Structural Performance of Self-Consolidating Concrete in AASHTO Type I Prestressed Girders

Abstract

As part of a larger investigation sponsored by the Alabama Department of Transportation (ALDOT) into the use of self-consolidating concrete (SCC) in bridge girders, this thesis documents a structural investigation of SCC in AASHTO Type I precast, prestressed girders. Six test girders were subjected to transfer length and flexural testing. Three separate concrete mixtures, two girders per mixture, were used to construct these specimens. One mixture was a moderate-strength, conventional-slump concrete mixture, similar to the concrete used in typical ALDOT girders, with a compressive strength at prestress transfer of approximately 5,000 psi. The other two mixtures consisted of moderate-strength SCC and high-strength SCC, with compressive strengths at prestress transfer of approximately 5,000 psi and 10,000 psi, respectively. No significant difference in transfer bond behavior was found between the full-scale SCC girders and the conventional concrete girders. High-strength SCC girders had shorter transfer lengths than moderate-strength (SCC and conventional) girders. This behavior was accurately estimated by assuming the transfer length was directly proportional to the prestress magnitude and inversely proportional to the square root of the concrete compressive strength at transfer. After normalization for these effects, there was no discernible difference in the magnitude of the transfer lengths between the concrete types. Based on comparisons to smaller specimens in earlier phases of the study, transfer lengths decreased with increasing cross-section size for all concrete types. Significant growth of transfer length over time was found, demonstrating that reliable estimates of long-term transfer lengths are difficult to estimate solely on measurements of initial transfer lengths. In conjunction with the transfer length testing, a strand draw-in program was employed in order to assess its ability to accurately predict transfer lengths. After a composite, cast-in-place concrete deck was added to each girder, flexural testing was performed near each girder end, resulting in two flexural tests per girder. Embedment lengths were varied for each test in order to bracket the AASHTO strand development length. Results indicated that the SCC mixture proportioning had no adverse effects on the overall flexural performance, and the flexural bond lengths were conservatively predicted by the relevant ACI and AASHTO expressions. Similarly, the SCC girders exhibited comparable service-level performance to the conventional girders. Based on observations of deck separation and slip, deck-to-girder interface shear transfer was less effective for the SCC girders than for the conventional girders. This was attributed to inadequate surface roughening of the SCC girders.