CIE 111: Civil Engineering Materials Laboratory


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concrete memo series step 4 of  4 - the END.

Overview

Time to break the concrete!  The cylinders are tested in compression to failure.  A strainometer is used on one cylinder to record compressive displacements.  A non - destructive Schmidt hammer test is also performed for comparison.

The reinforced beam is also broken as a demonstration.

Concrete Cylinder test

Broken Concrete Beam

Concrete Cyclinder test

Concrete strength

Concrete Cylinder Strengths at 7 and 28 days -- See page 119 of the CIE 110 course notes for a more accurate representation.


Safety Info

Safety!
  • Safety glasses are required at all times while equipment is turned on.   Not only are safety glasses a good precaution, they prepare students for industry where they are also required.
  • Use containment cages around cylinders to prevent flying pieces upon failure
  • Long hair must be tied back so it doesn’t get caught in moving equipment.   Avoid wearing jewelry that may also become tangled in equipment.
  • The Schmidt hammer uses a large amount of force to test the hardness of a material. Do not put the Schmidt hammer up to your head!

Equipment Used

 

Procedures:

All data sheets [ xls ]

Capping Cylinders

  1. Remove the cylinders from the wet room.
  2. Place one neoprene cap on the top of the cylinder.
  3. Invert the cylinder and repeat the procedure for the other end.

Schmidt Hammering a Cylinder

The non-destructive Schmidt Hammer test will be performed on one cylinder for comparison.

  1. Place the cylinder in the compression machine.
  2. Apply a 2000 lb. holding load.
  3. Choose 12 relatively smooth locations at least one inch apart and evenly distributed around the side of the cylinder.
  4. With the plunger of the Schmidt hammer extended, slowly press the hammer against the side of the cylinder until the hammer is released and impacts against the cylinder. At the moment of impact, the hammer must be held perpendicular to the surface.
  5. Press the locking button on the side of the hammer to hold the reading. DO NOT PUSH THE LOCKING BUTTON BEFORE THE HAMMER HITS THE CYLINDER.
  6. Record the rebound number.
  7. After taking all 12 readings, compute a preliminary average rebound number.
  8. Disregard any tests with a rebound number that deviates from the preliminary mean by more than +/- 5 and compute the final mean rebound number.
  9. Use the correlation table provided to obtain the compressive strength from the final mean rebound number. Note the angle on the chart.

Testing a cylinder with strain readings

Measure strain on one cylinder

  1. Measure the diameter.
  2. Attach the strainometer to one cylinder.
  3. Measure the gage length with dial calipers.
  4. Record the deformation from the strainometer at 5000 pound load increments. The deformation measured by the dial gage is twice the deformation between the points where the apparatus is attached to the cylinder. Thus, divide the dial gage reading by two to obtain the deformation between the attachment points.

Testing a cylinder without strain readings

  1. Measure the diameter.
  2. Use a loading rate of 30 psi/second.
  3. Test to failure and record the failure load.

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Calculations  

  1. For all cylinders record the failure load, age of cylinder, and any unusual circumstances.
  2. For all cylinders compute the compressive strength using
    f'c = load/area.
  3. Compute the Schmidt Hammer results.
  4. Plot a stress-strain curve for the cylinder that was tested with the strainometer.   Include it in the results section of your report.
  5. Determine the secant modulus of elasticity from the stress-strain curve. The secant modulus of elasticity (E) is given by:
    E = (s 2 - s 1)/(e 2 – 0.000050)

    Where:
    E = secant modulus of elasticity in psi
    s 2 = stress at 40% of ultimate load
    s 1 = stress at strain of 0.000050
    e 2 = strain at 40% of ultimate load

 


 


McCormick, Amber and Manion, William. "University of Maine Civil Engineering Materials Course Manual CIE 111." 03 September, 2013.  http://www.civil.umaine.edu/cie111/.
 
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