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