Concrete

haplessuseUrban and Civil

Nov 25, 2013 (3 years and 6 months ago)

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Concrete

Admixtures



Team Members:



Navid Borjian

Dean Arthur

Rey Alcones

Angelique Fabbiani
-
Leon


SRJC Engr. 45

December 7, 2009

Concrete

is composed mainly of cement (commonly Portland cement),
aggregate, water, and chemical admixtures.


Portland Cement

Fine Aggregate

Coarse Aggregate

Chemical Admixtures


Concrete solidifies and hardens after mixing with water and placement due
to a chemical process known as hydration.


The water reacts with the cement, which bonds the other components
together, eventually creating a stone
-
like material.



Concrete is used more than any other man
-
made material in the world.


The word concrete comes from the Latin word "concretus" (meaning
compact or condensed).


The first major concrete users were the Egyptians in around 2,500 BC and
the Romans from 300 BC.


Opus caementicium laying bare on a tomb near Rome. In
contrast to modern concrete structures, the concrete
walls of Roman buildings were covered, usually with
brick or stone.

Outer view of the Roman Pantheon, still the largest
unreinforced solid concrete dome to this day.


Concrete has many applications and is used to make pavements, pipe,
structures, foundations, roads, bridges/overpasses, walls and footings for
gates.


Properties:


Concrete has relatively high compressive strength, but significantly lower
tensile strength, and as such is usually reinforced with materials that are
strong in tension (often steel).



The elasticity of concrete is relatively constant at low stress levels but starts
decreasing at higher stress levels as matrix cracking develops.



Concrete has a very low coefficient of thermal expansion, and as it matures
concrete shrinks.



All concrete structures will crack to some extent, due to shrinkage and
tension.



Concrete can be damaged by fire, aggregate expansion, sea water effects,
bacterial corrosion, leaching, physical damage and chemical damage (from
carbonation, chlorides, sulfates and distillate water).

Types of Concrete:


There are various types of concrete for different applications that are created by changing the proportions of the
main ingredients.



The mix design depends on the type of structure being built, how the concrete will be mixed and delivered, and how
it will be placed to form the structure.



Examples include:



Regular concrete


Pre
-
Mixed concrete


High
-
strength concrete


Stamped concrete


High
-
Performance concrete


UHPC (Ultra
-
High Performance Concrete)


Self
-
consolidating concretes


Vacuum concretes


Shotcrete


Cellular concrete


Roller
-
compacted concrete


Glass concrete


Asphalt concrete


Rapid strength concrete


Rubberized concrete


Polymer concrete


Geopolymer or Green concrete


Limecrete


Gypsum concrete


Light
-
Transmitting Concrete

Regular Concrete


Cement, Aggregate, and water


Geopolymer (
Green

concrete)

Fly Ash and Regular

Concrete


High Strength Concrete

~<0.35%

Silica Fume

Strong Aggregates


Ultra High Performance Concrete (UHPC)


Cement

Coarse/Fine Aggregate

Air

Silica Fume

Polypropylene Fibers

Basic Composition for Main Concretes


Our Samples:


Sample 1:



Portland cement + coarse aggregate + fine aggregate + water



Sample 2:



Portland cement + coarse aggregate + fine aggregate + water +


fly ash + water reducer



Sample 3:



Portland cement + coarse aggregate + fine aggregate + water +


fly ash + water reducer + silica fume



Sample 4:



Portland cement + coarse aggregate + fine aggregate + water +


fly ash + water reducer + silica fume + polypropylene fibers




Admixtures and Properties

Background


There are two types of fly ash used
in concrete which is classified as
Class
-
C and Class
-
F.


Class
-
F is more widely used
because it is made from the burning
of older anthracite (i.e. black coal ,
black diamond, etc.) which is in
abundance, with an opposing
amount of uses.



Fly ash that is not used in concrete
is poured in landfills with it’s micro
dust particles to flutter in the
atmosphere.


As far as human health is concern,
fly ash in itself contains traces of
heavy metals which pertains to
arsenic, selenium, lead, and more.

Benefits


For every ton of Portland cement one ton of carbon dioxide is released into the atmosphere. Decreasing the
amount of Portland cement would lower the carbon emissions. Replacing this portion with fly ash would help with
decreasing the amount of Portland cement needed as well as making use for the ash that would otherwise be put
in landfills or the factories.



