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Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements (2009)

Chapter: Chapter 2 - Background and Research Approach

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Suggested Citation:"Chapter 2 - Background and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2009. Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements. Washington, DC: The National Academies Press. doi: 10.17226/14188.
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Suggested Citation:"Chapter 2 - Background and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2009. Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements. Washington, DC: The National Academies Press. doi: 10.17226/14188.
×
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Suggested Citation:"Chapter 2 - Background and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2009. Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements. Washington, DC: The National Academies Press. doi: 10.17226/14188.
×
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Suggested Citation:"Chapter 2 - Background and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2009. Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements. Washington, DC: The National Academies Press. doi: 10.17226/14188.
×
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Suggested Citation:"Chapter 2 - Background and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2009. Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements. Washington, DC: The National Academies Press. doi: 10.17226/14188.
×
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Suggested Citation:"Chapter 2 - Background and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2009. Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements. Washington, DC: The National Academies Press. doi: 10.17226/14188.
×
Page 17
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Suggested Citation:"Chapter 2 - Background and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2009. Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements. Washington, DC: The National Academies Press. doi: 10.17226/14188.
×
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Suggested Citation:"Chapter 2 - Background and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2009. Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements. Washington, DC: The National Academies Press. doi: 10.17226/14188.
×
Page 19
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Suggested Citation:"Chapter 2 - Background and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2009. Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements. Washington, DC: The National Academies Press. doi: 10.17226/14188.
×
Page 20
Page 21
Suggested Citation:"Chapter 2 - Background and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2009. Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements. Washington, DC: The National Academies Press. doi: 10.17226/14188.
×
Page 21

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12 2.1 Background Use of SCC in the construction of precast bridge members and bridge substructures and in the repair of bridges has been limited in the United States. Properly designed SCC is expected to provide similar properties as the conventional counterparts except for the high workability. However, changes in mix design and fluidity of SCC can result in SCC with hardened properties and performance that are different from that commonly expected from conventional concrete. Proper selection of material constituents and proper proportion- ing are necessary for achieving the desired workability and performance of SCC. The factors that significantly influence the design, constructability, and performance of precast, prestressed bridge elements with SCC need to be identified. There is also a need to develop guidelines for the use of SCC in bridge elements and to recommend changes to AASHTO LRFD Specifications. These guidelines will provide highway agencies with the information necessary for considering con- crete mixtures that are expected to expedite construction and yield economic and other benefits (e.g., better surface finish, lower labor cost, etc.). For successful design of SCC, some factors require greater attention than is generally required for conventional concrete, including type and size and grading of coarse aggregate, com- position and content of binder materials, and w/cm. Proper selection of material constituents is also necessary for worka- bility and performance of the hardened concrete. A number of test methods have been used to characterize workability of SCC, including filling ability, passing ability, and segregation resistance. However, no single test method has been found to fully characterize all relevant workability aspects of SCC. Selection of proper combined test methods can facilitate workability testing protocol and provide means for quality control of field applications. Knowledge of the compressive strength, elastic modulus, and flexural strength of concrete is required for estimating camber of prestressed members at the release of the pre- stressing load, and for determining elastic deflections caused by dead and live loads, axial shortening and elongation, and prestress losses. Literature review showed that the modulus of elasticity of SCC could be as low as 80% of that for HPC of normal consistency because of the lower coarse aggregate vol- ume of SCC [Holschemacher and Klug, 2002]. However, under air-drying conditions, the elastic modulus of SCC can be higher than that of normal concrete at long term. Limited published data are available on relationships between flexural strength and compressive strength of SCC, and applicability of the various code models to SCC need to be validated. Typically, SCC mixtures are proportioned with higher binder content, lower coarse aggregate volume, and smaller MSA, which increase thermal, autogenous, and drying shrink- age, and creep leading to high loss of prestress and excessive deflections and elastic shortening. Therefore, creep and dry- ing shrinkage characteristics of SCC need to be determined and considered in the design of precast, prestressed bridge elements. According to the literature survey, there seems to be some discrepancy regarding the visco-elastic properties of SCC because of differences in mix design (w/cm), type and content of coarse aggregates, type of chemical admixture, and testing exposure. It is reported that the creep potential of SCC appears to be slightly higher than that of conventional concrete made with the same raw materials and having the same 28-day compressive strength [Attiogbe et al., 2002; Pons et al., 2003; Byun et al., 1998]. Depending on the selected binder, w/cm, and ambient temperature at the precasting plant, the use of new generation HRWRA may eliminate the need to use radiant heat or steam curing. SCC used in precast, prestressed applications is typically proportioned with a low w/cm (0.32 to 0.36) to enhance stabil- ity of the plastic concrete. Relatively low w/cm values, coupled with high content of binder, lead to a greater degree of auto- genous shrinkage than in conventional concrete. Such type of shrinkage also increases with increased fineness of the binder and fillers in use. Therefore, drying shrinkage, autogeneous C H A P T E R 2 Background and Research Approach

