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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 results obtained from tests conducted on high-strength concrete columns are reported. The experimental program comprised ten axially loaded short columns and six slender columns subjected to axial compression and bending moment. The main test parameters in the case of short columns are the area and the type of lateral reinforcement, whereas the eccentricity of the axial thrust is the major variable in the slender column tests. The paper also includes methods of calculating the strengths of reinforced concrete columns made of high-strength concrete. The calculated strengths agree closely with the test values.

Prestressed concrete railroad ties are subject to repeated impact loads generated by the passage of wheel flats, and this may bring about premature failure of the ties. In an attempt to toughen the concrete matrix, prestressed concrete ties were prepared not only with plain concrete, but also with concretes containing either steel fibers or polypropylene fibers. The ties were tested both statically and using a large instrumented drop-weight impact machine. It was found that, as expected, the steel fibers, and to a lesser extent the polypropylene fibers, improved the resistance of the ties to impact loading.

During the mid-1970s, there was a boom in the construction industry in Saudi Arabia. To meet the housing requirements, and to furnish the infrastructure needed for a growing industry, construction had to be carried out at a pace unprecedented in the country's history. In the absence of guidelines, concrete specifications from other industrialized countries were used. However, when the structures started to show signs of deterioration within a short fraction of their design life, it was realized that specifications developed for temperate conditions cannot be used in this region. Field and laboratory studies carried out at King Fahd University of Petroleum and Minerals at Dhahran, Saudi Arabia, showed that concrete in this region should not only be designed for strength, but also for durability. Since permeability is one of the most important properties that control the durability of concrete, much emphasis should be given to the production of dense and impermeable concrete. This paper reports the results of an investigation carried out on a number of reinforced concrete structures exposed to underground and seawater conditions that showed serious signs of deterioration within less than 10 years after construction. The paper recommends repair procedures for the damaged structures and future practices to extend their service life.