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CON 124 Session 4 - Proportioning Methods


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CON 124 - Proportioning Methods
O. Tavares

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CON 124 Session 4 - Proportioning Methods

  1. 1. CON 124 Basic Concrete Mix Design Proportioning Session 4 Proportioning Methods
  2. 2. Methods for Proportioning Concrete Mixtures  Water-cement ratio method  Weight method  Absolute volume method  Field experience (statistical data)  Trial mixtures
  3. 3. Design of Concrete Mixtures  Establishment of specific concrete characteristics  Relative Density (Specific Gravity)  Absolute volume calculation (27 Cubic Ft)  Durability Issues  Selection of proportions of available materials to produce concrete of required properties, with the greatest economy
  4. 4. Concrete Mixture Design from Field Data  Strength-Test Data  Standard Deviations show mixture is acceptable  Durability aspects must be met  Statistical data should represent the same material, proportions, and concreting conditions
  5. 5. Proportioning Data for Proposed Work  Concrete Strength within 7MPa (1000 psi)  Data should represent at least 30 consecutive tests or two groups representing of consecutive tests totaling at least 30 tests (average of two cylinders)  If data between 15-29 tests, an adjusted Std. Dev. (S) is multiplied by modification factor from Table 11  Modified Std. Dev. (S) is then used in equations 1-3 from Table 12  When field strength test records do not meet the above, then the required average strength of concrete can be obtained from Table 13 (Table 9-11)
  6. 6. Proportioning from Field Data Number of tests Modification factor for standard deviation Less than 15 see next slide 15 1.16 20 1.08 25 1.03 30 or more 1.00 Modification Factor for Standard Deviation ( 30 Tests) Table 11: Modification factor for standard deviation when less than 30 tests are available. Interpolated for design mixtures modified standard deviation to be used to determine required average strength. Adapted from ACI 318.
  7. 7. Proportioning from Field Data Required Strength When Data Are Available to Establish a Standard Deviation Specified compressive strength, f'c, psi Required average compressive strength, f'cr, psi 5000 f'cr = f'c+ 1.34s f'cr = f'c + 2.33s - 500 Use larger value Over 5000 f'cr = f'c+ 1.34s f'cr = 0.90f'c + 2.33s Use larger value Inch-Pound Table 12: Required Average Compressive Strength When Data Are Available to Establish a Standard Deviation (Inch-Pound) Adapted from ACI 318.
  8. 8. Proportioning from Field Data Required Strength When Data Are Not Available to Establish a Standard Deviation Specified compressive strength, f'c, psi Required average compressive strength, f'cr, psi Less than 3000 f'c + 1000 3000 to 5000 f'c + 1200 Over 5000 1.10f'c + 700 Inch-Pound Table 13: (Inch-Pound Units). Required Average Compressive Strength When Data Are Not Available to Establish a Standard Deviation Adapted from ACI 318.
  9. 9. Proportioning by Trial Mixtures  Trial batching verifies that a concrete mixture meets design requirements prior to use in construction.  The trial mixtures should use the same materials proposed for the work.  Three mixtures with three different water-cementing materials ratios or cementing materials contents should be made.  The trial mixtures should have a slump and air content within ±20 mm (±0.75 in.) and ± 0.5%, respectively, of the maximum permitted.  Three cylinders for each water-cementing materials ratio should be tested at 28 days.
  10. 10. Proportioning by Trial Mixtures  Approved mixture must meet required average compressive strength  Three trial mixtures using three different water to cementing materials ratios  Slump and Air Content within +/- 20 mm(+/- 0.75 in.) and +/- 0.5%  Cylinders cured as per ASTM C192 (AASHTO T126)  Plot water to cementing ratio to strength curve  Test the properties of the newly proportioned mixture
  11. 11. Proportioning Concrete Ingredients  Arbitrary assignment (1:2:3), volumetric  Void Ratio  Fineness Modulus  Surface Area of Aggregates  Cement Content  Best approach  Select proportions based on past experience  Reliable test data established relationship between strength and water to cementing materials ratio
  12. 12. Plotting of Water to Cementing Ratio to Compressive Strength
  13. 13. Satisfactory Job Mixture  Required Strength  Minimum Cementing Materials Content or Maximum Water to Cementing Materials Ratio  Nominal Maximum Size Aggregate  Necessary Amounts of Fine and Coarse Aggregate (saturated surface dry condition, SSD)  Air Content  Desired Slump
  14. 14. Saturated Surface-Dry Density (SSD-Density) where DSSD is density in the SSD condition M1 is the SSD mass in air, kg (lb) M2 is the apparent mass immersed in water, kg (lb) is the density of water, 1000 kg/m3 (62.4 lb/ft3) 21 1 MM M DSSD
  15. 15. Slump Test Slump test for consistency of concrete. Left figure illustrates a lower slump, right figure a higher slump.
  16. 16. Air Content Pressure method ASTM C 231 (AASHTO T 152) Volumetric method ASTM C 173 (AASHTO T 196) Air indicator method AASHTO T 199
  17. 17. Tests, Measurements, Calculations  Tests for slump, air content, and temperature on trial mixture  Density (Unit Weight) and Yield  Absolute Volume
  18. 18. Density (Unit Weight), Yield  In accordance with ASTM C138  Density (Unit Weight): Pounds/Cubic ft  Yield: Cubic Feet  Calculation, Dividing total mass of materials batched to density of freshly mixed concrete
  19. 19. Density (Unit Weight) and Yield Fresh concrete is measured in a container of known volume to determine density (unit weight) • Scale must be sensitive to 0.3% of anticipated mass of sample and container • Size of container varies according to the size of the aggregate, the 7-L (25-ft3) air meter container for up tp 25-mm (1-in.) nominal max. size aggregate: 14-L (0.5 ft3) container for aggregates up to 50 mm (2-in.) • Container should be calibrated at least annually (ASTM C 1077)
  20. 20. Density (Unit Weight) and Yield ASTM C 138 (AASHTO T 121) Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete ASTM C 1040 (AASHTO T 271) • Density of Unhardened and Hardened Concrete in Place By Nuclear Methods
  21. 21. Absolute Volume  Volume of a granular material is the volume of the solid matter in the particles without volume of air spaces  Yield of freshly mixed concrete is equal to the sum of the absolute volumes of the concrete ingredients
  22. 22. Proportioning Concrete Mixtures Absolute Volume Method Dry Rodded Density Absolute Volume Density
  23. 23. Proportioning Concrete Mixtures Absolute Volume Method Abs Vol Density = Weight/Volume (no voids) Specific Gravity = Abs Vol Density / Density of Water Vol
  24. 24. Proportioning Concrete Mixtures Absolute Volume Method Abs Vol=Wt/(Specific Gravity x Density of Water) Weight=Abs Vol x Specific Gravity x Density of Water Density of Water = 62.4 lbs per cu ft ( @ 40C)
  25. 25. Material Density Values  Portland Cement Relative Density (Specific Gravity) value: 3.15  Blended Cements Relative Density Ranges: 2.90 to 3.15  Fly Ash Relative Density value: 1.9 to2.8  Slag Relative Density value: 2.85 to 2.95  Water Relative Density value: 1.0  Normal Aggregates Relative Density value: 2.4 to 2.9
  26. 26. Design Review Flowchart
  27. 27. Design Review Flowchart
  28. 28. Design Review Flowchart
  29. 29. Design Review Flowchart
  30. 30. Questions? Email