International Concrete Abstracts Portal

SP128 Leading world experts met in Hong Kong to participate in The ACI conference on Evaluation and Rehabilitation of Concrete Structures and Innovations and Design. The specific purpose of the Conference was to disseminate technical information on emerging concrete technology in the Pacific rim region. You can review the results of that timely event in a two volume document comprised of 90 technical papers. Volume I contains paper dealing with materials. Topics include: high elastic surface coatings, concrete deterioration on high chloride and sulfate environment, nondestructive testing, impact-echo technique, fiber reinforcement, injectable cementitious materials, and case studies. Volume II is comprised of papers pertaining to design aspects. Topics include: concrete for offshore structures, performance of structural repairs, design of high-strength and reinforced concrete structures, design of beams and columns, and case studies.order.

The Hong Kong Housing Authority's annual maintenance budget currently runs at around US$140m, approximately US$13m of which is expended on patch repairs to spalled and delaminated concrete, totalling 65,000 mý per annum. In recent years, a large number of different proprietary brands of repair material, both prebagged and site-mixed, have been used and new materials are continually being introduced. Two basic problems have been encountered: determining the suitability of materials for various applications, and controlling the preparation and application of repair mortars. Manufacturers of proprietary materials tend to use different tests and standards against which to evaluate the performance of their products and, with regard to the assessment of the performance and quality of repairs as applied, there are presently very few internationally accepted testing standards. The Housing Department has, therefore, developed its own series of tests and administrative procedures for classifying concrete repair mortars and controlling the quality of repairs. These include prequalification tests and routine quality control tests required to be undertaken by materials suppliers, the establishment of an approved list of materials, field trials undertaken at the commencement of repair contracts, and quality control tests undertaken during the contracts. This paper describes the background to and development of these procedures. Avenues for further development are also discussed.

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 paper briefly introduces experience with rotating machinery grouting, and the perceived need for a high-temperature service polymer-based grout material. It discusses design and handling parameters, and the development of a product that cures at ambient temperatures, without appreciable shrinkage, and has a compressive strength at 150 C of more than 40 MPa.