International Concrete Abstracts Portal

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.

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.

The precast industry has always been looking for ways to improve production. Be that ease of casting or finishing, faster turnaround or better economics due to less damage or reduced concrete costs. The advent of self consolidating concrete (SCC) has enabled some of these aspects to be realised. The development of SCC and new mixture design procedures has improved certain facets of the precast industry. However, the excessive use of fillers or very high cement contents has had equal drawbacks for the use of SCC in this environment. With the advances in software allowing very precise particle packing analyses to be made of the materials, new mix designs with lower total binder contents - and little or no fillers - are possible. Designs with supplementary cementitious materials (SCMs), including silica fume, can be very effective for SCC, not only giving excellent flow and non-segregation, but also enhancing the finished quality of the concrete. This paper reviews the use of silica fume in SCC, information from the Technically Optimised Piling Concrete (TOPIC) research in the UK, and gives examples of the use in some precast operations in Sweden.