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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.

Concrete is a characteristically porous material, and whatever improvements are made in its formulation and fabrication, micropores and microvoids would always exist on their surfaces. These defects encourage the transport of aggressive agents into the body of concrete, bearing in mind that cracking, depth, and quality of cover concrete and the overall quality of concrete are the three factors that influence the penetration of these agents. Surface coatings on concrete have an important role in preserving the durability of concrete and the steel embedded in it. This paper presents test data on an acrylic-based highly elastic surface coating. The strength and elasticity of the coating, its ability to bridge cracks under static and dynamic loadings, its resistance to natural weathering, heat, oxidation, sunshine, and rain are discussed. Data are also presented on the adhesion strength of the coating to concrete substrate and its resistance to carbonation and chloride penetration. Both short- and long-term test data are presented. It is shown that a highly elastic rubber coating can provide long-term durability and stability to concrete structures, and that it can maintain its integrity, continuity, and adhesion to concrete under very aggressive environmental conditions.

The Story Bridge is a densely trafficked, important corridor over the Brisbane River. Built in the 1940s, the bridge (particularly the southern approaches) are showing signs of distress. The main span of the bridge consists of two steel cantilever trusses with a drop-in steel span. The overall length of the main span is 446 m. The southern approach spans consists of steel trusses, concrete girders, and a grillage of beams with a concrete deck, for a combined length of 515 m. There have been longstanding concerns with respect to some elements of the bridge. These are expressed most visibly by extensive cracking and spalling of the concrete. In some locations primary reinforcement is completely rusted through, leaving doubts about the safety of local areas of the bridge. Some rocker bearings appear to be partially or totally seized. The investigation involved an historical review of the design and construction details used in the bridge. Design loads were compared with modern standards. The concrete quality was investigated and the level of corrosion determined. These are reported in the context of the original specifications and details, and repair procedures recommended.

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.