Date of Graduation

8-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Hale, W. Micah

Committee Member

Heymsfield, Ernest

Second Committee Member

Pleimann, Larry G.

Third Committee Member

Springer, William T.

Keywords

Applied sciences; Developmental length; Lightweight concrete; Prestressed concrete; Self-consolidating concrete; Strand bond; Transfer length

Abstract

Lightweight self-consolidating concrete (LWSCC) is a relatively recent advancement in concrete technology. The reduced dead load from lightweight concrete is beneficial for precast elements and for elements where dead load is a significant portion of the total load, such as prestressed bridge girders. Self-consolidating concrete (SCC) is a specially proportioned concrete mixture that consolidates under its own weight without the need for vibration. The combination of lightweight concrete and self-consolidating behavior provides the benefits of both. Bond of prestressing steel has been a much debated topic since the 1950s. Limited data are available on the transfer and development length of strands cast in SCC and even less for strands cast in LWSCC. The differences in material properties resulting from the lightweight coarse aggregate and mix proportioning used for LWSCC have potential to lead to longer transfer and development lengths than those for conventional concrete, which can be detrimental to shear and flexural performance. The transfer and development length equations provided in the ACI Building Code Requirements for Structural Concrete and AASHTO Bridge Design specifications are based on studies performed using conventional concrete. This research project examined the transfer and development length of LWSCC specimens using 0.6 in. (15.2 mm) Grade 270 prestressing strand. Four specimens were cast from each mixture consisting of a combination of expanded clay, expanded shale, or limestone aggregate and a compressive strength of 4000 psi or 6000 psi (28 MPa or 41 MPa) at prestress release. Results were compared between the mixtures, to the code equations, and to previous research. The bond performance of LWSCC with a release strength of 6000 psi (41 MPa) was very similar to normal weight SCC, the transfer lengths for both strength levels were accurately predicted by the code equations, and the measured development lengths were significantly less than those predicted.

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