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.

An experimental program was developed to investigate the time-dependent behavior of prestressed concrete beams constructed with high-strength self-consolidating concrete (SCC). The study involved eight concrete T-beams, each prestressed with a single deformed wire. Four of the beams were cast with high-strength self-consolidating concrete, while the other four were cast with conventional high-strength concrete. Half of the beams were loaded with a sustained load 29 days after release while the other half of the beams were kept unloaded. Testing consisted of monitoring concrete and reinforcement strains, prestress losses, and beam camber for a period of 300 days after release. Elastic modulus, creep, and shrinkage tests were simultaneously conducted on companion cylinder specimens to better define the material properties of the two mixes used in the study. Results showed that the time-dependent behavior of the high-strength SCC beams was inherently similar to that of the conventional high-strength concrete beams. However, the measured time-dependent prestress losses and camber were significantly greater for the self-consolidating high-strength concrete. Complex prediction methods that are flexible enough to consider the actual material properties of the SCC or HSC were found to do the best job of predicting results.

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.

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.

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.