Decreasing the amount of water is always a benefit when it comes to cement. Fly ash lowers the amount of
water needed because it’s smoother and spherical shape on a micro level allows the concrete to have more
consistency without plasticizing with more water.


Fly ash lowers the amount of voids (compared to regular cement) because of the particles’ small size.


Fly Ash

Background


Being a pozzolan, fly ash has the
ability to act cementitious with the
presence of cement and water. This
process is able to happen because
of fly having silica and alumina.



Fly ash on a micro level takes the
form of a sphere which allows the
particle to fit easily within the pores
of the concrete. This circular form of
the fly ash also allows the concrete
to be more fluid and workable. When
it comes to setting the concrete, it’s
a benefit for workers by it having
this feature making it easier to place.


Silica Fume

Properties



When silica is in combination of alkali
which is found in the concentration of
concrete a destructive reaction occurs.
When alkali is in the presence of silica
hydroxyl ions expansion occurs causeing
crakes, which is why a low
-
alkali cement
is used in the presence of silica fume.


Silica fume, like fly ash, is a pozzolan
and has cement properties. Silica fume
as the ability to act as if it were cement
(with the presence of water and cement
of course) because its’ extremely small
particles (at the size of about 1/100th to a
cement particle) , having a considerable
amount of silicon dioxide, and large
surface area makes the admixture an
active pozzolan.


When concrete has silica fume and low
water the outcome of the concrete
becomes highly resistant which causes
penetration by chloride ions.


Benefits



When concrete has silica fume the strength is greatly increased,
having an average compressive strength of 15,000psi.



With silica fume being very resistant to corrosion, concrete with
silica fume is now being used in bridges and for rebuilding older
structures.


Silica fume molecules have the ability to combine with calcium
hydroxide (which is exhaled from the cement during the
hydration process) which increases the cement’s overall
durability.


Since silica fume’s particle is extremely small which makes it
able to fit into the voids made from the spacing between the
cements’ particle, it reduces permeability. Being a microfiller
helps protect the reinforcing steel from the concrete.

Polypropylene
Fibers

Benefits


With the addition of polypropylene fiber in the mixture of concrete it enhances the toughness and tensile strength. When
concrete is by itself it has the tendency to be very brittle especially in the area of a tensile test which is where the fibe
rs
come into play to build in where regular concrete lags, which can increase the compressive strength to a dramatic level.




In coastal areas there is a high concentration of chloride ions from the salty air, this creates corrosion with the steel
product which produces rust as a result. This rust has the capacity to expand four to ten times larger than the iron causing
a large expansion which makes crakes and voids. Polypropylene fibers now are underway in replacing the reinforcing
steel in concrete, which has a much greater strength and can reach up to 20k psi.

Background


Polypropylene is a recent additive to cement as of the 1960s,
whereas other fibers are underway of being tested strength
wise for concrete.

Properties


When regular concrete is under a great amount of compression it will spilt and deform on the spot into separate
pieces once it reaches its greatest tensile load. Mixing

sporadically polypropylene fibers into the cement will
balance this effect by attaching to the other piece that wants to spilt away and maintain both sides for a longer
duration.

Making Our

Samples






Slump Test


The goal of the test is to measure the
consistency of concrete through out the mix.



"Slump" is simply a term coined to describe how
consistent a concrete sample is.



The test also further determines the workability
of concrete, how easy is it to handle, compact,
and cure concrete.



By adjusting the cement
-
water ratio or adding
plasticizers to increase the slump of the concrete
will give a desired mix.


Process


Fill one
-
third of the cone with the concrete mixture. Then
tamp the layer 25 times using the steel rod in a circular
motion, making sure not to stir.



Add more concrete mixture to the two
-
thirds mark. Repeat
tamping for 25 times again. Tamp just barely into the
previous layer(1")



Fill up the whole cone up to the top with some excess
concrete coming out of top, then repeat tamping 25 times.
(If there is not enough concrete from tamping compression,
stop tamping, add more, then continue tamping at previous
number)



Remove excess concrete from the opening of the slump
cone by using tamping rod in a rolling motion until flat.





