The critical chloride content – determination at structures and the influence on service life
The reliable determination of the corrosion probability at reinforced concrete structures is one of the major challenges in engineering in our time. Until today, the assessment of corrosion probability is based on the measurement of chloride profiles at structures. These profiles are compared to fixed threshold values, the critical chloride content Ccrit. Due to the lack of an applicable test method, this Ccrit is defined in codes for all structures with marginal possibilities for adjustment. Therefore, substantial, structural dependent parameters are neglected; the results of the condition assessment remain experience‐based guidelines. The test method, described in this article, enables the determination of structural dependent Ccrit. 150 mm drilling cores are taken from structures containing one centrally located reinforcing steel, which is not yet corroding. The drilling cores are exposed to a chloride solution in the lab. At corrosion initiation, Ccrit can be determined as statistical distribution.
With a large number of specimens, we established a database of Ccrit. This database shows clear differences of the Ccrit of several structures: The values are partially below, partially above the Ccrit given in Codes. With those values, remaining service life can be calculated structure dependent. In case of a lower specific Ccrit, maintenance work can be conducted, before the costs increase due to heavy corrosion damage. In case of a higher Ccrit, maintenance work can be postponed without increasing costs and still guaranteeing the structural safety.