Self-consolidating concrete (SCC) is being implemented throughout the US. Some advantages of SCC include its ease of placement, reduced labor requirements for placing the material, reduced noise when placing, and its improved finish quality. Clearly there are benefits of using this material. However, the AASHTO LRFD specifications were developed based on material characteristics of conventional, normal strength concretes. Because of this, engineers and designers are reluctant to specify and use SCC for bridge applications, possibly making the potential benefits of this material underutilized. This research investigated compressive strength development, modulus of elasticity (MOE), modulus of rupture (MOR), and splitting tensile strength (STS) of SCC mixtures specifically designed for precast, prestressed, concrete bridge girders. The experimental program included two target 16-hour compressive strength levels and two coarse aggregate types (river gravel and crushed limestone) with varying volume fractions. The measured mechanical properties for the SCC mixtures were compared with the results of conventional concrete (CC) mixtures of similar release strengths, as well as the estimated values from the 2006 AASHTO LRFD prediction equations. Results indicate that the AASHTO equations either predict the mechanical properties of SCC fairly well or underestimate the properties of SCC.

This paper summarizes a testing program undertaken to evaluate the uniformity of bond strength between concrete and reinforcing bars positioned at various depths of experimental wall elements. In total, four self-consolidating concrete (SCC) mixtures and three conventional flowable mixtures were prepared with different combinations of viscosity-modifying admixtures and high-range water reducers. The concrete mixtures were used to cast experimental wall elements measuring 1.54 m in height, 1.1 m in length, and 0.2 m in width. Two of the walls were steam-cured, while the remaining four elements were air-cured. Each wall had 16 reinforcing bars, four per row positioned at four levels, that were subjected to pullout tests at 1 and 28 days of age. The concrete mixtures were prepared with Type III cement, 20% Class F fly ash substitution, and a low w/cm of 0.37, which is typical of structural precast concrete construction. The targeted 1-day compressive strength was 40 MPa. Uniform distribution of in-situ compressive strength and adequate bond to the reinforcing bars were obtained with relatively small variations along the experimental wall elements. The 1- and 28-day top-bar effect ratios varied between 1 and 1.4 for the majority of the test results. These values were lower for the air-cured mixtures compared to the steam-cured mixtures. The top-bar effect is shown to be sensitive to the type of VMA used in the SCC.

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.

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.

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.