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/
Joint strength of aluminum ultrasonic soldered under liquidus temperature of Sn–Zn hypereutectic solder
Abstract In order to obtain high-strength aluminum joints, ultrasonic soldering of 1070 aluminum was conducted under liquidus temperature of Sn–Zn hypereutectic solder. A device for ultrasonic soldering was assembled, which propagated ultrasonic vibrations in a direction perpendicular to joining surfaces. This device joined 1070-Al using quasi-melting Sn–Zn hypereutectic solder without using any artificial spacers. The strength of the solder joints was evaluated by tensile tests. The optimum joining conditions were determined, and the effects of solder compositions and soldering temperature on the joint strength and the solder layer thickness were examined. In this ultrasonic soldering process, the highest tensile strength was obtained for the solder joints fabricated at 220 °C for the Sn–23Zn and Sn–40Zn solder compositions. The joint strength was equivalent to that of 1070-Al heat treated at 220 °C. The sound joints were obtained at 300 °C using Sn–82Zn solder, the liquid phase volume fraction of which was theoretically only 0.24. The present work also revealed that the thickness of retained solder layer in the joint after ultrasonic soldering could be estimated. Accordingly, ultrasonic soldering under the liquidus temperature of Sn–Zn hypereutectic solder could be a spacer-free soldering method to obtain high-strength aluminum joints.