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.
CORROSION MONITORING OF STEEL IN CONCRETE - THEORY AND PRACTICE. CORROSION OF REINFORCEMENT IN CONCRETE. PAPERS PRESENTED AT THE THIRD INTERNATIONAL SYMPOSIUM ON "CORROSION OF REINFORCEMENT IN CONCRETE CONSTRUCTION", BELFRY HOTEL, WISHAW, WARWICKSHIRE, MAY 21-24, 1990
Maintenance and planning of the restoration work on reinforced concrete structures need a rapid, non-destructive inspection technique that detects corrosion at an early stage. In this paper the results of potential surveys on several bridge decks of the Swiss highways, realized with a new computer controlled eight-wheel measurement system, are presented. It is clearly shown that a fixed potential value (as proposed in ASTM C 876-80) for the identification and location of active corrosion of steel in concrete does not exist. A very rapid new technique using galvanostatic pulse measurements was tested successfully on site. It gives clear, unambiguous results on the corrosion state of the rebars when half-cell potentials are uncertain. In addition, the concrete resistivity and the corrosion rate of the rebars may be estimated simultaneously.(A) (This paper was also published in volume 3 of "UK corrosion '88...." under the title "Potential mapping of Steel in Concrete". See IRRD 827578). For the covering abstract of the conference see IRRD 831449.
Migration of ions in concrete due to cathodic protection current
Abstract Four constant current densities of 32.3, 108, 215 and 538 ma/m 2 (03, 10, 20 and 50 ma/ft 2 ) at the steel surface area were used in the test program which also included chloride content of concrete as the second variable. These four current densities were maintained in steel of reinforced concrete specimens for an activation period of 14 months. At the end of the activation period, concrete powder samples were obtained from three locations of a particular specimen; near the steel, near the anode and the midpoint of steel and anode. These samples were then analyzed for Cl − , Na + , K + , Ca ++ and Mg ++ ion concentrations. It is observed that cathodic protection (CP) current drives away Cl − ions from near the steel to a short distance away. Due to the negative polarity of steel in a cathodically protected reinforced concrete structure, Na + , K + , and Ca ++ ions from the concrete pore solutions get accumulated near the steel surface. K + ions migrate towards the steel surface at a higher percentage when compared with the migrations of other cations. The effect of CP current on the migration of Mg ++ ions towards the steel in reinforced concrete specimen is not clear from the results obtained in the test program.