Slowly and carefully remove the cone by
lifting it vertically (5 seconds +/
-

2
seconds), making sure that the concrete
sample does not move.




After the concrete stabilizes, measure the
slump
-
height by turning the slump cone
upside down next to the sample, placing
the tamping rod on the slump cone and
measuring the distance from the rod to the
original displaced center
.





A change in slump height would
demonstrate an undesired change in the
ratio of the concrete ingredients; the
proportions of the ingredients are then
adjusted to keep a concrete batch
consistent. This homogeneity improves the
quality and structural integrity of the cured
concrete.





Data & Results

What We Learned

Our Procedures


Test first sample at 11 days, second sample at 18 days.



Test third sample (comprised of two cylinders) at 25 days.



First two samples and one of the third samples loaded wet
side down.



Last sample loaded dry side down.



Photograph and record ultimate failure loads.

Common Failure Modes

Our Failure Modes

Test 1

Load:28000#

Psi:990

Load:32000#

Psi:1132

Load:38500#

Psi:1362

Load:33000#

Psi:1167

Sample 2

Sample 1

Sample 3

Sample 4

Our Failure Modes

Test 2

Load:46000#

Psi:1626

Load:25500#

Psi:902

Load:20000#

Psi:707

Load:62500#

Psi:2210


Sample 1

Sample 2

Sample 3

Sample 4

Our Failure Modes

Test 3

(Two Cylinders)





(Averaged)
Load: 33750#

Psi:1194


(Averaged)

Load:28250#

Psi:999

(Averaged)

Load:39500#

Psi:1397

(Averaged)

Load:41500#

Psi:1468

Sample 1

Sample 2

Sample 3


Sample 4

Results from Data

15
20
25
30
35
40
45
50
55
60
65
9
11
13
15
17
19
21
23
25
27
Pressure (Kilo
-
Pounds)

Cure Time (Days)

Concrete
Age/Admixture Strengthening

Sample 1
Sample 2
Sample 3
Sample 4
Interpretation of Data


General trend of all samples (except sample 2) were
upward.



Silica Fume and Silica Fume/Fiber mix did appear to
increase overall compressive strength.



Fly Ash data may be inconclusive when considering other
sample’s upward trends.



Appears that all samples may have been affected more by
the constant water ratio (.45) than admixtures.


Potential Sources of Error

(Based on Standardized Testing Methods)



“A test result is the average of at least two standard
-
cured strength specimens made from the same
concrete sample and tested at the same age. In most
cases strength requirements for concrete are at an
age of 28 days”



“To provide for a uniform load distribution when
testing, cylinders are capped generally with sulfur
mortar”



“The loading rate on a hydraulic machine should be
maintained in a range of 20 to 50 psi/s”


Conclusion


Failure mode observed was non standard, but appears
potentially related to machined grooves in testing
apparatus.



Lack of over
-
all data points makes first two tests
relatively inconclusive.



Concrete never reached potential compressive
strength (even with anomalous samples).



Water Ratios appear to affect compressive strength
more than admixtures.

References


Images:


http://img.ecplaza.com/my/metfabExportHouse/7.jpg


http://www.fhwa.dot.gov/pavement/pccp/pubs/04150/images/fig138.gif


http://www.buildinggreentv.com/files/u5/concrete.jpg


http://www.luxuryhousingtrends.com/artistic
-
concrete
-
flooring.jpg


http://www.engineeringfiber.com/images/products/polypropylene_fiber.jpg



Text:


http://en.wikipedia.org/wiki/Anthracite


http://www.toolbase.org/Technology
-
Inventory/Foundations/fly
-
ash
-
concrete


http://www.nytimes.com/2008/12/25/us/25sludge.html


http://www.silicafume.org/general
-
silicafume.html


http://www.concretenetwork.com/concrete/concrete_admixtures/silica_fume.htm


http://www.uritc.uri.edu/media/finalreportspdf/536101.pdf


www.nrmca.com/aboutconcrete/
cip
s/35p.pdf








Superior Supplies Inc.

40 Ridgway Ave

Santa Rosa, CA 95401

(707) 546
-
7864


Very

special thanks to
Burt Lockwood

and everyone
at Superior Supplies Inc.! As a group we cannot
express enough how much we appreciate the help,
materials, time and knowledge given to us for this
concrete compression project!