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.
TECHNIQUES FOR EVALUATING REINFORCED CONCRETE BRIDGE DECKS
Premature deterioration of reinforced concrete bridge decks has become a serious nationwaide problem. Although a solution for the deterioration problem has not been found, there are several techniques available to identify the areas of concrete deterioration. The major cause of deterioration is discussed and each evaluation technique is described. The results of a corrosion survey of 473 bridge decks and the interim results of a concrete cover survey are described. /Author/
INVESTIGATION OF CHLORIDE MIGRATION IN REINFORCED CONCRETE UNDER APPLICATION OF CATHODIC PROTECTION
This project was initiated to examine the mobility of the chloride ion in concrete under cathodic protection and to discover whether long term application reduces the chloride ion content in the concrete surrounding the reinforcing steel. The effect of power interruptions in these systems, the rate of recovery from them, and the possibility that a minimal current density could maintain an established cathodic protection system were other factors examined. The study found evidence of chloride migration in reinforced concrete slabs under cathodic protection at an elevated current density of 50 ma/square metre. For concrete protected at a more typical current density of 10 ma/square metre, no chloride movement was detected over the duration of the tests (469 days). It was estimated that approximately 4% of the current flowing through a system under cathodic protection was transported by chloride ions. Upon removal of the cathodic protection from a slab in which a chloride concentration profile was well characterized and which increased with distance from the rebar, it was found that a significant amount of chloride ions migrated back toward the rebar over a six month period. Similarly, upon reduction of cathodic protection current density from 50 ma/square metre to 1 ma/square metre the same effect was observed. (TRRL)