13 shrinkage, and thermal contraction have to be considered in the mix design process and in the structural detailing of the prestressed element. Studies have shown that the scatter between measured and predicted drying shrinkage values is greater in the case of SCC than that for normal concrete. Experimental shrinkage strains for SCC were found to be larger than those estimated by var- ious prediction models [Byun et al., 1998]. Also, comparison of experimental creep data to those obtained from major creep-prediction models indicated differences. Work is re- quired to compare creep and shrinkage data of SCC mixtures made with representative mix designs and the material con- stituents available in the United States with those obtained from prediction models. The stability of SCC is a key property in ensuring uniform mechanical properties and adequate performance of precast, prestressed concrete bridge girders. Properly designed SCC mixtures can exhibit uniform distribution of in-situ compres- sive strength. Bond strength and its uniformity along the height of the girders can be influenced by flow properties of the SCC, grading of the aggregate, and content of fines. Some studies have found that bond strength of reinforcement to SCC can be lower than that to normal concrete [Koning et al., 2001; Hegger et al., 2003]. Other studies, however, have shown that for a given compressive strength, reinforced concrete members made with SCC can develop higher bond strength than in the case of normal concrete [Dehn et al., 2000; Chan et al., 2003]. Bond strength that can be developed between SCC and pre- stressed strands and its uniformity along the height of cast wall elements were investigated in this project. The structural design concerns related to the use of SCC for constructing prestressed girders include the likely lower modulus and greater shrinkage of SCC and the possible larger prestress losses and the reduced shear resistances resulting from the use of a smaller maximum aggregate size or a smaller volume of coarse aggregate. 2.2 Research Approach Literature Review As a part of the project, an extensive literature review of factors affecting performance of SCC in structural applications was carried out (details of the literature review are summarized in Attachment D). The literature review pertained to precast, prestressed SCC, including: • Test methods and acceptance criteria of fresh characteristics of SCC, • Requirements for constituent materials and mix design considerations, • Production and placement issues, • Factors affecting mechanical properties and structural performance, • Factors affecting visco-elastic properties, and • Durability characteristics. Experimental Work Plan The experimental program was conducted in three phases. Phase I addressed test methods and acceptance criteria; Phase II addressed mixture proportioning and material character- istics; and Phase III addressed structural performance of full- scale girders. Details of this work are discussed below. Phase 1: Test Methods and Acceptance Criteria for SCC This work included: • A parametric study of various concrete mixture parameters and constituent materials to help develop recommendations for mix design of SCC for precast, prestressed applications; • Evaluations of the effect of MSA, aggregate and binder types, and w/cm on workability and compressive strength development of SCC mixtures suitable for precast structural applications; • Comparison of workability test methods that can be used for mix design and quality control of SCC, and suggestion of performance specifications; and • Correlation of key workability responses to basic rheological parameters (in particular, plastic viscosity). The parametric study of 24 non–air-entrained SCC mixtures (No. 1 through 24 in Table 4) was conducted to evaluate the influence of binder type, w/cm, and coarse aggregate type and nominal size on workability and compressive strength devel- opment of SCC mixtures designated for the construction of precast, prestressed AASHTO girders. These mixtures were prepared using either crushed aggregate or gravel of three dif- ferent MSA [3⁄4, 1⁄2, and 3⁄8 in. (12, 19.5, and 9.5 mm)], w/cm of 0.33 and 0.38, and three binder compositions (Type III cement with 30% slag replacement, Type I/II cement, and Type III cement with 20% Class F fly ash). Three air-entrained SCC mixtures (No. 25 through 27 in Table 4) were prepared with low w/cm to obtain an initial air volume of 4% to 7%. Three SCC mixtures (No. 28 through 30) similar to mix- tures No. 1 through 3, having relatively low filling ability (deformability) with slump flow values of 23.5 to 25.0 in. (600 to 640 mm), and three other mixtures (No. 31 through 33) similar to mixtures No. 4 through 6, presenting relatively high slump flow of 28.0 to 30.0 in. (710 to 760 mm), were prepared to evaluate the effect of fluidity level on filling abil- ity, passing ability, filling capacity, stability, and compressive strength development.

