Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements (2009) / Chapter Skim
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Attachment B - Recommended Guidelines for Use of Self-Consolidating Concrete in Precast, Prestressed Concrete Bridge Elements
Attachment B - Recommended Guidelines for Use of Self-Consolidating Concrete in Precast, Prestressed Concrete Bridge Elements
Pages 42-78
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From page 42... ...
B-1 A T T A C H M E N T B Recommended Guidelines for Use of Self-Consolidating Concrete in Precast, Prestressed Concrete Bridge Elements These proposed guidelines are the recommendations of the NCHRP Project 18-12 staff at the University of Sherbrooke. These guidelines have not been approved by NCHRP or any AASHTO committee nor formally accepted for adoption by AASHTO.
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From page 43... ...
B-5 Introduction B-6 Glossary B-9 B.1 Guidelines for Selection of Constituent Materials B-9 B.1.1 General B-9 B.1.2 Cement and Cementitious Materials B-9 B.1.2.1 Cement and Blended Cement B-10 B.1.2.2 Fly Ash B-10 B.1.2.3 Silica Fume B-10 B.1.2.4 Ground Granulated Blast-Furnace Slag B-11 B.1.2.5 Fillers B-11 B.1.2.6 Other Supplementary Cementitious Additions B-11 B.1.3 Aggregate Characteristics B-11 B.1.3.1 Coarse Aggregate B-12 B.1.3.2 Fine Aggregate B-12 B.1.4 Chemical Admixtures B-12 B.1.4.1 High-Range Water-Reducing Admixtures B-13 B.1.4.2 Viscosity-Modifying Admixtures B-13 B.1.4.3 Air-Entraining Admixtures B-13 B.1.4.4 Set-Retarding and Set-Accelerating Admixtures B-13 B.1.4.5 Shrinkage-Reducing Admixtures B-14 B.1.4.6 Other Admixtures B-14 B.1.5 Fibers B-14 B.2 Guidelines for Selection of Workability Test Methods B-14 B.2.1 General B-14 B.2.2 Filling Ability B-14 B.2.2.1 Significance B-15 B.2.2.2 Test Methods to Assess Filling Ability B-15 B.2.2.3 Special Issues B-16 B.2.3 Passing Ability B-16 B.2.3.1 Significance B-16 B.2.3.2 Test Methods to Assess Passing Ability B-16 B.2.3.3 Special Issues B-16 B.2.4 Filling Capacity B-16 B.2.4.1 Significance B-17 B.2.4.2 Test Method to Assess Filling Capacity B-17 B.2.4.3 Special Issues B-18 B.2.5 Static Stability B-18 B.2.5.1 Significance B-18 B.2.5.2 Test Methods to Assess Static Stability B-18 B.2.5.3 Special Issues C O N T E N T S B-3
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From page 44... ...
B-18 B.2.6 Dynamic Stability B-18 B.2.6.1 Significance B-18 B.2.6.2 Test Methods to Assess Dynamic Stability B-19 B.2.7 Rheology B-19 B.2.7.1 Significance B-19 B.2.7.2 Test Methods to Assess Rheological Parameters B-19 B.2.7.3 Special Issues B-20 B.3 Guidelines for Mix Design B-20 B.3.1 General B-20 B.3.2 Mix Design Principles B-22 B.3.2.1 Minimum Free Water Content B-22 B.3.2.2 Moderate Water Content and Medium Concentration of VMA B-22 B.3.2.3 Low Water Content and Low Concentration of VMA B-22 B.3.3 Cementitious Materials Content and Water-Cementitious Material Ratio B-22 B.3.4 Nominal Size of Coarse Aggregate B-23 B.3.5 Air-Entrainment and Air-Void Stability B-23 B.3.6 Mixture Robustness B-23 B.3.7 Trial Batches B-23 B.3.8 Recommended Range of Workability Characteristics B-24 B.3.9 Quality Confirmation of SCC B-26 B.4 Guidelines for Early-Age and Hardened Properties B-26 B.4.1 General B-26 B.4.2 Setting B-26 B.4.3 Temperature Development B-27 B.4.4 Release Compressive Strength B-28 B.4.5 Flexural Strength B-28 B.4.6 Modulus of Elasticity B-29 B.4.7 Creep B-30 B.4.8 Autogenous Shrinkage B-30 B.4.9 Drying Shrinkage B-31 B.4.10 Durability and Air-Void System B-32 B.4.11 Bond to Prestressing Strands B-33 B.5 Guidelines for Production and Control B-33 B.5.1 General B-33 B.5.2 Control of Raw Materials B-34 B.5.3 Mixing Process and Sequence B-34 B.5.4 Transport B-34 B.5.5 Site Acceptance of Plastic Concrete B-34 B.5.6 Placement Techniques and Casting Considerations B-35 B.5.7 Temperature Control B-36 B.5.8 Formwork Considerations and Lateral Pressure B-36 B.5.9 Finishing B-36 B.5.10 Curing B-38 References B-4
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From page 45... ...
