Guidelines for Concrete Mixtures Containing Supplementary Cementitious Materials to Enhance Durability of Bridge Decks (2007) / Chapter Skim
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9Introduction The first task in determining the optimum concrete mixture for a particular application is to define what properties of the concrete are significant. This procedure requires differentiating between what properties are not relevant, what properties must meet but not necessarily exceed a minimum level of performance, and what properties are to be maximized (e.g., durability)
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10 SCM types, ranges for use, and effect on each property; and (4) other relevant mixture issues.
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guidance provided in this chapter. The recommended testing program based on the service environment of the hypothetical case study is summarized on this worksheet, which lists the properties of interest, the test methods to measure each property, and optimum target values that will be used to develop the desirability functions.
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Class C (high calcium) fly ashes show a higher rate of reaction at early ages than Class F fly ashes and typically do not result in a significant difference in compressive strength from pure portland cement concrete at replacements up to 30%.
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tensile strength measured with a splitting tensile test is approximately 500 psi (3.5 MPa) , while for 6000 psi (41.4 MPa)
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desired slump by increasing or decreasing the amount of HRWR, usually without adverse effects. Slump could be highly weighted (important)
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500 psi (3.5 MPa) , and final setting is attained at 4000 psi (27.6 MPa)
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and causing a plane of weakness (4)
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air void system are assessed after the concrete has hardened. The two primary methods for determining the plastic air content of concrete are AASHTO T 152 (ASTM C 231)
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Effect of SCMs on Air Content. The composition of the SCMs may have a significant influence on the effectiveness of air-entraining admixtures and the stability of the air voids in the plastic concrete.
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Desirability Functions for Freezing and Thawing Resistance. A durability factor of 100% corresponds to no decrease in relative dynamic modulus, suggesting no damage has occurred; performance that is as close to this level as possible is desired.
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concern of deicer salt scaling: a large concern, a moderate concern, or no concern. For severe and moderate deicer salt scaling environments, visual ratings of 0 to 1 and 2 to 3 at 50 cycles, respectively, are recommended.
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scaling performance whereas 50% might be a concern. ACI Committee 318 (32)
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combined. Measurements of water-soluble chloride approximate the amount of chloride that has permeated the concrete without including chemically bound, currently unavailable chloride.
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permeability should be minimized. ASTM C 1556 or the longterm AASHTO T 259 test method more realistically simulate the penetration mechanisms of chlorides in concrete that occur in bridge decks.
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Coastal Environments [CO1] Concerns about durability in coastal environments also include airborne-chloride exposure that can lead to corrosion problems in a manner similar to exposure to chloride from deicing salts as discussed previously in "Chloride Penetration Resistance." Direct contact with sea water in tidal zones is the most aggressive exposure; airborne-chloride exposure is less severe than tidal or deicer exposure.
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for this property may have to be modified to bracket the actual test results. However, Figures S1.19 and S1.20 give examples of desirability functions for mass loss and depth of wear as a starting point.
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following tests are used to evaluate some of these individual properties: • Drying Shrinkage: AASHTO T 160, ASTM C 157 • Tensile Strength: AASHTO T 198 • Flexural Strength: AASHTO T 97, AASHTO T 177 • Modulus of Elasticity: ASTM C 469 • Creep: ASTM C 512 • Heat of Hydration: CRD-C38 • Coefficient of Thermal Expansion: CRD-C39 or AASHTO TP 60 Restrained Shrinkage [CR2] Restrained shrinkage cracking is evaluated using AASHTO PP 34-99, Standard Practice for Estimating the Cracking Tendency of Concrete, or ASTM C 1581, Standard Test Method for Determining Age of Cracking and Induced Tensile Stress Characteristics of Mortar and Concrete Under Restrained Shrinkage.
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determine the relative likelihood of early concrete cracking and to aid in selection of concrete mixtures that are less likely to crack. The test method may also be modified to evaluate other factors that may affect cracking such as curing time, method, or temperatures.
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Another temperature-related concern for concrete is the phenomenon of delayed ettringite formation (DEF) , in which the formation of early-age ettringite is suppressed by high curing temperatures but ettringite reforms under moist conditions at some time later in the concrete's life, causing deleterious expansion and cracking.
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This decrease may result from the reduction in hydroxide ions available to react with the other SCMs. Low dosages of silica fume (i.e., 3% to 5%)
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concrete surface from the upwind side of the work is also very effective. Use of a commercial grade fog nozzle is required to provide broad coverage and produce a fine mist that does not damage the concrete by depositing drops of water on the surface.
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interaction between these properties is complex. Typically, high-early-strength concretes are particularly prone to cracking because little shrinkage has dissipated before the concrete has developed a high modulus and low creep properties.
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Worksheet for Step 1 Worksheet S1.1. Desired concrete performance and associated considerations for mixture proportioning.
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Figures for Step 1 Concrete Service Environment In a Freezing Climate?