In addition, 10 SCC mixtures (No. 34 through 43) with proportions similar to those of mixture No. 16 were used to evaluate the repeatability of workability tests. Each concrete mixture was tested for several workability characteristics, com- pressive strength, and modulus of elasticity as indicated in Table 5. The test methods that were used to evaluate the work- ability of SCC are described in Attachment D. Several 4 × 8 in. (100 × 200 mm) concrete cylinders were cast within 10 minutes to evaluate the compressive strength and modulus of elasticity at 18 hours of age. The cylinders were cast in one lift without any mechanical consolidation. The specimens were demolded at 16 hours of age and tested at 18 hours. Some of the specimens were cured in the labora- tory at 73 ± 4°F (23 ± 2°C) under wet burlap, while others were steam cured to determine early-age strength and mod- ulus of elasticity. For the determination of strength develop- ment beyond 18 hours, the samples were air cured in the molds under wet burlap at 73 ± 4°F (23 ± 2°C) for 1 day be- fore demolding and storing in a moist-curing chamber. Mixture Proportioning Guidelines. Based on the results of the parametric study, and consideration of the effects of w/cm, binder type, and nominal size and type of coarse aggre- gate on workability characteristics and development of com- pressive strength, guidelines for the proportioning of SCC for use in precast, prestressed applications were proposed. Comparison of Responses of Various Test Methods. Correlations among the various test results were used to iden- tify advantages and limitations of these methods. Linear and 14 Table 4. Parametric experimental program. Aggregate type and MSA Type and content of binder w/cm Type M ix tu re N o. Crushed ¾ in. (19 mm) Crushed in. 3 8 (9.5 mm) Crushed ½ in. (12.5 mm) Gravel ½ in. (12.5 mm) Type I/II 809 pcy (480 kg/m3) Type III + 30% Slag 775 pcy (460 kg/m3) Type III + 20% fly ash 775 pcy (460 kg/m3) 0.33 0.38 1 x x x 2 x x x 3 x x x 4 x x x 5 x x x 6 x x x 7 x x x 8 x x x 9 x x x 10 x x x 11 x x x 12 x x x 13 x x x 14 x x x 15 x x x 16 x x x 17 x x x 18 x x x 19 x x x 20 x x x 21 x x x 22 x x x 23 x x x N on –a ir- en tra in ed (A E) co nc ret e 24 x x x 25- 27 Air entrainment of 4%–7% and slump flow of 26.0–27.5 in. (660–700 mm) w/cm of 0.33, Type III + 20% Class F fly ash, crushed aggregate with MSA of ½ in. (12.5 mm) 28- 30 Low filling ability, slump flow of 23.5–25.0 in. (600–635 mm) w/cm of 0.33, Type III + 30% slag, crushed aggregate with MSA of ¾ in. (19 mm) 31- 33 High filling ability, slump flow of 28.0–30.0 in. (710–760 mm) w/cm of 0.38, Type III + 30% slag, crushed aggregate with MSA of ¾ in. (19 mm) N on -A E co nc re te A E co n cr et e 34- 43 Two levels of slump flow consistency for evaluation of repeatability: 25.0 and 27.5 in. (635 and 700 mm) w/cm of 0.38, Type I/II, crushed aggregate with MSA of ½ in. (12.5 mm) Notes Sand–to–total aggregate ratio (S/A) is fixed at 0.50, by volume. PC-based HRWRA (AASHTO M 194, Type F) and air-entraining admixture (AASHTO M 154) are added. Limestone crushed coarse aggregate.

