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.

Gunite (dry-mix shotcrete) was introduced to the construction industry in the early days of concrete technology (1911) when many new ideas and concepts were just developing. The literature indicates that what we know as wet-mix shotcrete had its start about the same time but did not receive positive acceptance until 1950. The evolution of the shotcrete process to its present status in the construction industry is tracked by definitions of the process from Gunite in 1912 to the American Railway Engineers Association (AREA) definitions of Shotcrete in early the 1930s. By 1951, the adopted the term shotcrete, making it the official generic name of the process. The definitions by ACI from that time on reflect the introduction of new ideas and equipment into the market place. The author questions whether some low velocity shotcretes are truly shotcrete or just an extension of the concrete pumping process. A brief description and evaluation, from the past to present, of shotcrete materials, applications, and testing is presented. The future of the process is discussed and two major problems posed: the improvement of applicator workmanship and the development of a rational design for most shotcrete applications.

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.

The authors had tested eight square reinforced concrete columns subjected to combined flexure and constant axial loads of 0.254 to 0.629 f'?c A?g, and the test results were reported in a previous paper. This study is a continuation of that previous study. The objective of this study is to evaluate the ductility enhancement of high-strength concrete columns achieved by effectively confining the core concrete using transverse reinforcement with high yield strength. Four test columns were constructed using concrete with compressive strength of 130 MPa, transverse reinforcement with yield strength of 408 or 873 MPa, and ordinary longitudinal reinforcement. Those columns tested under reversed cyclic lateral loads with constant axial compressive load levels of 0.343 or 0.473. Test results indicated that even for such high-strength concrete columns adequate ductility was secured by using high-strength transverse reinforcement. Based on the test results, the stress-strain model on confined concrete previously proposed by the authors was modified to be applicable not only to ordinary strength concrete but also to high-strength concrete