Water and Admixture

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CE 165: Concrete Materials and Concrete ConstructionCE 165: Concrete Materials and Concrete Construction

Water and AdmixturesWater and Admixtures


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WaterWatermunicipal water is fine for concrete.salt water can be used for plain concrete but

causes problems for reinforced andprestressed concrete.

mining water can cause problems due to the

presence of salts, acids, oil, sugar, andorganic matter. Take the unknown water andmake concrete cylinders and compare thetime of set and strength to the concrete

made with good water. The strengthdifference should be less than 10%.

almost any water is good for the curing of

concrete. Some may cause discoloration,though.


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ADMIXTURESADMIXTURES

Reasons

(1) Improve or modify some or several

properties of portland concrete.(2) Compensate for some deficiency


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AdmixturesAdmixtures

Classification (pages 257-258)Surfactants (0.05-0.5%; new ones

2%)Chemical Admixtures (1-4% by

weight of cement)

Mineral Admixtures (> 15% by

weight of cement)


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A short (but important

detour into surface chemistry)

A short (but important

detour into surface chemistry)

The presence of a surface breaksthe molecular symmetry that exists

inside a material.The molecules at the surface have

different energy than the

molecules inside the bulk material.


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Surface energySurface energySurface energy, Usurf, is the

difference between the energy ofthe molecules at the surface and

the energy that they would havewithin the body.

Usurf

Swhere S is the area of the interface and a is the surface tension.


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Nature brings a body to its minimum energy.

Small spherical drops of l iquid and gasbubbles are good examples of surfaceminimization for a given volume.

The decrease in surface induces acontraction of the drop, increasing itsinternal pressure and making it higherthan the external pressure.

A balance of energy requires that thereduction in surface energy (dS) be equalto the work done by the surface forces inreducing the surface.

The work done can be expressed as where isthe volume change.

dSpsurf d


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ApplicationsApplications

psurf 2 r

Cylinder of radius r and height hS 2 rh V r2

h

psurf r

as the size of the sphere or the cylinder decreases, themagnitude of the surface pressure increases greatly

S 4r2 V 4 r3 3Sphere of radius r,


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Consider a thin layer of liquid

between two parallel plates

Consider a thin layer of liquid

between two parallel plates

psurf

r

2 cos

d


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Remember sand castlesRemember sand castles

http://www.philipshelley.com/words/


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Mechanism of DetergentsMechanism of Detergents

soiled surface addition of water containing

a surfactant

detergent gets adsorbed in all surfaces during agitation

From Hunter, Introduction to Modern Colloid Science, (1995).


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Soap bubbleSoap bubbleA soap bubble

consists of a thinsphere of water in

contact with the polar

heads of soapmolecules on both

sides. From R.

Cotterill, TheCambridge Guide to

the Material World,

1989.


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A simple demonstrationA simple demonstration


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Nearly all glues are plastic polymers-giantmolecules that cling to themselves and the

surfaces they touch, like sauceless

spaghetti noodles left overnight in a bowl.

But while the plastic molecules in most

household glues are dissolved in a liquidthat evaporates as the glue dries, the

molecules in Krazy Glue--and other

instant glues--do not form until you squirt

the liquid out of the tube.

From A. Bloomfield , Am. Scien


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Cont.Cont.

Krazy Glue is remarkable because it isalmost pure ethyl-2-cyanoacrylate, asimple molecule that polymerizes rapidly

when exposed to moisture. Each gluemolecule contains an unusually fragiledouble bond between carbon atoms, one

that is easily attacked by the hydroxyl ionsfound in most airborne moisture.


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Surface - Active Chemicals

(Surfactants)

Surface - Active Chemicals

(Surfactants)

long-chain organic molecules, oneend of each is hydrophilic (water-

attracting) and the other

hydrophobic (water-repelling).

hydrophilic end contains one or

more polar groups, such as -COO--SO3-, or -NH3+.


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Air-Entraining SurfactantsAir-Entraining Surfactants

Salts of wood resins, protainaceousmaterials and petroleum acids, and

some synthetic detergents.


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Air-Entraining SurfactantsAir-Entraining Surfactants


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Advantages of Using Air-

Entrained Surfactants

Advantages of Using Air-


Freezing and thawing cyclesImprove workability

Reduce tendency for segregationand bleeding


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Ice Formation in ConcretIce Formation in Concret


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Air VoidsAir Voids


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Ice Forming in Air VoidsIce Forming in Air Voids


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Disadvantages of Using Air


Disadvantages of Using Air


Loss in strength ( for each 1% of aircauses 5% loss in strength)

Increase permeabilityIn case of overdoses, they cause

delay in setting and hardening


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Effect of air-entrainmentEffect of air-entrainment


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Water Reducing AgentsWater Reducing Agents

Salts and derivatives oflignosulfonic acids, hydroxylated

carnoxylic acids, and

polysaccharides.