multiple regression analysis were used to relate the responses of various tests. Appropriate test methods that can be used to assess the workability of SCC in the laboratory and at the precast plant for quality control were proposed. Ranges of acceptance val- ues for these test methods were established. Non-standard test methods recommended for adoption as standard test methods are provided in Attachment C. Relationship Between Workability Measurements and Rheological Properties. The various test responses were related to plastic viscosity of the concrete using a concrete rheometer. “Workability boxes” identifying combinations of rheological parameters necessary to secure adequate stability of SCC were established for the SCC mixtures evaluated. Repeatability of Test Results. One mixture that exhib- ited good fluidity retention was used at two different slump flow levels (low and high) to establish the repeatability of the workability test methods. Each test was conducted five times, using different batches. Each test was performed by different operators. The data were used to develop precision statements. Phase 2: Effect of Mixture Proportioning and Material Characteristics on Key Parameters Affecting Fresh and Hardened Properties Limited information is available on the properties of hard- ened SCC mixtures typically used in precast, prestressed structural applications. Such properties can vary with the characteristics of constituent materials, including aggregate properties, type and composition of binder, and admixture combinations. Mixture composition and curing conditions necessary to secure the targeted strength for release of the pre- stressing also have a marked effect on engineering properties and durability of the SCC. The experimental work included non–air-entrained and air- entrained SCC mixtures. The targeted compressive strength at release of the prestressing strands for structural AASHTO-type girders was set at 5,000 psi (34.5 MPa) after 18 hours of casting. 15 Table 5. Experimental program of parametric investigation. SCC behavior Property Test Method Test age Number of samples per mixture Comments Rheology Yield stress and plastic viscosity Modified Tattersall MK III rheometer 10 & 40 minutes Not applicable Filling ability Slump flow and T-50(upright cone position) AASHTO T 119 10 & 40 minutes Not applicable Passing ability, filling capacity J-Ring, L-box, V-funnel flow, and caisson filling capacity ASTM C 1621 (for J-Ring) 10 & 40 minutes Not applicable Surface settlement Over the first 24 hours 1 Column segregation ASTM C 1610 10 minutes 1 Visual stability index ASTM C 1611 Not applicable Stability Stability of air* AASHTOT 152 Over 40 minutes Not applicable 18 hours 3 air cured 3 steam cured 28 days 3 moist curedCompressive strength AASHTOT 22 56 days 3 moist cured Mechanical properties Modulus of elasticity ASTM C 469 18 hours 2 steam cured Air curing at 50 ± 4% RH and 73 ± 4°F (23 ± 2°C) Moist curing at 100% RH and 73 ± 4°F (23 ± 2°C) Steam curing only for 16 hours * Agitation of concrete between 10 and 40 minutes at 6 rpm

The targeted 56-day compressive strength of the SCC mix- tures that were investigated in this study was 8,000 to 10,000 psi (55.2 to 69 MPa) determined on 4 × 8 in. (100 × 200 mm) cylinders moist cured at 100% relative humidity (RH) and 73 ± 4°F (23 ± 2°C). The specification of 56-day compressive strength is important when fly ash or ground granulated blast-furnace slag is incorporated in the SCC mixture because of the pozzolanic reaction. Non–Air-Entrained Concrete Mixtures. The experimen- tal factorial design presented in Table 6 was selected to eval- uate the influence of mixture proportioning and constituent material characteristics on the properties that are critical to the performance of precast, prestressed concrete girders. The effect of primary ingredients and mix design parameters on key workability and engineering properties of SCC was evaluated. Based on the literature review and findings of the parametric study, four mixture proportioning items and one ingredient type were considered in the experimental design. The factors included binder content, binder type, w/cm, S/A, and dosage of VMA. In total, 16 SCC mixtures were selected to form a factorial design with the following five main factors: • Binder content: 742 and 843 lb/yd3 (440 and 500 kg/m3) • w/cm: 0.34 and 0.40 • Dosage of thickening-type VMA: 0 and moderate dosage • Binder type: Type I/II and Type III cement with 20% Class F fly ash • S/A: 0.46 and 0.54, by volume The magnitude of these variables was selected to cover a wide range of mixture ingredients and designs used in the United States. The w/cm and binder type were selected based on the results of the parametric study. A low w/cm was in- cluded for better mechanical performance and the higher w/cm was included for better workability. Type III binder with 20% of Class F fly ash replacement was chosen over Type III binder with 30% slag because of its better overall performance in terms of workability and compressive strength development. 16 Table 6. Factorial experimental program. Coded values Absolute values Type MixNo. B in de r w /c m V M A a B in de r t yp e S/ A b B in de r lb /y d3 (kg /m 3 ) w /c m V M A B in de r t yp e S/ A 1 -1 -1 -1 -1 1 742 (440) 0.34 0 I/II 0.54 2 -1 -1 -1 1 -1 742 (440) 0.34 0 IIIc 0.46 3 -1 -1 1 -1 -1 742 (440) 0.34 moderate I/II 0.46 4 -1 -1 1 1 1 742 (440) 0.34 moderate III 0.54 5 -1 1 -1 -1 -1 742 (440) 0.40 0 I/II 0.46 6 -1 1 -1 1 1 742 (440) 0.40 0 III 0.54 7 -1 1 1 -1 1 742 (440) 0.40 moderate I/II 0.54 8 -1 1 1 1 -1 742 (440) 0.40 moderate III 0.46 9 1 -1 -1 -1 -1 843 (500) 0.34 0 I/II 0.46 10 1 -1 -1 1 1 843 (500) 0.34 0 III 0.54 11 1 -1 1 -1 1 843 (500) 0.34 moderate I/II 0.54 12 1 -1 1 1 -1 843 (500) 0.34 moderate III 0.46 13 1 1 -1 -1 1 843 (500) 0.40 0 I/II 0.54 14 1 1 -1 1 -1 843 (500) 0.40 0 III 0.46 15 1 1 1 -1 -1 843 (500) 0.40 moderate I/II 0.46 Fr ac tio na l f ac to ria l p oi nt s 16 1 1 1 1 1 843 (500) 0.40 moderate III 0.54 0 0 0 0 0 792 (470) 0.37 moderate I/II-III 0.50 0 0 0 0 0 792 (470) 0.37 moderate I/II-III 0.50 SC C (26 –2 7.6 in . [6 60 –7 00 m m] sl um p f low ) Ce nt ra l po in ts 0 0 0 0 0 792 (470) 0.37 moderate I/II-III 0.50 17 w/cm = 0.34, Type I/II cement, ½ in. (12.5 mm) crushed aggregate Normal consistency mixtures with 6 in. (150 mm) slump N on -A E co nc re te H PC 18 w/cm = 0.38, Type III + 20% Class F fly ash, ½ in. (12.5 mm) crushed aggregate Normal consistency mixtures with 6 in. (150 mm) slump A E co n cr et e SC C 19– 22 Air-entrainment of 4% to7% and slump flow of 26–27.6 in. (660–700 mm) Mixtures selected based on performance of non–air-entrained concrete a Thickening-type VMA b Crushed aggregate with MSA of ½ in. (12.5 mm) and natural sand c Type III cement + 20% Class F fly ash

