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 FumeSilica FumeSilica FumeSilica 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 POLYPROPYLENE POLYPROPYLENE POLYPROPYLENE

FIBERSFIBERSFIBERSFIBERS

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 fibers 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/cips/35p.pdf

SUPERIOR SUPPLIES INC.SUPERIOR SUPPLIES INC.SUPERIOR SUPPLIES INC.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!