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34 0 0.2 0.4 0.6 0.8 1 0 1000 2000 3000 4000 5000 6000 7000 8000 Compressive Strength (psi) De s ira bi lit y 0 0.2 0.4 0.6 0.8 1 0 2000 4000 6000 8000 10000 12000 Compressive Strength (psi)
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35 0 0.2 0.4 0.6 0.8 1 400 500 600 700 800 900 Modulus of Rupture (psi) De s ira bi lit y 0 0.2 0.4 0.6 0.8 1 0 2 4 6 8 10 12 Slump (in.)
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36 0 0.2 0.4 0.6 0.8 1 0 5 10 15 20 25 30 Initial Setting (hrs.) De s ira bi lit y 0 0.2 0.4 0.6 0.8 1 0 5 10 15 20 25 Finishability Rating De s ira bi lit y 0 0.2 0.4 0.6 0.8 1 0 2 4 6 8 10 12 14 Air Content (%)
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37 0 0.2 0.4 0.6 0.8 1 0.004 0.008 0.012 0.016 0.02 Spacing Factor De s ira bi lit y With HRWR, w/cm < 0.38 No HRWR 0 0.2 0.4 0.6 0.8 1 0 200 400 600 800 1000 Specific Surface Area (in2/in3) De s ira bi lit y 0 0.2 0.4 0.6 0.8 1 40 50 60 70 80 90 100 110 Freeze-thaw Durability Factor (%)
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38 0 0.2 0.4 0.6 0.8 1 40 50 60 70 80 90 100 110 Freeze-thaw Durability Factor (%) D e s ira bi lit y After 300 cycles After 500 cycles 0 0.2 0.4 0.6 0.8 1 0 1 2 3 4 5 Scaling Rating D e s ira bi lit y Severe Exposure Moderate Exposure 0 0.2 0.4 0.6 0.8 1 0 200 400 600 800 1000 1200 Scaling mass loss (g/m2)
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39 0 0.2 0.4 0.6 0.8 1 0 2 4 6 8 10 12 14 Apparent Chloride Diffusion Coefficient (x 10-12 m2/s) De s ira bi lit y 0 0.2 0.4 0.6 0.8 1 0 1000 2000 3000 4000 5000 6000 Charge Passed (Coulombs)
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40 0 0.2 0.4 0.6 0.8 1 0 0.5 1 1.5 2 2.5 Depth of wear after six mintues (mm) De s ira bi lit y 0 0.2 0.4 0.6 0.8 1 -0.12 -0.1 -0.08 -0.06 -0.04 -0.02 0 Shrinkage (% strain)
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41 0 0.2 0.4 0.6 0.8 1 0 20 40 60 80 100 Temperature Rise (°F) De s ira bi lit y 0 0.2 0.4 0.6 0.8 1 0 1 2 3 4 5 6 7 8 9 Modulus of Elasticity (x106 psi)
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42 Tables for Step 1 Environment Property/Test Method Range of Class C Fly Ash (%) Range of Class F Fly Ash (%)
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43 Property Recommendation Aggregate Good quality w/cm < 0.45 Minimum cement content 564 lbs/yd3 (335 kg/m3) Compressive strength when exposed to freezing Minimum 2,500 psi (17 MPa)
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Environment Property/Test Method Target Value for Test Method Range of Class C Fly Ash Range of Class F Fly Ash Range of GGBFS Range of silica fume Range of other SCM w/cm Aggregate restrictions Specified aggregate top size Specified cement content Other requirements Compressive strength: AASHTO T 22, ASTM C 39 Flexural strength: AASHTO T 177, T 97, or T 198, ASTM C 293, C 78, or C 496 Slump and slump loss: AASHTO T 119, ASTM C 143 Time of setting: AASHTO T 197, ASTM C 403 Universal performance requirements Finishability Chloride penetration: AASHTO T 259, ASTM C 1566 Electrical conductivity: AASHTO T 277, ASTM C 1202 Freezing and thawing with chemical deicers Scaling resistance: ASTM C 672 Air content, %: ASTM C 457 Spacing factor: ASTM C 457 Freezing and thawing without chemical deicers Freezing and thawing resistance: AASHTO T 161 A, ASTM C 666 A Chloride penetration: AASHTO T 259, ASTM C 1566 Coastal Electrical Conductivity: AASHTO T 277, ASTM C 1202 Abrasive Abrasion: ASTM C 944 or C 779 Procedure B Cracking resistance: ASR Go to Raw Materials Flowchart Restrained ring cracking: AASHTO PP 34-99, ASTM C 1581 Cracking resistance: restrained shrinkage Free drying shrinkage: AASHTO T 160, ASTM C 157 Heat of hydration Cracking resistance: thermal concerns Modulus of elasticity, ASTM C 469 Cracking resistance: plastic shrinkage Plastic shrinkage cracking: ICC AC32 Annex A Other design requirements SUMMARY Table S1.8. Completed Worksheet S1.1 for the Hypothetical Case Study.
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