The crushed coarse aggregate with a MSA of 1⁄2 in. (12.5 mm) was used because it offers better performance in terms of workability and strength development than gravel of similar MSA or crushed aggregate with 3⁄8 or 3⁄4 in. (9.5 or 19 mm). Three replicate central points were prepared to estimate the degree of experimental error for the modeled responses. In addition to the 16 SCC mixtures, two HPC mixtures of nor- mal consistency were evaluated. It should be noted that other mixture proportioning and material parameters (e.g., coarse aggregate shape and MSA, combined aggregate gradation, and sand type and fineness modulus) can also influence the performance of SCC. How- ever, only the most relevant factors were considered in the experimental program, as indicated in Table 7. Air-Entrained Concrete Mixtures. Four SCC mixtures were prepared to evaluate the effect of air-entrainment (4% to 7%) on fresh properties, fluidity retention, strength devel- opment, flexural strength, elastic modulus, air-void spacing fac- tor, and frost durability. These mixtures were selected based on results of the non–air-entrained concrete mixtures and were prepared with a selected combination of thickening-type VMA, polycarboxylate-based HRWRA, and a fixed S/A. Two concrete mixtures were prepared using two different binder types. The initial slump flow of the 16 fractional factorial and three central SCC mixtures was 26.0 to 27.5 in. (660 to 700 mm). The targeted release compressive strength after 18 hours of steam curing and 56-day compressive strength were 5,000 psi (34.5 MPa) and 8,000 to 10,000 psi (55 to 69 MPa), respec- tively. The compressive strength was determined on 4 × 8 in. (100 × 200 mm) cylinders. For 56-day compressive strength, the specimens were stored at 100% RH and 73 ± 4°F (23 ± 2°C) until the time of testing. The change in temperature in the chamber and in 4 × 8 in. (100 × 200 mm) reference cylinders during steam curing are presented in Attachment D. Test results were compared with the provisions for elastic- ity modulus, compressive strength, creep, drying shrinkage, and bond stipulated in several codes (AASHTO LRFD Spec- ifications [2004 and 2007]; Precast/Prestressed Concrete In- stitute (PCI) Bridge Design Manual 1997; ACI 209, ACI 318, CEB-FIP MC90, etc.). Formwork Pressure. The initial maximum pressure exerted by SCC and HPC was evaluated by casting concrete in rigid polyvinyl chloride (PVC) column measuring 3.6 ft (1.1 m) in height and 7.9 in. (200 mm) in diameter at a rate of 13 to 16 ft/h (4 to 5 m/h). Pressure sensors were installed at 2, 10, and 18 in. (50, 250, and 450 mm) from the bottom of the pressure decay tube. The sensors were set flush with the inner surface of the PVC column; the drilled holes through the PVC tubing were sealed to avoid leakage. The pressure sensors had a capacity of 25 psi (170 kPa), can operate over a temperature range of −58°F to 212°F (−50°C to 100°C), and were calibrated using a mechanical calibration instrument prior to use. Drop in lateral pressure was monitored until pressure cancellation (results are presented in Attachment D). Temperature Rise. Temperature rise was measured in a 6 × 12 in. (150 × 300 mm) concrete cylinder that was inserted at the center of a styrofoam box measuring 3.3 × 3.3 × 3.3 ft (1 × 1 × 1 m). Three thermo-couples were installed inside the concrete cylinders—one in the center of the cylinder, one in the middle height of the inner side of the cylinder, and one in the top of the inner side of the cylinder—to determine the temperature rise under semi-adiabatic conditions. Autogenous Shrinkage. Autogenous shrinkage was meas- ured on 3 × 3 × 11.8 in. (75 × 75 × 285 mm) prisms. The prisms were sealed immediately after removal from the molds at 18 hours of age and kept at 73 ± 4°F (23 ± 2°C) until the end of testing. Autogenous shrinkage was monitored using embedded vibrating wire strain gages until stabilization, which occurred after approximately 3 weeks of age. The autogenous shrink- age was obtained by subtracting the total shrinkage from thermal deformation. A linear thermal expansion coefficient of 6.4 µin./in./°F (11.5 µm/m/°C) was assumed for adjusting vibrating wire gage readings. The thermal expansion coefficient of the concrete was determined from the slope of the total deformation versus temperature curve of concrete prisms subjected to controlled temperature changes. Two prisms were initially immersed in water at the approximate temperature of 122°F (50°C). Once the temperature of the specimens was stabilized, the water was allowed to cool down to approxi- mately 68°F (20°C). The resulting deformations were used to estimate the coefficient of thermal expansion/contraction of the concrete. Drying Shrinkage and Creep. Six 6 × 12 in. (150 × 300 mm) test specimens were cast to monitor creep and drying shrinkage. The specimens were steam cured until the age of 16 hours and were then demolded. The ends of creep cylinders were ground and external studs were installed for deformation measure- ments. A digital-type extensometer was used to determine drying shrinkage and creep. Creep and shrinkage testing started at the age of 18 hours. The applied creep loading corresponded to 40% of the 18-hour compressive strength of the steam-cured concrete cylinders. Creep and shrinkage specimens were kept in a temperature-controlled room at 73 ± 4°F (23 ± 2°C) and 50% ± 4% relative humidity. Initial elastic deformations were measured directly after loading; creep and drying shrinkage deformations were monitored for 11 months; the long-term deformations were all stabilized at that time. Pull-out Bond Strength. Pull-out testing of prestressing strands was conducted for five SCC mixtures and one conven- tional concrete mixture. The SCC mixtures were proportioned with different viscosity and static stability levels. Tests were 17

