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.

A major rehabilitation of the reinforced concrete approach viaduct to the Pattullo Bridge has been successfully completed over the last nine years. A condition inspection revealed that extensive cracking had taken place over the years,especially at the bridge girder ends due mainly to frozen bearings. A program of bearing replacement was carried out at all girder ends along with seismic improvements and general concrete repairs. An elaborate falsework system was designed which was easily adaptable to the varying geometry along the viaduct. Load transfer to the falsework to implement the rehabilitation was achieved using a hydraulic jacking system. The work was carried out in a series of six contracts and the project was completed without any bridge traffic closures during the assignment.

An intense fire in the antioxidant plant of a chemical factory near Bombay caused extensive damage to the reinforced concrete frame of the building as well as to the flooring, equipment, fixtures, and fittings. Consultants were appointed to investigate the damaged structure and later to design and supervise the rehabilitation work. After the preliminary investigation, the consultants decided that it was not necessary to demolish the structure, as long as it was possible to restore the structural members at a reasonable cost and within a short time span. In addition to visual inspection and sounding, extensive nondestructive tests were conducted to determine the extent of damage and the residual strength of the important load-carrying members of the structures. The findings of the investigations were analyzed and the restoration system was designed by the consultants. The paper outlines the considerations that led to restoration of the structure in preference to demolition, the details of investigations, the analysis of the findings, and the successful rehabilitation techniques that followed.

The crest of Kakabeka Falls, a major tourist attraction near Thunder Bay, Ontario, had changed rapidly within 15 years. Geotechnical evaluation had concluded that, due to the geometry of the rock formation, there was little continuous cap-rock beyond the crest of the falls. Undercutting by water and subsequent ice jacking and freeze-thaw action was eroding the remaining cap-rock. Without prompt remedial work, the falls would degenerate to rapids over 50 years. Rapid recession of the falls also threatened the foundations of two bridges. In 1988 and 1989, remedial works were undertaken to stabilize the erosion process and improve the appearance of the falls. Concrete mixes were designed using powdered color dyes to duplicate the color and appearance of the reddish brown cap-rock and black hales. The crest of the falls was reconstructed incorporating a weir which spread the water flow evenly across the width of the falls. Special formwork and hand-finishing techniques were used to texture the concrete surface to match the existing rock. Two years in planning and eight weeks in construction, the project successfully restored the falls to its former beauty.

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.