International Concrete Abstracts Portal

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.

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.

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.

To achieve adequate flow and stability characteristics, self-consolidating concrete (SCC) typically has higher paste and lower coarse aggregate volumes than conventional concrete (CC). Because the coarse aggregate content directly affects aggregate interlock, SCC may not provide the same shear capacity as CC. This research investigated the influence of SCC aggregate and paste volumes on shear capacity and compared these results with those obtained from similar CC samples. Twelve SCC mixture proportions were evaluated with three main variables: two 16-hour release strengths (5 and 7 ksi), two aggregate types (river gravel and limestone), and three different volumes of coarse aggregate. Four CC mixture proportions were used as control mixtures and consisted of two release strengths (5 and 7 ksi) and two coarse aggregate types (river gravel and limestone). A total of 48 push-off samples (36 SCC and 12 CC samples) were fabricated and assessed for shear characteristics. The crack slip, crack width, normal stress, and shear stress were measured to evaluate the aggregate interlock of the SCC and CC. The relationships between these parameters are presented to illustrate the aggregate interlock behavior for samples containing SCC and CC. Energy absorption methods were used to quantitatively assess the aggregate interlock. These results indicate that the SCC samples tested in this research program exhibit less aggregate interlock than the CC samples.

A demonstration bridge project in Michigan is allowing the state’s Department of Transportation to evaluate the short- and long-term structural performance of self-consolidating-concrete (SCC) in bridge beams. The M-50/US-127 Bridge over the Grand River (Jackson, Michigan) features SCC prestressed box beams in 3 of its 6 beams. Three SCC mixture proportions are being evaluated against a reference normally consolidated concrete mixture (NCC). Before implementation, performance of the SCC beams was evaluated through full-scale flexure and shear testing to ensure similar performance to the NCC beams. The SCC beams met the nominal design capacities and their performance was essentially the same as the NCC beams. With this validation, the demonstration bridge with its SCC beams was completed in October 2005. A strain and temperature continuous monitoring system was placed on the SCC beams and one NCC beam to evaluate long-term performance. Collected data since December 2005 indicates that the field performance of the SCC beams is similar to the NCC beams.