18 Table 7. Factors considered in the testing program. SCC behavior Property Test method Test age Number of samples per mixture Comments Rheology Yield stress and plastic viscosity and thixotropy Modified Tattersall MK III rheometer 10 & 40 minutes Not applicable Filling ability Slump flow, T-50 (upright cone position) ASTM C 1611 10 & 40 minutes Not applicable J-Ring ASTM C 1621 Passing ability & filling capacity L-box, caisson filling capacity 10 & 40 minutes Not applicable Surface settlement Over the first 24 hours 1 Column segregation ASTM C 1610 1 Visual stability index ASTM C 1611 Not applicable Stability Stability of air* AASHTOT 152 Over 40 minutes Not applicable 18 hours 3 air cured 3 steam cured 7 days 3 moist cured 28 days 3 moist cured Compressive strength AASHTOT 22 56 days 3 moist cured 18 hours 2 air cured 2 steam cured 28 days 2 moist curedModulus of elasticity ASTM C 469 56 days 2 moist cured 7 days 3 moist cured 28 days 3 moist cured Mechanical properties Flexural strength AASHTOT 97 56 days 3 moist cured Air curing: 50 ± 4% RH, 73 ± 4°F (23 ± 2°C) Moist curing: 100% RH, 73 ± 4°F (23 ± 2°C) Steam curing: only for 14 hours (refer to Attachment D) * Agitation of concrete between 10 and 40 minutes at 6 rpm Temperature rise Over the first 24 hours 1 Semi-adiabatic conditions Hydration kinetics Setting time AASHTOT 197 1 Initial formwork pressure 2 to 4 hours 1 Form pressure characteristics Variation of pressure with time First 24 hours 1 Rate of rise of 13.1 to 16.4 ft/h (4 to 5 m/h) Autogenous shrinkage Embedded vibrating wire gages Over 10 to 14 days 2 Sealed prisms Drying shrinkage AASHTOT 160 Over 11 months 3 Same curing regime used for release strength Visco-elastic properties Creep ASTMC 512 Over 11 months 3 Loading at release time Air-void parameters ASTMC 457 Starting at 56 days 1 Frost durability Freezing and thawing resistance AASHTO T 161, Method A Starting at 56 days 2 Bond strength Pull-out load-end slip response 56 days 5 SCC & 1 HPC Air curing: at 50 ± 4% RH, 73 ± 4°F (23 ± 2°C)

