International Concrete Abstracts Portal

Mr. Landau graduated from Harvard Business School and held positions of major responsibility in the textile field in Germany, Belgium, Canada and the United States. With a background in the global fiber industry, specializing in polypropylene since 1971 Landau introduced the U.S. product, Fibermesh, into the world-wide construction market. Since 1983, he has traveled extensively developing a sales and engineering organization supplying polypropylene fibers for use in concrete. Landau has participated as a speaker in many National and several International Conferences, including the July, 1984 Conference in Rio de Janeiro, Brazil, Rilem Conference in Sheffield, England in July, 1985, XIII Bienniel Conference in Brisbane, Australia, 1987, and the Concrete Society Conference in Hong Kong, July 1987.

In situ nondestructive evaluation techniques for estimating rebar corrosion, crack depth, deterioration due to microfracturing, and kinematics of crack nucleation in concrete structures are investigated. For corrosion monitoring, a half-cell potential technique is improved. Distribution of electrical potential on rebar surface is analytically determined from surface observation of concrete, based on a computer-aided CSM (charge simulation method) procedure. The depth of surface crack is evaluated by the ultrasonic spectroscopy. A reference curve determined from the ratio of peak frequencies is applicable to not only plain concrete but also reinforced concrete (RC) members. The amount of microcracks associated with the deterio-ration is estimated from AE (acoustic emission) activity during a uniaxial compression test of core sample. The occurrence of AE events is quantitatively analyzed on the basis of the rate process theory. A source inversion analysis of AE waveform is developed to obtain information on location, type, and orienta- ion of crack nucleation. Basic results of the above techniques are summarized and in situ applications are discussed.

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.

The assessment of reinforcement corrosion in concrete structures before visible cracking and rust stains occur will enable the engineer to take cost-effective and timely remedial action. While half-cell potential mapping techniques have been used very successfully to indicate the location of active corrosion, this method provides no information on the severity of the corrosion rate and hence the scale of the problem. The linear polarization technique provides a means of assessing directly the rate of active corrosion by measuring the response of the reinforcement to a small perturbative signal. The method has generally been restricted to laboratory studies, due to difficulties in evaluating the region of influence of the test by allowing for a relatively high concrete resistance and in the availability of field instrumentation. This paper reports on the development of unique programmable polarization equipment, enabling corrosion rate measurements to be easily collected and stored on site. The results of laboratory studies on control specimens are compared with those taken from structures in aggressive corrosion environments. Guidance is given on the interpretation of linear polarization results from durability studies for those unfamiliar with the technique.

Corrosion of steel reinforcement in concrete is one of the major problems with respect to the durability of reinforced concrete structures. Chloride ions are considered to be the major causes of premature corrosion of steel reinforcements. A test building was constructed in 1984 and has been exposed to a marine environment under the subtropical weather of Okinawa, Japan, for 6 years. This paper presents the evaluation on this test building, where nondestructive testing has been emphasized. Using a currently developed corrosion diagnosis system, the electrochemical characteristics, such as corrosion potential, polarization resistance, and concrete resistance, are measured. These characteristics are used to evaluate corrosion of the reinforcements, and the significance of this research is to enable one to evaluate corrosion of the reinforcements more quantitatively.