This paper describes the repair of a high-strength silica FUME concrete structure using a high-strength repair material which also contains silica FUME The repair represented the largest single application of this material and the largest single use of low-pressure spraying of the repair material. Information is provided on the repair procedures, proficiency of the nozzlemen, acceptance criteria applied to this type of operation. Because of the lack of actual in-situ bond and compressive strength data on high strength concrete in the literature, all of the actual in-situ test results are provided for this repair. Approximately 1,300 m3 of the repair material was used to repair 24,000 sq. meters of concrete surface damaged during a slipform operation. The damaged concrete had compressive strengths in the range of 78 to 82 MPa. The repair material had a target compressive strength of 80 MPa and an in-situ bond strength requirement (minimum) of 1.5 MPa. Using low-pressure spraying techniques because of confined working areas, the repairs were successfully completed over a 24 week period. Compressive strengths of cores from sprayed production test panels averaged 85 MPa at 28-DAYS. The in-situ bond strength of the repairs did not appear to increase with age and averaged 1.87 MPa for all ages evaluated.

The development of a high performance, high volume fly ash (HVFA) concrete incorporating a small amount of silica fume, and part replacement of both cement and sand with fly ash (FA) is reported. This paper presents the results on the engineering properties such as strength, dynamic modulus and swelling/shrinkage of such high volume fly ash concrete. The mixtures were proportioned to give 30 to 40 MPa cube strength at 28 days. Two basic mixtures with total binder contents of 350 kg/m3 and 450 kg/m3, and, with a minimum portland cement content of 150 and 200 kg/m3 respectively, were investigated. In each mixture, about 60 per cent of the cement was replaced by fly ash. In addition, in some mixtures, a nominal amount of silica fume was incorporated, and in some others, additional FA was incorporated as replacement for sand. The results show that the total binder content had little effect on strength, swelling strain and drying shrinkage, but had a significant effect on the dynamic modulus of elasticity implying a clear densification of the microstructure by fly ash and silica fume. On the whole, HVFA concrete with a nominal amount of SF, and FA as part replacement of both cement and sand showed better overall performance. The engineering properties of the HVFA concretes investigated show good potential for use in structural and mass concrete applications.

The evolution of the microstructure of a hydrated fly ash-belite cement (HFABC) has been studied during a period of 90 days after mixing. The cement was synthesized from a mixture of fly ash (ASTM Class F), lime and water by a hydrothermal procedure. The microstructure characterization at different times was followed by mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and EDS, X-ray diffraction (XRD), thermogravimetry (TG) and analytical techniques. Besides, the compressive strength was determined and correlated to the microstructure characteristics. The pore solution was expressed and analyzed at different periods of the hydration reaction.

This report presents the properties of hardened super workable concrete in which ground granulated blast furnace slag was used, and compare these properties with the corresponding properties of ordinary concrete. Two ground granulated blast furnace slags of fineness 4500 cm2/g and 6150 cm2/g were used for this research. The replacement ratio of cement by blast furnace slag were controlled to O%, 30%, 5O%, and 70%. The concrete specimens were cured by four different methods; in air continuously, in water for 3 days and then in air, in water for 7 days and then in air and in water continuously. The super workable concretes, which were cured in water suffciently at early ages, exhibited higher performance in compressive strength, water permeability, resistance to freezing and thawing and carbonation in comparison with ordinary concrete. As for the porosity as well, the total pore volume of these concrete were lower than that of ordinary concrete. This excellent performance was more remarkable in the super workable concrete with BFS of fineness of 6000 cm2/g. But, these properties of: super workable concrete with BFS were more sensitive to initial water curing period than the concrete without BFS.

The effects of steam curing conditions such as the presteaming period and the maximum curing temperature on the compressive strength of fly ash concrete were investigated and compared with those of plain concrete in order to use fly ash for precast concrete products. The replacement ratios of cement by fly ash were 0, 20 and 40 percent. The presteaming period ( 2, 4 and 6 hours ) and maximum temperature during steam curing ( 65°C and 80°C ) were varied in this test. The compressive strength of 100 X 200 mm cylinder specimens were determined at the ages of 1, 7 and 28 days. As a result of this investigation, the adoption of a longer presteaming period of 4 to 6 hours and a maximum curing temperature from 65°C to 80°C is recommended for the steam curing of fly ash concrete to obtain higher strength at various ages.