The flowability of SCC is higher than that of normal high-performance concrete typically used in precast, prestressed concrete plants. This characteristic of SCC, coupled with the absence of the noise associated with vibration, make SCC a desirable material for fabricating prestressed bridge elements.
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From page 46... ...
. Blocking -- The condition in which coarse aggregate particles combine to form elements large enough to obstruct the flow of the fresh concrete between the reinforcing steel or other obstructions in the concrete formwork (PCI 2003)
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. In the context of SCC, rheology refers to the evaluation of yield stress, plastic viscosity, and thixotropy to achieve desired levels of filling ability, passing ability, and segregation resistance.
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. For SCC, workability encompasses filling B-8 ability, passing ability, and segregation resistance, and it is affected by rheology.
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The total content of cementitious materials used in prestressed concrete for a 28-day design compressive strength of 4,000 to 8,000 psi (28 to 55 MPa) can vary from 600 to 1,000 lb/yd3 (356 to 593 kg/m3)
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. B.1.2.2 Fly Ash Pozzolans and slag meeting ASTM C 618, C 989, or C 1240 are supplementary cementitious material and may be added to portland cements during mixing to produce SCC with improved workability, increased strength, reduced permeability and efflorescence, and improved durability.
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. B.1.3.1 Coarse Aggregate Unless otherwise specified in the contract documents, the recommendation is to use normal-density coarse aggregate meeting the requirements of AASHTO M 80 or ASTM C 33.
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Grading requirements for fine aggregates. B.1.4 Chemical Admixtures Chemical admixtures are used in precast, prestressed concrete to reduce water content, improve filling ability and stability, provide air entrainment, accelerate strength development, enhance workability retention, and retard setting time.
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Starting with a low dosage rate of VMA, the rate should be gradually increased to establish the dosage rate that provides the desired level of stability. VMA should not be added to SCC as a means for improving a poor mix design or poor selection of materials.
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In general, test methods include the components required for evaluating simultaneously the filling ability, passing ability, and static stability. Table B.2 summarizes some of the main test methods proposed for the evaluation of workability of SCC.
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This test is called T-50 flow time. Test methods Applicable standard Filling ability Slump flow and T-50 ASTM C 1611 L-box J-Ring ASTM C 1621 Passing ability V-funnel Filling capacity Combining filling and passing abilities Surface settlement Column segregation ASTM C 1610 Static stability Visual stability index ASTM C 1611 Slump flow Advantages Precautions o Simple o Reproducible o Results correlate to yield stress o Low sensitivity to water content o Can be performed by a single operator o Roughness and moisture of base plate affect results o Large base plate is required to perform test o Must be performed on level surfaces T-50 o Results correlate to plastic viscosity o Can be performed simultaneously with slump flow using a second operator o Sensitive to roughness and moisture of base plate o Poor single- and multi-operator repeatability o High error for low-viscosity mixtures
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From page 56... ...
B.2.4 Filling Capacity B.2.4.1 Significance The property to completely fill intricate formwork or formwork containing closely spaced obstacles is critical for SCC to achieve adequate in-situ performance. SCC with high In general, the maximum difference between slump flow and J-Ring flow varies from 2 to 3 in.
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From page 57... ...
J-Ring Advantages Precautions o Simple o Good repeatability o Can be performed by a single operator o Material segregation can be visually detected o Roughness and moisture of base plate affect results o Large base plate is required to perform the test o Must be performed on level surfaces L-box o Good repeatability o Can be performed by a single operator o Flow time correlates to plastic viscosity o Must be performed on level surfaces V-funnel o Can be performed by a single operator o Flow time correlates to plastic viscosity o Poor repeatability o Risk of flow interruption in high-viscosity mixtures Filling capacity Advantages Precautions o Good repeatability o Good indicator of filling capacity, which combines filling ability and passing ability of SCC o Visual appreciation of filling capacity through congested sections o Difficult to perform by single operator o Requires some calculation to evaluate filling capacity
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Concrete with high filling ability (deformability) and good passing ability can achieve adequate filling capacity in restricted and congested sections that are typical precast, prestressed B-18 Guidelines Commentary
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applications. An adequate combination of filling and passing ability tests can be used to evaluate the filling capacity of the concrete, which is indicative of the dynamic stability.
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For mix design approval, a minimum of three test cylinders are taken from a trial batch. The average compressive strength shall be at least 1,200 psi (8.3 MPa)
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In principle, three approaches can be used for the production of SCC: • Increase of the ultra-fines content by using fly ash, blastfurnace slag, limestone filler (powder type) , and in some cases low content of silica fume • Use of suitable viscosity-modifying admixture (VMA)
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From page 62... ...
