Prestress Losses in Beams Cast with Self-Consolidating Concrete


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Title: Prestress Losses in Beams Cast with Self-Consolidating Concrete

Author(s): E.D. Ruiz, B.W. Staton, N.H. Do, and W. Micah Hale

Publication: Special Publication

Volume: 247


Appears on pages(s): 93-104

Keywords: beams; prestress losses; self-consolidating concrete

Date: 9/1/2007

Self Consolidating Concrete (SCC) is a recent advancement in the concrete industry. SCC is a type of concrete that can be placed without consolidation and has become widely accepted in the precast industry in the United States. The interest of SCC in bridge girders is also growing. This research program compares the prestress losses of SCC beams to those of conventional concrete with similar compressive strengths. The research program also compares the predicted losses to measured losses. A total of 20 prestressed beams were cast, and of those 20 beams, prestress losses were measured on 10 beams. Each beam was 6.5 inches (165 mm.) wide and contained two 0.60 inch (15.2 mm.) diameter prestressing strands. The beams measured 18 feet (5.5 m.) in length with a height of 12 inches (254 mm.). Two SCC mixtures were used to cast 7 beams and a conventional concrete mixture was used in the remaining 3 beams. The SCC and conventional beams had concrete compressive strengths that ranged from approximately 7 to 10 ksi (48 to 69 MPa) at release and 10 to 13 ksi (69 to 90 MPa) at 28 days. Prestress losses were measured through the use of vibrating wire strain gages. Early test results indicate that at similar compressive strengths, there was little difference between the losses of the SCC beams versus those of the conventional concrete beams. For all beams, the measured losses (excluding relaxation) ranged from 19.2 ksi to 25.6 ksi (132 to 177 MPa) at an average age of 124 days.