3 point bending experiments

Poor compressive strength means that reinforcement phase is needed. here are different ways to reinforce the mix.

  • Internal – using metal mesh,rebar or glass fibre
  • Add cement to the mix
  • Change manufacturing method
  • Prestressed specimens

In order to choose the best reinforcement way, I had to set the evaluation factors:

  • Strength, stiffness, brittle or ductile, yield displacement
  • Consistency of results
  • Addition in weight and cost

R01    Normal process-Pressed specimens
R02    Normal process- 2x cement amount
R03    Normal process-Normal mix
R04    Normal process-Add glass fibres
R05    Normal process-Add chicken wire
R06    Different paper quality
R07    New process-Normal mix
R08    New process- Chicken wire
R09    New process- Add glass fibres

During the drying period, I examined the specimens weekly to get information about its physical properties.

Density loss in different reinforced specimens

  • Increasing the cement  (double) in the mix adds 50% in weight
  • Highest density – Pressed specimens, Lowest density – Normal mix

After specimens were dry, they were moved in the Lab to be tested for 3 point bending machine.

3 point bending test. Crack is visible

Bending test, all specimens

Simple mix - no reinforcement

  • Poor properties, brittle, yield displacement≈4mm
  • Consistent results
  • Linear behavior

Add cement in the mix

  • Average flexural strength σfM  increase 3 times, brittle, yield displacement≈7mm
  • Less consistent results
  • Less linear elastic behavior

Pressed specimes

  • Flexural strength small  increase, brittle, yield displacement≈2mm
  • Large deviations in values. Further research on the process
  • Linear behavior

Glass fibers

  • Flexural strength 2 times higher, brittle, yield displacement≈5mm
  • Deviations in values. Difficult to standardize the quantity, position and direction of fibres
  • Linear behavior

Metal wire

  • Higher average flexural strength σfM that glass fibers, ductile,
  • Consistent results
  • Noninear behavior. Difficult to model materials behavior

I must evaluate the different reinforcement ways, and find which will work better in my design process.


About Menelaos Kokkinos

Menelaos Kokkinos TU Delft mgkokkinos@gmail.com
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