate competing hypotheses, and test them against the evidence. Separate the mechanism from the root cause and from contributing factors.
Worked example
Half-cell readings of minus 420 mV near a spalled beam end, with carbonation measured at only 5 mm and chloride at 0.4 percent by mass of cement at bar depth, point to chloride-induced corrosion, not carbonation, so a barrier coating alone will not solve it.
Traps
Concluding from one test; patching without treating the surrounding contaminated concrete; using a stiff, high-modulus patch on a flexible substrate; painting over a damp or contaminated surface.