The anionic polar group is joined to

hydrocarbon chain which itself ispolar or hydrophilic.


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Water Reducing AgentsWater Reducing AgentsSalts and derivatives of l ignosulfonic

acids, hydroxylated carnoxylicacids, and polysaccharides.

The anionic polar group is joined tohydrocarbon chain which itself is

polar or hydrophilic.


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ExamplesExamples


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MechanismMechanism

The polar chain is adsorbed alongside the cement

particle; instead of directing a nonpolar end toward

water, in this case the surfactant directs a polar end,lowering the surface tension of the water and making

the cement particle hydrophilic.


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ConsequenceConsequence

As a result of layers of water dipoles surrounding

the hydrophilic cement particles, their

flocculation is prevented and a well-dispersed

system is obtained.


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Advantages of Using Water-

Reducing Admixtures

Advantages of Using Water-

Reducing Admixtures

Increase the consistency

Achieve higher compressive strength

Cement saving

Important: not all three benefits canbe obtained at the same time


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Lignosulfonate as a Water

Reducer

Lignosulfonate as a Water

Reducer

O

H3CO

O

OH

H3CO

SO3Na

HO

n

Courtesy from Carmel JOLICOEUR


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SuperplasticizersSuperplasticizersConsist of sulfonated slats of melamine

or napthalene formaldehydecondensates.

Also called high range water-reducingadmixtures because they are able to

reduce 3 to 4 times water compared to

normal water-reducing admixtures.


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SuperplasticizersSuperplasticizersLong-chain, high-molecular mass

anionic surfactants with a largenumber of polar groups in the

hydrocarbon chain.

Normal dosage: 1-2% by weight of

cement.


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SuperplasticizersSuperplasticizers25 to 30% of water reduction for a given

consistency (normal plasticizer: 5 to10% of water reduction).

No problem with bleeding andsegregation because of the colloidal

size of the long-chain particles of the

admixture which obstructs the path of

the bleed water.


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flocculated deflocculated dispersed in less water

"Physical" effects operative in any slurry or paste

High

fluidity

Intermediate

fluidity

Low

fluidity

Mode of Action of Superplasticizers

"Physical" binding and dispersion


"Physical" binding and dispersionCourtesy from Carmel JOLICOEUR

Ill t ti f Ph i lIll t ti f Ph i l


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Illustration of Physical

Dispersion Effect

Illustration of Physical

Dispersion Effect

Mineral Paste+10 % water +0.1 wt% PNS



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M+n

HRWR or Superplasticizers:

Synthetic Water-Soluble Polyelectrolytes

HRWR or Superplasticizers:

Synthetic Water-Soluble Polyelectrolytes

Type of monomer

Length (Mw)

Branching, cross-

linking

Charge,

counter-ions

- - - - - -

Co-polymers

(building blocks)


Structure ofStructure of


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Structure of

PolyNaphthaleneSulfonate (PNS)

Structure of

PolyNaphthaleneSulfonate (PNS)

CH2

SO3Na

nCourtesy from Carmel JOLICOEUR

Structure of PolyMelamineSulfonateStructure of PolyMelamineSulfonate


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Structure of PolyMelamineSulfonate

(PMS)

Structure of PolyMelamineSulfonate

(PMS)

N N

N NHNH

HN

O

SO3Na

nCourtesy from Carmel JOLICOEUR


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Structure of a Co-PolymerStructure of a Co-Polymer

CH

C

CH CH2

COONa

NH

CH

N

SO3Na

n

O

O


St t f P l A li E tSt t f P l A li E t


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Structure of PolyAcrylic Esters

(PAE)

Structure of PolyAcrylic Esters

(PAE)

CH2 C

R1

COONa

CH2 C

R1

CO

On m

R

CH2 C

R1

X o


aracter zat on oaracter zat on o


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aracter zat on o

Superplasticizers

aracter zat on o

SuperplasticizersBulkpH, conductivity

% solidviscosityspecific gravitysurface tension

loss on ignition, TGA

Physico-chemicalelemental and ionic

analysisacid-base titrationcharge densitymolar mass distribution

NMR, IR, UV spectroscopy

Functional

rheology of pastes (inert

or reactive minerals)

zeta potential on

reference minerals (dilute)adsorption on various

minerals (dilute and

pastes)

influence on hydrationreactions

specific interactionsCourtesy from Carmel JOLICOEUR

Typical Scale of Components in

Typical Scale of Components in


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500X

SF

SF

50X

SO4

Typical Scale of Components inSF-Cement PasteTypical Scale of Components inSF-Cement Paste

SF

Cement

SF


Influence of PNS onInfluence of PNS on


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Influence of PNS on

Ettringite Morphology

Influence of PNS on

Ettringite Morphology

Without PNS With PNS


M d f A ti f S l ti iM d f A ti f S l ti i


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"Chemical" Effects: Changes in morphology


"Chemical" Effects: Changes in morphology

SEM micrographs of a high alkali

cement paste

0% PNS; 30 min hydr. 4% PNS; 30 min hydr.


