| Recent research in bond suggested that concrete strength can affect the bond strength between prestressing strand and concrete. However, earlier research from the 1960's through the 1980's suggested that concrete strength does not affect the bond between prestressing strand and concrete. Neither the ACI Building code nor AASHTO Bridge code makes provision for concrete strength, though its been suggested that concrete strength parameter is needed in the equations. Codes based on early research therefore do not account for variations in concrete strength. The purpose of the research is to investigate what effects, if any; concrete strength has on the bond of prestressing strand to concrete. To investigate these effects, NASP Bond tests on strands are performed at various concrete strengths. The tests demonstrated that bond improve with increasing concrete strengths. The thesis also reports on the development of HPC for use in precast/prestressed concrete products. This thesis project includes the development of concrete mix proportions for four types of concrete with varying compressive strengths from 4,000 to 15,000 psi. Beams were made in a precast concrete plant with strength ranging from 6,000 psi to about 15,000 psi. |
