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ACI. Concrete Field Sampling. AASHTO Concrete Classifications. Concrete for use in highway bridges is defined as Class A, B, C, P, or S. Class A is prescribed unless another class of concrete is more appropriate. Class A concrete shall contain six (6) sacks of cement to the cubic yard

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Concrete Field Sampling

aashto concrete classifications
AASHTO Concrete Classifications
  • Concrete for use in highway bridges is defined as Class A, B, C, P, or S.
  • Class A is prescribed unless another class of concrete is more appropriate.
    • Class A concrete shall contain six (6) sacks of cement to the cubic yard
    • The water content shall not exceed six (6.0) U.S. gallons

per sack of cement (W/C < .54)

  • Class B concrete is for footings, pedestals, massive pier shafts, and gravity walls.
    • Class B concrete shall contain five (5) sacks of cement to the cubic yard.
    • The water content shall not exceed six and a half (6.5) gallons per sack of cement (W/C < .58
  • Class C concrete is prescribed for thin sections
  • Class P concrete is used when compressive strengths in excess of 4,000 psi
  • Class S is used for concrete deposited underwater
frequency of field sampling
Frequency of Field Sampling
  • ACI defines requirements of evaluation and acceptance of concrete on the job.
  • 3 criteria establish the required minimum sampling frequency:
    • Once each day a given class is placed, nor less than…
    • Once for each 150 yd3 of each class placed each day, nor less than….
    • Once for each 5000 ft2 of slab or wall surface area placed each day
  • Minimum of 5 tests are required if less than 5 batches are required.

Frequency of Field Sampling

  • When less than 50 yd3 of concrete are to be placed:
    • strength tests not required if satisfactory evidence of strength has been submitted and approved (previous quality assurance discussion)
field sampling testing
Field Sampling & Testing
  • A standard cylinder mold is 6” in diameter and 12” high.
  • One test result is considered the average of two cylinders at 28-days.
  • Not more than one test (2 cylinders) shall be taken from a single batch.
  • Water may not be added to the batch after the sample is taken.
sampling the concrete
Sampling The Concrete
  • Proper molding of cylinders for compressive strength:
    • Molded on rigid surface free of vibration
    • Placed in 3 lifts
    • Rodded 25 strokes per layer
    • To consolidate the layers, tap the outside of the cylinder lightly with the rod until holes close
    • Trowel finish the top surface
    • Cover with a plastic lid once bleed water has evaporated
sampling the concrete7
Sampling The Concrete
  • Flexural Beams:
    • Modulus of Rupture for Pavement Design Purposes
    • 6” x 6” x 20” beams
    • Cast in two layers
    • Rodded once for each 2 in2 of surface area
    • Tapped with rubber mallet 10 times each layer
    • Spade along edges
    • Finish & cover
  • R=Pl
  • bd2
storing field samples
Storing Field Samples
  • Once field samples are taken:
    • Prevent:
      • evaporation
      • exposure to direct sunlight
      • Exposure to radiant heat sources
lab curing testing
Lab Curing & Testing
  • Once the samples arrive at the lab:
    • Demold
    • Store in moist condition
      • (limetank or moist-cure room)
    • Store at 73.4o +/-3o
    • Tested at 28-days
investigation of low strength test results
Investigation of Low-Strength Test Results
  • If lab-cured cylinders from the field have average strengths below specified by more than 500 psi:
    • Verify sampling & testing procedures:
      • Properly surfaced specimens?
      • Initial curing over 80° (in field)?
      • Frozen cylinders?
      • Extra days in the field?
      • Impact during transport?
      • Delay in curing at the lab?
      • Improper testing procedure?
    • Lab is held accountable
low results what then
Low Results: What Then?
  • 3 cores should be taken from the structure in question for each substandard lab test.
  • core tests shall be considered adequate if the average is equal to 85% of specified….and...
  • and if no single test is less than 75% of specified
when results are not acceptable
When Results are NOT Acceptable
  • Strengthening of the structure or removal / replacement is required!!
  • $$$$$$$$$$$$$$$$$$$$$$$$$$$$$