International Concrete Abstracts Portal

Case histories are presented to illustrate applications of nondestructive evaluation (NDE) methods that use stress waves to characterize the conditions of concrete construction. The case histories discuss the following NDE methods and applications: (1) impact echo to evaluate cracking in a 1923 thin-arch concrete dam on the downstream face; (2) ultrasonic pulse velocity to define the severity of cracking damage in precast bridge segments and for quality assurance of epoxy injection repairs; and (3) ultrasonic crosshole sonic logging with PC-based instrumentation for quality assurance of the integrity of concrete placement in drilled shaft and slurry wall foundations. Comparisons of NDE results defined the extent and nature of sound and defective concrete conditions.

Abrasion resulting from the movement of sea ice and fresh water ice must be considered during the design of concrete marine structures and concrete bridge piers for regions where the sea freezes in winter. Such areas include the Arctic Ocean, the Sea of Okhotsk, the Gulf of Bohai, the Beaufort Sea, the Bering Sea, the Gulf of Bothnia, and places where rivers freeze in winter. Movement of the ice sheet is both horizontal, caused by the tidal currents and wind, and vertical, due to tidal ebb and flow. Therefore, it is very important in the design of concrete structures in very cold regions to clarify the amount of abrasion due to ice-concrete motion. Through a systematic series of experiments, the authors have obtained the following information: 1) a relationship between sliding distance and amount of abrasion for various concretes and coatings; 2) a relationship between ice pressure on a concrete specimen (contact pressure) and amount of abrasion at the concrete surface; 3) the relationship between ice strength and abrasion rate; 4) the relationship between abrasion rate for various concretes and ice with fine entrained sand; 5) the degree of contamination by sand in actual river and lake ice in Hokkaido, Japan; and 6) a method for estimating the abrasion of concrete structures due to a movement of an ice sheet.

Presents a scheme to rescue a reinforced concrete building from the severe attack of sulfate water. Our practical solution to this problem included: replacement of spread footings, making the basement an inside-out water tank, protection of columns against sulfate attack, and stabilization of soil in the vicinity of the rectangular spread footings.

This paper describes the structural engineering aspects of the refurbishment of the grandstands at the Royal Hong Kong Jockey Clubs, Happy Valley Racecourse. Racing at Happy Valley takes place during the months of October to May and therefore demolition and refurbishment works could only be carried out during the off-racing season. To meet a very tight program a total of four working phases were planned from June 1987 to September 1989 as follows. Phase 1 included the construction of a new infield stand enclosed within a steel-framed structure supporting a profiled steel roof to provide betting and catering facilities for 6000 racegoers and refurbishment works to existing stands M2 and M3 at ground and first floor levels. This phase was designed and constructed within a 22-week period. Phases 2,3, and 4 involved extensive refurbishment and addition of structures to existing buildings. A particular requirement was to produce an elegant and uniform roof to cover existing and proposed mechanical plants. The structural systems adopted respected the constraints of these existing buildings and provided an integrated framework for extensive building services elements. Phases 2A and 2B involved the complete gutting to bare reinforced concrete frame, addition of new plantroom floors and hanging rear stairs, and strengthening of foundations and structures to the P1 and P2 stands. Phase 3 involved the creation of additional roof-top space for plantrooms, press, and broadcasting facilities. New steel frames were placed at existing roof levels and the existing frame was strengthened. The work for Phase 4 included the provision of a two-story lightweight steel frame for plantrooms, daylet boxes, and service ducts hung at the rear of the building for services distribution.

Efficiency of repairs conducted for a jetty damaged by chloride salt attack in Toyko Bay was investigated by field and laboratory tests after five years of repair. Investigation results on durability of surface coatings, chloride ion concentration in concrete, and corrosion of reinforcing bars are presented. Visual inspection, and elasticity or crack bridging ability and adhesion strength to concrete indicated that the durability of surface coatings is sufficient. There is no significant difference in distribution of chloride ion concentration in coated concrete before and after repairing. Dispersion of chloride ion in surface coated concrete was numerically analyzed and the results show that the surface coatings decrease the existing chloride content in surface area as the chloride ions disperse into deeper area by degrees. Reinforcing steels in the coated concrete were found predominantly to be in sound condition, except some did show corrosion where the chloride ion content exceeds a critical value. This investigation also demonstrates the importance of maintenance after repair.