1 Lecture #19 Failure & Fracture. 2 Strength Theories Failure Theories Fracture Mechanics.
Fracture Strength of Concrete
Transcript of Fracture Strength of Concrete
Fracture Strength of Concrete
SRJC Engr 45
Max Ulloa Michael Perry Sol Gonzalez
To put the strength of concrete to the test
by reinforcing concrete blocks with steel
bars in a variation of positions and test
their bend strength.
Concrete is a building material made from the
combination of aggregate and cement binder.
The most common form of concrete is Portland
cement concrete, which consists of mineral
aggregate (generally gravel and sand), Portland
cement and water.
4000 BC
The Assyrians were the first to come up with the
modern use of concrete used today, using clay as
cement.
3000 BC
• Egyptians used mud mixed with straw to bind
dried bricks.
• Used lime and gypsum mortar as a binding agent
for building the Pyramids.
300 BC Romans used slaked lime, a volcanic ash called
pozzuolana.
Mixture was 1 part lime to 4 parts sand.
Animal fat, milk, and blood were used as
admixtures
Concrete does not solidify because water evaporates, but rather cement hydrates, gluing the other components together and eventually creating a stone-like material.
Composite
When set, has high compressive strength, low tensile strength
Brittle
Withstands high temperatures
Behaves as a ceramic
Pavements
Building structures
Foundations
Motorways/roads
Overpasses
Dams
Cracks are the most common causes of complaints in the concrete industry.
Cracks result from a wide range of factors. Including :
Thermal contraction
Drying shrinkage
Restraint to shortening
Applied loads
ΔL= αLoΔT
Concrete has a thermal expansion/contraction coefficient (α) of 5.5E-6 per °F. Which means…
If concrete is placed during a hot midday, a 40 degree drop in temperature during night would cause a .03 inch crack in a 10 ft length of concrete.
BUT….. They can be significantly reduced.
And this is where reinforcements come in! Horizontal reinforcement steel can be installed to reduce the number of cracks or prevent those that do occur from opening too wide.
o The degree of workability required
depends on three factors.
o These are the size of the section to be
concreted,
o The amount of reinforcement,
o Method of compaction to be used.
Sample:
Block zero is just concrete with no rebar.
1 2 3 4
Rebar Dimensions:
½” Diameter
For sample 1 and 2 : 8.25” long
For sample 3 and 4 : 8.75” long
Block Dimensions:
Width: 4” wide
Length: 8.5” long
Height: 2.5” tall
0 1
2
3
4
4
0
500
1000
1500
2000
2500
3000
3500
4000
4500
Block 0 Block 1 Block 2 Block 3 Block 4
Compression Results in Psi
The cement block with the two
diagonally-placed rebars yielded the
highest flexural strength of (3235.29 PSI).
Having a rebar in a linear plane
decreases the fracture strength while
having a two rebar in different directions
increase the fracture strength.
Shetty M S., Concrete Technology- Theory and Practice, S.
Chand Publishers, New Delhi, 2009.
http://www.roymech.co.uk/Related/Construction/Concrete_
beams_theory.html
http://inventors.about.com/library/inventors/blconcrete.htm
http://www.auburn.edu/academic/architecture/bsc/classe
s/bsc314/timeline/timeline.htm
https://www.santarosa.edu/about_srjc/campuses_centers/c
ampus_buildings/images/DonZumwaltParking.jpg