Mechanical Testing of Concrete Flashcards
What are the specifications for testing in compression?
-Cubes (100-300 mm) or cylinders (100-300 mm diameter, with aspect ratio 2.0)
-Loaded faces must be flat
-Smaller specimens are stronger, because failure occurs at largest flaw
-Cylinders fail at lower loads due to the less restraint on faces
What is an extrinsic property of concrete?
Strength (depends on sample size)
What are the intrinsic properties of concrete?
Density, melting point, temperature
Why are specimens not often tested in tension?
Tension tests are sensitive to specimen geometry, size and loading rate
What is creep testing?
Stressing a material at a load well below failure for a long time
What causes concrete creep?
C-S-H nanogranules in the microstructure sliding over each other and becoming compressed/deformed under load
How should a creep tests samples be arranged?
-Test the samples for around 12 months
-Load samples at different ages (2-90d) to get better understanding of effects of binder maturity
How does creep levels effect cracking?
Low tensile strength and low creep will crack more
What is electrochemical testing used for?
To check the condition of reinforcing steel (detect corrosion currents)
What are radiographic or radar-based methods used to determine?
To identify the location of reinforcement, the condition of the cover concrete, or large cracks
What is the Schmidt (rebound) hammer test?
To see how much the hammer bounces off the surface
What is the Windsor (penetration) prove used for?
To see how far into the surface can a projectile penetrate
What is the pullout test used for?
A bolt is screwed into a drilled hole, and the difficulty to pull it out is measured
What is the ultrasonic pulse velocity test used for?
To see how well the microstructure of the material transmits ultrasound
