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.

A brief review of deterioration in concrete structures exposed to marine environment is presented. The paper also discusses problems associated with heavily deteriorated concrete piles of a harbor platform and their repair. It also concentrates on factors promoting corrosion of reinforcement in concrete piles causing cracking and spalling of concrete. Ways of assessing the degree of deterioration in concrete piles due to corrosion of steel reinforcement using various tests (visual, electrical potential, strength properties, chloride penetration, carbonation of concrete, etc.) and methods of repair are also presented. The successful method of structural repair can only be achieved by careful diagnosis and fully understanding the nature of the problem. The repair is carried out by removal of concrete from the deteriorated concrete structures.

A 17-story reinforced concrete structure with prestressed concrete floor slab, clad with an architecturally pleasing white cement and calcined stone aggregate, exhibited signs of deterioration after 30 years exposure to central London environment. The investigation was instigated after a piece of concrete spalled from a high level and crashed down. After the investigation, when the cause of the deterioration was established, recommendations were made to the client and specifications for repair were made. After the repair specialist was selected the author supervised the repair ensuring that the specifications were strictly followed. The paper describes the investigations and the rehabilitation of the structure.