Petrography as an essential complementary method in forensic assessment of concrete deterioration: Two case studies

Concrete damage is most often first assessed using traditional methods, e.g., strength testing (compressive, tensile), total porosity from water uptake, water infiltration depth, cement/aggregate ratio and chloride content. While traditional methods may produce useful results bearing clues to resolve the problem, in some cases they do not, and can even be harmful to the parties involved. This paper describes two such cases where traditional methods provided false or inadequate results, putting liability with the wrong party. Both cases illustrate that petrography is an indispensable tool in the forensic assessment of concrete. first case, a building and construction contractor was held liable for the damage to a newly built sedimentation basin, according to the results of an initial assessment “of poor quality concrete”. A second assessment using impregnation–fluorescence petrography combined with detailed geochemical analysis revealed that instead the concrete was of normal constitution and compliant with specification, and that the damage was due to the application of urea, releasing the contractor from his conviction. cond case deals with pre-fabricated foundation piles that cracked upon pile-driving. The pile-driving contractor was blamed for the damage, allegedly from too much driving energy in combination with a worn-out wooden baffle. While the compressive strength of the concrete was normal, the tensile strength was found to be less than half of the expected value. Thin section petrography revealed poor adhesion of aggregate to the surrounding paste, confirming field observations. This could be attributed to “liquefaction and water expulsion” at an early stage of production when the piles still were under the care of the manufacturer.