A robust mixture can react less sensitively to fluctuations in the mixture composition, characteristics of the raw materials, water content, and concrete temperature. Special care should be taken to select the binder composition of the SCC made with low w/cm to limit the compressive strength to the target value.
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The following information shall be included in the trial batch data: • Source of all materials • Specific gravity and gradation results for sand and coarse aggregate • Design slump flow range • Target air content and design strength • Details of mixture proportioning, including admixture dosage rates for design slump flow range • SCC trial mixture test results for QC testing • Mixer used for the mix design, mixing sequence, charging sequence, and mixing time B.3.8 Recommended Range of Workability Characteristics The use of proven combinations of test methods and performance-based specifications is necessary to reduce time SCC mixtures are more sensitive to the variations in the properties and conditions of constituent materials and quantity fluctuations during production. Fluctuations in raw materials, such as gradations and moisture contents of aggregates, and batching fluctuation can have dramatic influence on the flowability and the stability of the concrete.
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From page 64... ...
0.5–1.0 Filling capacity 70%–100% Slump flow and J-Ring flow tests Filling capacity Slump flow and L-Box tests Surface settlement Rate of settlement, 25–30 min (value can decrease to 10–15 min)
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For mix design qualification of hardened properties, B-25 Guidelines Commentary Table B.9. Workability values of SCC used in precast/prestressed applications.
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The difference between initial and final setting time (ASTM 403–05) can range between 1 and 3 hours for SCC used in precast, prestressed applications proportioned with w/cm of 0.34 and 0.40, and Type I/II cement or Type III cement with 20% of fly ash replacement [Khayat et al., 2007]
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The use of VMA can increase the HRWRA demand and could lead to reduction in early strength development. Type III cement with supplementary cementitious materials (for example 20% of fly ash or 30% slag)
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; t1 = 1 day. 16 non-AEA SCC + 4 AEA SCC + 2 HPC: s = 0.19 Type I/II cement; R2 = 0.95 s = 0.20 Type III + 20% FA; R2 = 0.92 16 non–air-entrained SCC: s = 0.20 Type I/II cement; R2 = 0.95 s = 0.23 Type III + 20% FA; R2 = 0.93 B.4.5 Flexural Strength For precast and structural civil engineering applications, SCC mixtures are typically proportioned with relatively low w/cm of 0.32 to 0.36 and with supplementary cementitious materials and fillers and are expected to achieve higher flexural strength and flexural-to-compressive ratio than conventional slump concrete [ACI Committee 237, 2007]
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Creep behavior is related to the compressive strength of the matrix, coarse aggregate type, relative content of aggregate, as well as magnitude of applied load and age of loading. Creep takes place in the cement paste and is influenced by the capillary porosity of the paste.
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Higher surface area of the cement can activate the reactivity of the binder, hence increasing the degree of autogenous shrinkage. B.4.9 Drying Shrinkage In prestressed applications, shrinkage should be considered in the mix design and taken into consideration in the structural design of the member.
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εs = drying shrinkage obtained from RH-shrinkage chart βsc = cement type factor βRH = relative humidity factor fcm = mean 28-day compressive strength (MPa) Ac = cross-sectional area (mm2)
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From page 72... ...
As indicated in Table B.10, in order to secure adequate static stability, the SCC should have maximum surface settlement of 0.5%, column segregation index of 5%, or percent static segregation of 15%. critical to incorporate an AEA in concrete subjected to moderate frost exposure conditions to secure stable and closely spaced air bubbles (adequate spacing factor)
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From page 73... ...
The moisture content in coarse aggregate must be also taken into account and should be determined at least twice a day, at the beginning of the first and second production shifts. When designing SCC, some factors should be taken into consideration to a greater degree than when designing conventional concrete to ensure good filling capacity, such as the geometry configuration of cast elements and placement conditions.
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Mixing equipment and mixing sequence should be validated by testing consistency and self-consolidation properties for a given mix design. Necessary adjustments to time and speed of mixing should be carried out until consistent and compliant results are obtained.
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B.5.7 Temperature Control The mix design should be tailored to achieve the targeted properties specified in the performance specifications. When the use of steam curing is required to achieve the targeted early-age strength, the temperature of the concrete should not exceed 160°F (71°C)
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. Because of the relatively higher content of fines and eventual presence of VMA, SCC mixtures develop little or no bleed water compared with conventional concrete.
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. Due to the specification in terms of early-age compressive strength, steam curing or radiant heat curing can be used for precast concrete members.
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(1992) , "Role of Powder Materials on the Filling Capacity of Fresh Concrete," Supplementary Papers, 4th CANMET/ACI International Symposium on Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, Istanbul, pp.
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