conducted to determine the maximum pull-out load versus the end slip response of strands that were horizontally embedded in experimental wall elements. In total, 16 Grade 270, 0.6 in. (15.2 mm) diameter low-relaxation prestressing strands were embedded at four heights in 60.6 H × 84.6 L × 7.9 W in. (1,540 H × 2,150 L × 200 W mm) wall elements. Rigid plastic sheathing was tightly attached to the outer end of each strand near the loaded end as bond breaker to reduce secondary con- fining stresses along the bonded region. The formwork was removed 1 day after concrete casting. The concrete wall elements were then maintained under wet curing until 7 days of age before being air-dried. Pull-out tests were conducted at 56 days of age. The pull-out load was ap- plied gradually and recorded using a load cell; the net slip was measured using a linear voltage differential transducer (LVDT) connected to the unloaded end of the strand. Phase 3: Structural Performance of Full-Scale AASHTO-Type II Girders The structural performance of full-scale AASHTO precast, prestressed bridge girders constructed with selected SCC mix- tures was investigated to evaluate the applicability of current design provisions (AASHTO and PCI) and to recommend ap- propriate modifications to the AASHTO LRFD Specifications. The aspects studied were constructability, temperature varia- tions, transfer lengths, cambers, flexural cracking, shear crack- ing, and shear strengths. More details on the construction and testing of these girders are given in Attachment D. Two non–air-entrained SCC mixtures of different compres- sive strength levels were used to cast two full-scale AASHTO- Type II girders. One mixture had target 56-day compressive strength of 8,000 (55 MPa) and release strength of 5,000 psi (34.5 MPa) and the other had target compressive and release strengths of 10,000 psi (69 MPa) and 6,250 psi (43 MPa), respectively. Two additional girders were cast using HPC mixtures with target 56-day compressive strengths of 8,000 and 10,000 psi (55 and 69 MPa). The HRWRA dosages for the HPC and SCC mixtures were adjusted to obtain a slump of 6.3 ± 0.8 in. (160 ± 20 mm) and a slump flow of 26.8 ± 0.8 in. (680 ± 20 mm), respectively. The AASHTO-Type II girders have overall lengths of 31 ft (9.4 m) with center-to-center spans of 29 ft (8.8 m). The girders were prestressed with eight 0.6 in. (15.2 mm) diameter Grade 270 low-relaxation prestressing strands of six straight strands and two strands harped at double harping points located 4 ft 11 in. (1.5 m) from mid-span as shown in Figure 1. The pretensioning jacking system was calibrated to ensure ac- curate application of the force to each strand. The four mixes were proportioned with Type III cement and 20% Class F fly ash and crushed aggregate with MSA of 1⁄2 in. (12.5 mm), as presented in Table 8. 19 Figure 1. Details of precast pretensioned AASHTO-Type II girders. 6-0.6" strands 2-0.6" strands 48" 6.5" 36" 12" 3" 2" Section at ends Section at midspan 31'-0" total length 4'-11"9'-7"1'-0" 6"6" AASHTO Type II girder c

