International Concrete Abstracts Portal

The pulse-echo method, the impulse-radar method, and the resonant-frequency test technique will provide accurate data relative to the physical and mechanical characteristics of in situ concrete and embedded reinforcement steel. These methods can be applied in combination or individually, dependent on the project application. Engineering data obtained from nondestructive (NDT) test procedures and enhanced by computer-analysis techniques are used in a wide variety of field inspection applications.

The half-cell potential method, one of the electrochemical techniques, is very simple and possibly the most practical method as the nondestructive inspection system for steel corrosion in concrete. However, at present, this method has been regarded as an inspection only for qualitative information on corrosion. In this study, the effectiveness of the half-cell potential method on the corrosion inspection system for steel in concrete was theoretically and experimentally analyzed, and the following results were obtained: 1) configuration of the potential distribution on the structure is more important than the value of potential itself for acquiring quantitative corrosion information on steel in concrete structures, 2) progressive corrosion area of steel reinforcement can be estimated by finding the inflection point of potential distribution curve, and 3) if the electric resistivity of concrete is measured at the same time as the potential, approximate corrosion weight loss of reinforcement can be estimated by using both the potential and this resistivity distribution data.

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.

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.

A detailed investigation was made to study the shear transfer between precast prestressed beams and in situ concrete in a relatively new method of construction of continuous bridge decks where the ends of precast beams are connected to an integral in situ crosshead away from the supports. The main advantages of this method are: Increasing the span length, standardization of the beams, elimination of the deep support girder, obtaining full continuity for the dead and live loads, and possibility for using straight beams in skew and curved bridges. The prestressed beam used in the investigation was an inverted T-section, and it was concluded that: 1) The shear force is transferred from a small length at the end of the beam. 2) The in situ concrete nibs can take this shear force without stirrups. 3) There is no need either to project all the bars into the in situ concrete or to prestress the connection transversely. 4) The shape of top flanges of the prestressed beam had a significant effect on the shear transfer capacity of the connection. 5) For the beams without top flanges, the shear strength of the connection can be modified by using transverse prestressing, web shear connectors, or projection of the bars.