Bond Behavior of Prestressed Reinforcement in Beams Constructed with Self-Consolidating Concrete

Abstract

Accurate behavioral characteristics of self-consolidating concrete (SCC) should be established prior to its widespread implementation in prestressed members. This thesis describes an investigation of bond behavior of prestressed reinforcement in SCC flexural members. Sixteen eccentrically prestressed T-beams were subjected to transfer and development length testing. One conventional mixture and three SCC mixtures were used to construct the beams. The conventional mixture was a moderate-strength mixture with a compressive strength at prestress transfer of 5,000 psi. The three SCC mixtures included two moderate-strength mixtures with compressive strengths at prestress transfer of approximately 5,500 psi and one high-strength mixture with compressive strength at transfer of 9,900 psi.

SCC transfer bond behavior only differed significantly from that of the standard mixture at flame-cut ends of the moderate-strength SCC mixture with a 50% replacement of GGBF slag. On average, specimens constructed with higher compressive strengths at transfer had shorter transfer lengths than specimens that were constructed with lower concrete strengths at transfer. The average decrease in transfer length with increasing concrete strength could be accurately estimated by assuming the transfer length is inversely proportional to the square root of the concrete strength at transfer. Current design provisions for transfer length that do not include concrete strength as a parameter, including equations suggested by ACI 318 and AASHTO, do not adequately predict transfer length for specimens cast with SCC or conventional concrete.

The development length test program was characterized by flexural tests of all specimens. Results indicated that SCC mixture proportioning did not have an adverse effect on the overall flexural bond performance—either with respect to current design procedures or with respect to the comparable conventionally consolidated mixture. The flexural bond length predicted by the ACI 318 and AASHTO expressions proved to be conservative for all SCC specimens.