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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.

The influence of mix constituents on the quality of concrete is discussed. Results demonstrate that the assessment of concrete performance based on the traditional parameters such as water-cement ratio and 28-day strength may be misleading. One way to insure a durable structure is to specify concrete by performance criteria. This would overcome not only the influence of constituents, but would also place emphasis on proper curing. For the protection of reinforcement against corrosion, performance criteria based on carbonation and water sorptivity are suggested.

This paper presents the characteristics of the surface-layer strength of concrete produced using a special curing sheet to improve the surface layer. The curing sheet is attached to the interior of the forms and has the ability to absorb water from the concrete surface and to retain the absorbed water for curing. The surface layer strength was measured by a pullout test that was carried out by modifying the Michaelis test machine and using truncated conical steel cones embedded in the concrete. The 14-day surface layer strength obtained by using the special curing sheet increased by 1.2 to 1.5 times of that obtained without using the sheet. The improved strength is attributed to the lowering of the water cement ratio in the surface layers produced by using the sheet. After freeze-thaw tests, the surface layer strength of air-entrained concrete showed less decrease independent of the use of special curing sheet. The surface layer strength might be a useful index for the evaluation of the quality of the surface layer of concrete.

Repair and strengthening practice is based mainly on intuition, and reliable experimental data available on the repaired/strengthened reinforced concrete structural member behavior are very limited. However, the subject has recently started to receive researchers' attention, and a few experimental studies are being carried out in various European and North American countries. Current research activities in this field at the Middle East Technical University and Gazi University, Ankara, Turkey, are briefly introduced. The projects reviewed are: 1) jacketed column behavior under uniaxial load or combined axial load and reversed cyclic bending; 2) behavior of beams strengthened for flexure under monotonic, repeated, and reversed cyclic loading as well as beam strengthening by epoxy glued steel plates; 3) slab repair and strengthening; 4) system behavior improvement by introducing either cast-in-place reinforced concrete infills or masonry infills; 5) epoxy anchorage of new steel into the existing concrete. Results obtained from the test series already completed are briefly reported, and the other series in progress are briefly introduced.

As the results of CEN/PC directives in 1986 and subsequent decisions, the work of CEN/TC 104 "Concrete Performance, Protection, Placing and Compliance Criteria," was extended to cover standardization work on admixtures for concrete (TC 104/WG 3) fly ash for concrete (TC 104/WG 4), mixing water for concrete (TC 104/WG 5), grouts for prestressing tendons (TC 104/WG 6), and sheaths for prestressing tendons (TC-104WC 7). In June 1989, TC 104/WG 8, protection and repair of concrete structures, was formed.