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Portland Cement Concrete Module #10

Portland Cement Concrete Module #10. Prepared by Dr. Randy R. Rapp July 2005. Cements and Admixtures. Cements Types I through V, p. 250 Special purpose, p. 251 Admixtures Accelerators and retarders Plasticizers Air entrainment Water reduction Corrosion inhibiters

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Portland Cement Concrete Module #10

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  1. Portland Cement ConcreteModule #10 Prepared by Dr. Randy R. Rapp July 2005

  2. Cements and Admixtures • Cements • Types I through V, p. 250 • Special purpose, p. 251 • Admixtures • Accelerators and retarders • Plasticizers • Air entrainment • Water reduction • Corrosion inhibiters • Beware possible adverse interaction; a few % matter 2005, Randy R. Rapp

  3. Temperature Effects • Lower temperature slows hydration • Higher temperature speeds hydration • Water or aggregate can be artificially heated or cooled • Freezing during first day or two is devastating • Shrinkage may exceed tensile strength: saw joints 2005, Randy R. Rapp

  4. Water: Strength vs. Slump • Little water for hydration; most for workability • Water-cement ratio, w/c: • Extremely critical for strength: lower is better • Determined mainly by amount water/sack cement • Δ1 gal/sack cement = Δ500 to 1,000 lb/in2 (psi) • Slump • Indicates (does not measure) consistency • Match to formwork and reinforcement configuration • Determined mainly by amount of water per yd3 • Δ1 gal/yd3 concrete = Δ1-in slump 2005, Randy R. Rapp

  5. Steel Reinforcement • Types • Bars • Welded wire fabric (WWF) • Accessories • Bolsters and chairs • Ties and clips 2005, Randy R. Rapp

  6. Inspection Before Placement • Plant • Consistency • Mix materials: tests, p. 264 • Batching and mixing equipment • Pre-stressed members • Reports, p. 268 2005, Randy R. Rapp

  7. Inspection Before Placement (Cont’d) • Site • Reinforcement • Surface condition • Strength • In-place configuration and fastening • Foundation, Table 10-9 • Formwork, Table 10-10 • Commercial, reusable systems • Job-built • Timely correction is critical 2005, Randy R. Rapp

  8. Inspection During Placement • Checklist, Table 10-12 • Delivery: adequate trucks, tools, labor? • Placement • Methods • Delivery tickets • Pumping, pp. 280-81 • Construction joints 2005, Randy R. Rapp

  9. Weather Extremes • Heat > 90oF • Time of day • Crushed ice replaces water lb for lb • Enclosure? • Cold < 40oF • Heat components • Enclosure • Not only temperature, but also gradient from time rate of internal temperature change 2005, Randy R. Rapp

  10. Concrete Tests • Pass, substantially comply, or fail • Random, representative samples • Sample from middle 70% of batch • Waste tested concrete • Make sure number and type of tests are specified 2005, Randy R. Rapp

  11. Statistics in Quality Control • Specifications can use statistics to derive target values that should be achieved. • Tolerances can be based on variations in materials, testing, processes, and sampling. • They consider all variable factors that influence outcomes. • They can be realistic and enforceable. 2005, Randy R. Rapp

  12. Randomness of Testing • Obtained by purposeful action • Not haphazard selection • Not merely without intentional bias • Each part of a batch, each lot, should have same chance of being chosen as any other. 2005, Randy R. Rapp

  13. Randomness of Testing(Cont’d) • A lot is a prescribed and defined quantity of material from the same process, for the same purpose. • All sampling and testing requirements are in relation to the lot. • Must establish lot size to determine proper sampling location and frequency. • Sublots, e.g., for paving batches • keep sampling and testing spaced out more evenly • reduces chance of extended periods without testing, such as start and finish periods. 2005, Randy R. Rapp

  14. Three layers of equal volume, not height Measure to center of slumped sample, not highest point Changes in slump indicate changes in consistency: find out why Slump Test 2005, Randy R. Rapp

  15. Type A (shown) and Type B meters Consolidate to remove voids Air pressure collapses entrained air Volume change is correlated to bowl volume to find % air Air Entrainment Test 2005, Randy R. Rapp

  16. Yield Tests • Sample introduced into 0.5-ft3 (≤ 1.5-in aggregate) or 1-ft3 (≤ 3-in aggregate) mold • Three equal volume layers: rod 25 times in smaller mold, 50 in larger 2005, Randy R. Rapp

  17. Cylinders (6-in x 12-in) for compressive strength Beams (6-in x 6-in x 20-in) for flexural strength Larger molds if aggregate >2-in Two samples from middle of batch Cylinder and Beam Tests 2005, Randy R. Rapp

  18. Inspection During Placement (Cont’d) • Consolidation • Spading or rodding • Vibration • Finishing • Floating • Trowelling 2005, Randy R. Rapp

  19. Inspection After Placement • Checklist, Table 10-14 • Curing • Stripping and reshoring • Protection 2005, Randy R. Rapp

  20. Records and Reports • See pp. 300-301 2005, Randy R. Rapp

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