Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements (2009) / Chapter Skim
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Attachment A - Recommended Changes to AASHTO LRFD Bridge Design and Construction Specifications
Attachment A - Recommended Changes to AASHTO LRFD Bridge Design and Construction Specifications
Pages 32-41
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From page 32... ...
A-1 A T T A C H M E N T A Recommended Changes to AASHTO LRFD Bridge Design and Construction Specifications These proposed changes to AASHTO LRFD Bridge Design and Construction Specifications are the recommendations of the NCHRP Project 18-12 staff at the University of Sherbrooke. These specifications have not been approved by NCHRP or any AASHTO committee nor formally accepted for the AASHTO specifications.
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From page 33... ...
A-3 C O N T E N T S A-4 A.1 Bridge Design Specifications A-4 A.1.1 Mixture Characteristics A-4 A.1.2 Code Provisions for Mechanical and Visco-Elastic Properties A-5 A.2 Construction Specifications A-5 A.2.1 Classification A-6 A.2.2 Material Constituents A-7 A.2.3 Mix Design and Proportioning A-9 A.2.4 Production, Handling, and Placement
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From page 34... ...
Specifications Commentary Minimum Cement Content Maximum W/C w/cm Ratio Air Content Range Coarse Aggregate Per AASHTO M 43 (ASTM D 448) 28-day Compressive Strength 56-day Compressive StrengthClass of Concrete pcy lbs.
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From page 35... ...
Clause 5.4.2.3.3 Drying Shrinkage For steam cured concretes devoid of shrinkage-prone aggregates, the strain due to shrinkage, sh, at time, t, may be taken as: where: t = drying time (day) ks = size factor kh = humidity factor V / S = volume-to-surface ratio, and A = cement factor: 0.918 for Type I/II cement and 1.065 for Type III + 20% FA binder which may be used for P(SCC)
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From page 36... ...
designated for precast, prestressed bridge elements. Supplementary cementitious materials can be incorporated to replace part of the cement; for example, 20 percent Class F fly ash or 30 percent slag can be used as part of the total mass of binder for P(SCC)
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From page 37... ...
In designing P(SCC) , a number of factors should be taken into consideration to a greater degree than when designing conventional vibrated concrete: • Properties of locally available raw materials, including mineral, geometric, and physical properties of aggregates and cementitious materials Specifications Commentary
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From page 38... ...
at the time of placement. A-8 • Need for higher level of quality control, greater awareness of aggregate gradation, and better control of mix water and aggregate moisture • Choice of chemical admixtures and their compatibilities with the selected binder • Consideration of placement technique, configuration of cast element, and environmental conditions Clause C8.4.2 For P(SCC)
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From page 39... ...
In some cases, limestone filler may be used to replace part of the portland cement or to increase the powder content of SCC. Selected fillers should be uniform in chemical composition and physical characteristics and should not hinder the targeted performance of SCC (workability, strength development, and durability)
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From page 40... ...
concrete, any concrete represented by a test that indicates a strength that is less than the specified compressive strength at the specified age will be rejected and shall be removed and replaced with acceptable concrete. Clause 8.7 HANDLING AND PLACING CONCRETE Clause 8.7.3 Placing Methods Clause 8.7.3.1 General Because SCC is based on concrete placement without vibratory consolidation, an adequate construction plan should be formulated in consideration of the properties specific to SCC so that the proportioned concrete could be transported and placed while the required self-consolidation is retained.
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From page 41... ...
A-11 Specifications Commentary Placement Technique Discharge Rate Discharge Type Single Discharge Volume Flow Momentum Rating Truck Chute High Continuous High High Pump Medium/High Continuous Medium High/Medium Conveyor Medium Continuous High High Buggy Medium Continuous Low Low Crane and Bucket High Discontinuous Low Low/Medium Auger Low Continuous Medium Medium Drop Tube High Discontinuous High High Table C8.7.3-1. Relative placement energy associated with different placement techniques for SCC (Daczko and Constantiner, 2001)
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