International Concrete Abstracts Portal

SP-247CD This CD-ROM is a collection of papers prepared for a session held at the ACI 2007 Fall convention in Puerto Rico on the hardened properties and performance of SCC developed for use in precast prestressed applications. The papers relate to SCC in prestressed applications and are organized as follows: 1) mixture proportioning; 2) mechanical properties; 3) time-dependent deformations; 4) flexural and shear behavior; 5) bond behavior; 6) prestress losses; and 7) the structural behavior of full-scale precast prestressed elements made with SCC.

As a part of an ongoing study at the University of Minnesota, self-consolidating concrete (SCC) has been developed successfully with locally available materials from two precast concrete plants for use in precast prestressed bridge girders in the State of Minnesota. Four SCC mixes (i.e., two mixes per plant) were designed, evaluated, and used to cast four SCC precast prestressed bridge girders. Variations in the SCC mixes included cementitious materials (ASTM Type I and Type III cement, and Class C fly ash), natural gravel and crushed stone as coarse aggregate, and several admixtures. In addition to SCC girders, a conventional concrete girder was cast simultaneously on the same precasting bed for each plant. The girders were instrumented to monitor both short-term and long-term performance, which included transfer length, camber, and prestress losses. In addition, companion cylinders were cast to monitor compressive strength and modulus of elasticity over time. The test results indicate that the overall performance of the SCC girders was comparable to that of conventional concrete girders and could be predicted using existing design equations.

The mix design deviations required to achieve self-consolidating concrete (SCC) have raised concerns on the effect that this may have on the bond performance of reinforcement. The paper summarizes an investigation on the effect of SCC mix proportioning on the bond behavior and bond-related parameters of transfer and development length of 13mm (0.5 in.) diameter prestressing strands. Three SCC mix designs that bound the common approaches to achieve SCC and a reference normally consolidated concrete (NCC) mix were used. Direct bond strength was assessed by simple strand pull-out tests. Using laboratory-scale T-beams, transfer length was evaluated by concrete surface strains and draw-in measurements, while development lengths were estimated through flexural tests. Results indicated the bond performance of strand in SCC to be lower than for NCC. Transfer and development lengths for SCC were longer than for NCC; yet, on average, these lengths still met the ACI code recommendations. Bond performance for the different SCC mixes was distinct, consistent and bounded by the extreme cases considered. Given the variability and uncertainties in the experimental methods and code equations, results from this study indicate that bond performance on SCC, as it pertains to anchorage lengths, is adequate.

The use of Self-Consolidating Concrete (SCC) is becoming more prevalent in both building and bridge applications. Newcrete Products in Roaring Spring, Pennsylvania has experience with use of an SCC mix in parking structure members such as double-tee sections. While SCC is not yet widely used in bridge members in Pennsylvania, this application is also of interest. Newcrete in cooperation with Penn State University developed a program for bond evaluation of the Newcrete SCC mix. The objectives of the program are as follows: 1) to compare the Newcrete SCC mix with the current design code requirement for transfer length, 2) to determine the pull-out capacity of the strand in the SCC mix with the Moustafa test, 3) evaluate the failure mode at ultimate, and 4) compare the results of the SCC mix with a standard (non-SCC) Newcrete mix.

While the characteristics of self-consolidating concrete (SCC) do not affect the bending capacity, there is an influence on the bond strength and shear capacity. The effect on the bond behavior of strands in SCC is a subject of some controversy in current literature. Therefore, pull-out tests and full-scale tests on the transfer length have been performed to describe the bond capacity of SCC with gradual release of prestress. It is shown that the bond behavior depends on the concrete mixture. The bond capacity of SCC containing limestone powder is comparable to conventional vibrated concrete while the bond capacity of SCC with fly ash is reduced by approximately 20%. The shear capacity of prestressed beams has been determined by tests with different shear reinforcement ratios. The tests revealed that SCC does not significantly influence the shear capacity although the smaller aggregates and the higher content of cement paste reduce the crack-friction capacity.