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 Corrosion of Steel In a Reinforced Concrete Bridge
Abstract Studies were made to determine the cause of accelerated corrosion of reinforcing steel in a concrete bridge in a salt water environment. There was good reason to believe that macro-galvanic corrosion was involved. Resistivity and corrosion cell ratio charts indicate that the resistivity of concrete decreases as the deterioration of the concrete increases. The lower resistivity measurements of the concrete in the anodic areas indicated that the anodic areas could have been created by the following factors: (1) a greater moisture content in the anodic areas, and (2) a greater sea salt content in the anodic areas. Cathodic protection may offer a means of curbing corrosion but certain precautions should be taken. All available data indicate that in new installations in salt water environments, corrosion problems can be minimized by using a concrete formulation having minimum porosity and by a design having a maximum coverage of concrete over the reinforcing steel. 6.6.5.
Nitride Capacities in the CaO-base Ternary Slags at 1873K
Nitride capacities (CN=(mass%N)·PO23/4/PN21/2) in the CaO-Al2O3-MgO(ZrO2) and CaO-SiO2-MgO(TiOx) ternary slags were measured at 1873K by a gas-slag equilibration technique, using an Mo, Al2O3 or MgO crucible under controlled partial pressures of oxygen (log(PO2/atm)=-11--14) and nitrogen (PN2=0.9 atm). The CN values increased with increasing the contents of nitride former oxides. The CN values in the CaO-AlO1.5-MOx (MOx=MgO, SiO2, ZrO2, TiOx) slags at XCaO/XAlO1.5=0.4-0.7 increased in the order of MgO<SiO2<ZrO2<TiOx and those in the CaO-SiO2-MOx (MOx=MgO, AlO1.5, TiOx) slags at XCaO/XSiO2=1.0-1.5 increased in the order of MgO<AlO1.5<TiOx at a given MOx content.