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Portland Cement Concrete Module #10 Prepared by Dr. Randy R. Rapp July 2005.

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Presentation on theme: "Portland Cement Concrete Module #10 Prepared by Dr. Randy R. Rapp July 2005."— Presentation transcript:

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

2 2005, Randy R. Rapp2 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

3 2005, Randy R. Rapp3 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

4 2005, Randy R. Rapp4 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/in 2 (psi) Slump –Indicates (does not measure) consistency –Match to formwork and reinforcement configuration –Determined mainly by amount of water per yd 3 –Δ1 gal/yd 3 concrete = Δ1-in slump

5 2005, Randy R. Rapp5 Steel Reinforcement Types –Bars –Welded wire fabric (WWF) Accessories –Bolsters and chairs –Ties and clips

6 2005, Randy R. Rapp6 Inspection Before Placement Plant –Consistency –Mix materials: tests, p. 264 –Batching and mixing equipment –Pre-stressed members –Reports, p. 268

7 2005, Randy R. Rapp7 Inspection Before Placement (Contd) 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

8 2005, Randy R. Rapp8 Inspection During Placement Checklist, Table 10-12 Delivery: adequate trucks, tools, labor? Placement –Methods –Delivery tickets Pumping, pp. 280-81 Construction joints

9 2005, Randy R. Rapp9 Weather Extremes Heat > 90 o F –Time of day –Crushed ice replaces water lb for lb –Enclosure? Cold < 40 o F –Heat components –Enclosure Not only temperature, but also gradient from time rate of internal temperature change

10 2005, Randy R. Rapp10 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

11 2005, Randy R. Rapp11 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.

12 2005, Randy R. Rapp12 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.

13 2005, Randy R. Rapp13 Randomness of Testing (Contd) 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.

14 2005, Randy R. Rapp14 Slump Test 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

15 2005, Randy R. Rapp15 Air Entrainment Test 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

16 2005, Randy R. Rapp16 Yield Tests Sample introduced into 0.5-ft 3 ( 1.5-in aggregate) or 1-ft 3 ( 3-in aggregate) mold Three equal volume layers: rod 25 times in smaller mold, 50 in larger

17 2005, Randy R. Rapp17 Cylinder and Beam Tests 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

18 2005, Randy R. Rapp18 Inspection During Placement (Contd) Consolidation –Spading or rodding –Vibration Finishing –Floating –Trowelling

19 2005, Randy R. Rapp19 Inspection After Placement Checklist, Table 10-14 Curing Stripping and reshoring Protection

20 2005, Randy R. Rapp20 Records and Reports See pp. 300-301

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