CON 124 Session 2 - Proportioning Methods

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  • 1. CON 124Basic Concrete Mix Design ProportioningSession 2Proportioning Methods
  • 2. Methods for Proportioning Concrete Mixtures Water-cement ratio method Weight method Absolute volume method Field experience (statistical data) Trial mixtures
  • 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. 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. 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. Table 11: Proportioning from Field Data 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. Table 11: Proportioning from Field Data Modification factor forNumber of tests 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)
  • 8. Table 12: Proportioning from Field Data Required Strength When Data Are Available to Establish a Standard Deviation Specified compressive Required average strength, fc, psi compressive strength, fcr, psi fcr = fc+ 1.34s  5000 fcr = fc + 2.33s - 500 Use larger value fcr = fc+ 1.34s Over 5000 fcr = 0.90fc + 2.33s Use larger valueInch-Pound Adapted from ACI 318
  • 9. Table 13: Proportioning from Field Data Required Strength When Data Are Not Available to Establish a Standard Deviation Specified compressive Required average strength, compressive strength, fc, psi fcr, psi Less than 3000 fc + 1000 3000 to 5000 fc + 1200 Over 5000 1.10fc + 700Inch-Pound Adapted from ACI 318
  • 10. Proportioning by Trial MixturesTrial batching verifies that a concrete mixture meetsdesign requirements prior to use in construction.
  • 11. Proportioning by Trial Mixtures 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.
  • 12. 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
  • 13. 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
  • 14. Plotting of Water to Cementing Ratio to Compressive Strength
  • 15. 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 15
  • 16. Saturated Surface-Dry Density (SSD-Density) M1 DSSD  M1  M 2 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)
  • 17. Slump Testlower slump higher slump
  • 18. Air Content Pressure method ASTM C 231 (AASHTO T 152) Volumetric method ASTM C 173 (AASHTO T 196) Air indicator method AASHTO T 199 18
  • 19. Tests, Measurements, Calculations Tests for slump, air content, and temperature on trial mixture Density (Unit Weight) and Yield Absolute Volume
  • 20. 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
  • 21. 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)
  • 22. 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
  • 23. 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
  • 24. Proportioning Concrete MixturesAbsolute Volume MethodDry Rodded Density Absolute Volume Density
  • 25. Proportioning Concrete MixturesAbsolute Volume Method VolAbs Vol Density = Weight/Volume (no voids) Specific Gravity = Abs Vol Density / Density of Water
  • 26. Proportioning Concrete MixturesAbsolute Volume Method Abs Vol=Wt/(Specific Gravity x Density of Water) Weight=Abs Vol x Specific Gravity x Density of WaterDensity of Water = 62.4 lbs per cu ft ( @ 40C)
  • 27. 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
  • 28. Design Review Flowchart