The testing program of the concrete used in the girders is presented in Table 9. For each girder, a minimum of fifty 4 × 8 in. (100 × 200 mm) cylinders and eighteen 3.9 × 3.9 × 15.7 in. (100 × 100 × 400 mm) beams were prepared. In total, 28 cylinders and nine flexural beams were match cured with the concrete girders. The rest of the cylinders and flexural beam specimens were demolded after 18 hours of air curing, then moist cured at 100% RH and 73.4°F (23°C) until testing. At the time of prestress release, three steam-cured and three air-cured cylinders were tested to determine the compressive strength. Four cylinders, two for each curing method, were used to determine the modulus of elasticity. The remaining steam- cured cylinders were stored near the girders and tested to 20 Table 8. Mixtures used for full-scale girders. Table 9. Concrete testing program for the girders. Concrete Targeted 56-day compressive strength Codification* (w/cm–binder content–binder type–S/A–VMA) 8,000 psi (55 MPa) 38-797-III20%FA (w/cm = 0.38, Type III cement + 20% Class F fly ash) HPC 10,000 psi (69 MPa) 33-793-III20%FA (w/cm = 0.33, Type III cement + 20% Class F fly ash) 8,000 psi (55 MPa) 38-742-III20%FA-S/A54 (w/cm = 0.38, Type III cement + 20% Class F fly ash, S/A = 0.54) SCC 10,000 psi (69 MPa) 32-843-III20%FA-S/A46-VMA (w/cm = 0.32, Type III cement + 20% Class F fly ash, S/A = 0.46) * ½ in. (12.5 mm) crushed aggregate for all mixtures SCC behavior Property Test method Test age Number of samples per mixture Size/volume of specimen Comments Rheology Yield stress, plastic viscosity Modified Tattersall MK III rheometer At arrival & after casting Not Not Not applicable applicable applicable Not applicable Not applicable 0.89 ft3 (25 l) Filling ability Slump flowa, T-50 (upright cone position) ASTM C 1611 At arrival & just after casting 0.11 ft3 (3.14 l) J-Ring ASTM C 1621Passing ability, filling capacity L-box, caisson filling capacity See Attachment D At arrival & after casting 2.54 ft3 (72 l) Surface settlement See Attachment D Over 24 hours 1 7.9 × 23.6 in. (200 × 600 mm) cylindrical specimens Column segregation ASTM C 1610 1 7.9 × 26 in. (200 × 660 mm) cylindrical specimens Visual stability index ASTM C 1621 0.11 ft 3 (3.14 l) Stability Stability of air AASHTOT 152 At arrival & after casting 0.25 ft3 (7 l) Autogenous shrinkage Embedded vibrating wire gages Over 1 month 2 3 × 3 × 11.2 in. (75 × 75 × 285 mm) prismbVisco- elastic properties Drying shrinkage AASHTOT 160 Over 6 months 3 6 × 12 in. (150 × 300 mm) cylinderc a Slump for HPC mixtures b Sealed prisms after demolding at release time c Same curing regime used for release strength

determine the compressive strength and modulus of elastic- ity at 7, 28, and 56 days, and also at the age corresponding to the time of testing the girders. The tests on beam specimens provided data on the modulus of rupture at the time of pre- stress release and at 28 and 56 days. 2.3 Approach for Relevant Changes to AASHTO LRFD Bridge Design and Construction Specifications To recommend relevant changes to AASHTO LRFD Bridge Design and Construction Specifications, the specification sections that relate to the proposed research were examined. Relevant changes are integrated in Attachment A. 2.4 Guidelines for Use of SCC in Precast, Prestressed Concrete Bridge Elements Based on the results of the literature survey and the labo- ratory evaluation, guidelines were developed for the use of SCC in precast, prestressed concrete bridge elements. The guidelines, provided in Attachment B, include information on the selection of material constituents, mixture propor- tioning, and testing of SCC. Performance-based specifica- tions of fresh and hardened concrete properties are provided, and special placement and construction issues are discussed. The guidelines deal with the early-age properties, mechanical properties, durability, and structural performance of SCC. 21 Table 9. (Continued). SCC behavior Property Test method Test age Number of samples per mixture Size/volume of specimen At release 3 steam cured 3 air cured 7 days 3 moist cured d 3 air curede 28 days 3 moist cured d 3 air curede 56 days 3 moist cured d 3 air curede Compressive strength AASHTO T 22 At shear testing 3 moist curedd 3 air curede 4 8 in. (100 200 mm) cylinders At release 2 steam cured 2 air cured 7 days 2 moist cured d 2 air curede 28 days 2 moist cured d 2 air curede 56 days 2 moist cured d 2 air curede Modulus of elasticity ASTM C 469 At shear testing 2 moist curedd 2 air curede 4 8 in. (100 200 mm) cylinders At release 3 steam cured 3 air cured 28 days 3 moist cured d 3 air curede Mechanical properties Flexural strength AASHTOT 97 56 days 3 moist cured d 3 air curede 3.9 3.9 15.7 in. (100 100 400 mm) prisms Temperature rise (semi-adiabatic conditions) 1 6 12 in. (150 300 mm) cylinders Hydration kinetics Setting time AASHTOT 197 1 Sieved mortar Transfer length, flexural cracking, and shear capacity 3-point flexural & shear testing 2 SCC girders 2 HPC girders Structural performance Camber growth 2 SCC girders 2 HPC girders Full-scale AASHTO-Type II girder with 31 ft (9.4 m) in length d18 hours of air curing followed by moist curing at 100% RH and 73°F (23°C) e18 hours of steam curing followed by air curing near the corresponding girderat 50 ± 4% RH and 73 ± 4°F (23 ± 2°C)

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 628: Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements explores recommended guidelines for the use of self-consolidating concrete (SCC) in precast, prestressed concrete bridge elements. The report examines the selection of constituent materials, proportioning of concrete mixtures, testing methods, fresh and hardened concrete properties, production and quality control issues, and other aspects of SCC.

Attachment D, “Research Description and Findings,” provides detailed information on the experimental program and data analysis, and the findings of the literature review.

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