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.
ADMIXTURE FOR CONTROLLING BLEED IN CEMENT GROUT USED IN POST-TENSIONING
The bleed characteristics of neat cement grout are well known. With usual mixing procedures and grout admixtures it can be expected that water separation will occur due to sedimentation of the suspension of cement and admixture in water. This is particularly exaggerated with strand-type tendons. To control this characteristic and the general pumping problems grout blockages with dewatering, a grout admixture has been developed which can control the bleed as desired. The basic research in developing this admixture used short strand tendons to determine the different water retentive characteristic of admixtures. However, based on these tests, it was found that the vertical scale factor of pressure is important. Thus, a pressure filter test was also sued to determine the water retentive characteristic of various grouts. Based on this research, a grout admixture was developed with the property of high water retentivity such that for instance no water loss will occur in the grout when the pressure is maintained at 100 atmospheres over 10 min. For shorter durations, water retentivity is fully maintained for even higher pressures. /Author/