Prepared by B. Elsener with contributions
Corrosion of steel in concrete is one of the major problems with respect to the durability of reinforced concrete structures. The majority of concrete structures perform well even after a long period of use in normal environments. However, there are various reinforced concrete structures important for our infrastructure, especially bridges and buildings, which exhibit premature damage due to environmental actions (EN 206). In contrast to mechanical actions (as load, wind, etc.) the environmental actions are not reversible and accumulate hazardous components (as e.g. chloride ions) in the concrete. A high percentage of the damages is caused by insufficient planning, wrong estimation of the severity of environmental actions and by bad workmanship and thus many of these structures need to be repaired after a short service life. In most industrial countries, repair and restoration of reinforced concrete structures today is nearly as important as new constructions. Due to the importance of the problem, RILEM set up an initial committee on reinforcing steel corrosion in 1960. A second committee related to the problem, TC 60-CSC ‘Corrosion of Steel in Concrete’, was established in 1980, presenting a state-of-the-art report in 1988 on the generally agreed knowledge about the processes causing corrosion and the corrosion mechanism themselves. RILEM TC-124 on Strategies for the Repair of Concrete Structures Damaged by Steel Corrosion published a draft recommendation in 1994, where the importance of condition assessment has been pointed out as the first step in the repair process. To ensure a sound decision on the type of repair work, it is essential to get first of all a thorough assessment of the condition of the structure, including the evaluation of: cause of damage or loss of protection degree and amount of damage expected progress of damage with time effect of damage on structural behaviour and serviceability. The acquisition of reliable information on level and rate of deterioration is done during regular main inspections relying on visual examination of the whole structure. If no reliable conclusion on the state of the structure or part of it can be obtained, an additional inspection (verification) including non-destructive testing has to be performed until the cause of damage is clearly identified. The text presented hereafter is a draft for general consideration. Comments should be sent to the TC Chairlady: Dr. Carmen Andrade, CSIC Instituto de Ciencias de la Construccion "Eduardo Torroja", Serrano Galvache s/n Aptdo 19.002, 28033 Madrid, Spain; Tel.: +34 1 302 04 40; Fax: +34 1 302 07 00; Email: andrade@ietcc.csic.es, by 31 December 2003.
The electrochemical removal of chlorides from reinforced concrete
Abstract Results of a 2-year field study performed in Switzerland to evaluate the process and to obtain information on the efficiency of electrochemical chloride removal as a restoration technique for chloride contaminated concrete are presented. It is shown that about 50% of the initial chloride content is removed within 8 weeks (ca 5 × 106 C m−2). In the treated zones of the structure the half-cell potentials became more positive by about 80–100 mV. A comparison with the theoretical efficiency for chloride removal, calculated from the transference number of chloride ions, show that mainly the free chlorides in the pore solution of the concrete are removed. Due to the slow chemical equilibrium between bound and free chlorides, a second treatment after several months also removes originally bound chlorides. For severe and inhomogeneous chloride contamination local zones with active rebars and high chloride content may remain after the treatment.
Migrating Corrosion Inhibitor Blend for Reinforced Concrete: Part 1—Prevention of Corrosion
Abstract The efficiency of a migrating corrosion inhibitor in preventing corrosion of mild steel was investigated in saturated calcium hydroxide (Ca[OH]2) solutions and in mortar. The protective ef...