International Concrete Abstracts Portal

The US Army Corps of Engineers recently completed the Repair, Evaluation, Maintenance, and Rehabilitation (REMR) Re-search Program. The primary objective of this six-year, $35- million research effort was to develop effective and affordable technology for maintaining and extending the service life of existing Corps civil works structures. Savings of over $40 million, or more than four times the funding, have already been reported from the use of technology developed in the Concrete portion of REMR. Development and application of some of the technology which resulted in savings are described herein. Examples of this technology include (a) identification of materials and methods which allow in situ repair of deteriorated mass concrete as an alternative to conventional concrete removal and replacement, (b) development of concrete mixtures containing antiwashout admixtures which have been used successfully in underwater repairs without the usual tremie seal, (c) design and installation of a precast concrete stay-in-place forming system for lock wall rehabilitation, including concepts for installation of the system in an operational lock, (d) development of stability criteria that eliminate the need for expensive structural rehabil-itation of aging concrete gravity structures, (e) development of a new procedure for anchor embedment in hardened concrete under submerged conditions, and (f) identification of repair materials with a cavitation resistance more than 25 times greater than conventional concrete with 9,000 psi (62 MPa) compressive strength.

An investigation was carried out to evaluate the effectiveness of epoxy systems injected into cracks in concrete in order to repair damaged concrete structures. It was found that the usual parameters (viscosity, elastic modulus) characterizing epoxy system are not sufficient for such an evaluation, since concrete microstructure and crack width are determinant factors. Successful1 injection into larger macrocracks (>0,8 mm) is independent of the epoxy system viscosity. However, for narrower cracks (< O,3 mm), the effectiveness of the injection strongly depends on the viscosity of the epoxy system, so that a threshold value of viscosity can be determined for each microcrack width. The injection of epoxy systems into cracks of porous concretes causes, in addition to the crack filling, an impregnation of the material surrounding the crack area. This impregnation causes a strength increase, which is higher for more porous concretes and higher epoxy system viscosity. The mechanical behaviour of injected concretes do not depend significantly on the mechanical properties of the epoxy system, whereas the rheological properties of the epoxy system can affect the performances of injected concretes.

Recently, the quality of the surface layer of concrete has been recognized as an important index to relate the durability of concrete structures. However, an appropriate assessing method has not yet been achieved. The assessment of the change in the quality of the surface layer should be made from the viewpoint of not only the mechanical property but also other physical and chemical properties, such as pore structure, carbonation and so on. Attaching importance to the simplicity of tests on site, the authors have proposed that the pull-off tensile strength by the pull-off method is applicable to the former and the recovering speed in the rapid air permeability test to the latter. This study describes the results of tests on the surface layer of concrete using specimens exposed in both inland and seashore locations in the cold district of Japan. Then, the capabilities of two specific tests are examined to assess the properties of the surface layer of concrete due to weathering and other environmental attacks.

The half-cell potential method, one of the electrochemical techniques, is very simple and possibly the most practical method as the nondestructive inspection system for steel corrosion in concrete. However, at present, this method has been regarded as an inspection only for qualitative information on corrosion. In this study, the effectiveness of the half-cell potential method on the corrosion inspection system for steel in concrete was theoretically and experimentally analyzed, and the following results were obtained: 1) configuration of the potential distribution on the structure is more important than the value of potential itself for acquiring quantitative corrosion information on steel in concrete structures, 2) progressive corrosion area of steel reinforcement can be estimated by finding the inflection point of potential distribution curve, and 3) if the electric resistivity of concrete is measured at the same time as the potential, approximate corrosion weight loss of reinforcement can be estimated by using both the potential and this resistivity distribution data.

Steel reinforcement embedded in concrete is normally passivated in its alkaline environment. In the presence of chlorides, however, the passivating layer is destroyed and the reinforcing bar corrodes, leading to concrete cracking and spalling. Several concrete rehabilitation techniques are available, of which only the cathodic protection (CP) of reinforcing bars was found to stop corrosion regardless of the chloride content of concrete. The CP system consists of reinforcing bars (cathode) connected to the negative terminal of a DC power supply, the positive output of which goes to an anode usually embedded in concrete. This paper describes some properties and applications of a proprietary activated titanium anode mesh and ribbon to a variety of old and new concrete structures: bridges, tunnels, buildings, wharves, piers, offshore platforms. Since its commercial introduction in 1985, 290,000 mý of this anode mesh has been or is being installed all over the world, whereas from 1987 the anode ribbon has been or is being applied to 29,000 mý of concrete surface. The paper addresses also the design and various installation techniques of anodes, as well as the testing, commissioning, and cost of the CP system.