HIGH PERFORMANCE ADMIXTURES FOR SELF-COMPACTING CONCRETE : MECHANISM AND APPLICATION IN CHINA BUILDING
In this paper, the basic functional mechanism of high performance admixture (HPA) in SCC is discussed combining with the development of modern concrete admixture. Major applications of JM-SCC in China construction including hydraulic hydropower, transportation and industrial building, such as the Three Gorges Dam, the Gongboxia Hydropower Station, the Nanjing-Hangzhou Express Way, etc. are presented.
Self-compacting concrete. Development, present use and future
Self-compacting concrete was first developed in 1988 in order to achieve durable concrete structures. Since then, various investigations have been carried out and the concrete has been used in practical structures in Japan, mainly by large construction companies. Investigations for establishing a rational mix-design method and self-compactability testing methods have been carried out from the viewpoint of making it a standard concrete. Recommendations and manuals for self-compacting concrete were also established.
BOND STRENGTH OF REINFORCING BARS IN REINFORCED SHOTCRETE
There is not yet a consensus on the quality parameters for the steel-concrete bond for shotcrete reinforced elements or whether or not shotcrete is comparable in performance to regular cast-in-place concrete. This paper presents the results of a series of lab experiments on the bond strength of lap-spliced beams cast using the wet shotcrete process: the American Concrete Institute bond strength equations were used to evaluate the performance of shotcrete beams. The beams were compared to cast-in-place concrete beams of the same dimensions, steel configurations, and approximately the same concrete compressive strength. The bond strength of beams repaired using the wet process was also examined. The study includes the analysis of the performance of a new type of shotcrete admixture which enhances the steel-concrete bond. The results reveal that the bond strength is slightly lower for bottoms cast shotcrete, but that the top bar bond strength is increased considerably for the shotcrete beams, when compared to regular cast-in-place concrete, due to the reduced segregation and bleeding generated during the shotcrete process. When water soluble polymers are added to shotcrete, the performance of shotcrete as compared to control shotcrete is superior due to improved rheological behavior of concretes containing pumping aid and sag resistance additives (PASRA).