OPTIONS IN SP APPLICATIONSOPTIONS IN SP APPLICATIONS


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OPTIONS IN SP APPLICATIONSOPTIONS IN SP APPLICATIONS

30

40

50

60

120 140 160 180 200 220 240

Water content (kg/m

3

)

Flowtab

lespread(cm)

with SP

without SPIncreased

strength

Increasedworkability



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New Generation of

Superplasticizers

New Generation of

Superplasticizers


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MechanismMechanism


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Mechanism 2Mechanism 2


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Mechanism 4Mechanism 4

ASTM Categories (C494) :ASTM Categories (C494) :


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ASTM Categories (C494) :

Water Reducers

ASTM Categories (C494) :

Water Reducers

Low range: water reduction of 5% (minimum)

WR (e.g. lignosulfonate)

Type A : normal

Type D : WR and retarding

Type E : WR and accelerating

High range: water reduction of 12% (minimum)

HRWR, Superplasticizer (synthetic polymers:naphthalene-, melamine- or acrylate- based)

Type F : normal

Type G : HRWR and retarding


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Set-Controlling ChemicalsSet-Controlling Chemicals

Rheological changes in a freshconcrete mixture

Stiffening: loss of consistency by theplastic cement paste


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Set-Controlling ChemicalsSet-Controlling Chemicals

Setting: beginning of solidification. Atthe initial set the paste becomes

unworkable so the placement,

compaction and finishing of concretebeyond this point becomes difficult (4

to 6 hrs. at 70 F). Final set is the time

required for the paste to solidifycompletely.

Hardening: strength gain with time.


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ClassificationClassification

Accelerator: decreases the settingtime.

Retarder: increases the setting time.


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Mechanism of Action (I)Mechanism of Action (I)

The action of set-controlling chemicalson portland cement can be attributedmainly to dissolving of the anhydrousconstituents forming anions (silicateand aluminate) and cations (calcium),the solubility of each being dependenton the type and concentration of the

acid and base ions present in thesolution.


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Mechanism of Action (II)Mechanism of Action (II)

An accelerating admixture mustpromote the dissolution of the

cations (calcium ions) and anions

from the cement.

A retarding admixture must impede

the dissolution of the cementcations (calcium ions) and anions.


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Mechanism of Action (III)Mechanism of Action (III)

The presence of monovalent cations insolution (i.e., K+ or Na+) reduces the

solubility of Ca2+ ions but tends to

promote the solubility of sil icate andaluminate ions. In small

concentrations, the former effect is

dominant; in large concentrations, thelatter effect becomes dominant.


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Mechanism of Action (IV)Mechanism of Action (IV)

The presence of certain monovalentanions in solution (i.e., Cl, N03-, or

S042-) reduces the solubility of

silicates and aluminates but tends topromote the solubility of calcium ions.

In small concentrations, the former

effect is dominant; in largeconcentrations, the latter effect

becomes dominant.


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Accelerating admixturesAccelerating admixturesUseful for modifying the properties of concrete,

particularly in cold weather, to:(a) expedite the start of finishing operations and, when

necessary, the application of insulation forprotection;

(b) reduce the time required for proper curing andprotection;

(c) increase the rate of early strength development soas to permit earlier removal of forms and earlieropening of the construction for service; and

(d) permit more efficient plugging of leaks againsthydraulic pressures.


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Accelerating admixturesAccelerating admixtures

Calcium chloride is by far the bestknown and most widely used

accelerator. See Table 8.3 for the

potential problems in using suchadmixture.

There are accelerators that do notcontain choride: calcium formate,

formic acid.


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Retarding admixturesRetarding admixtures

Compensation for adverse ambienttemperature conditions particularly

in hot weather. Extensive use is

made of retarding admixtures topermit proper placement and

finishing and to overcomedamaging and accelerating effects

of high temperatures.


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Chemical AdmixturesChemical Admixtures


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Type A: water-reducing

Type B: retarding

Type C: acceleratingType D: water-reducing and retarding

Type E: water-reducing and accelerating

Type F: high-range water-reducing

Type G: high-range and retarding


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Case StudyCase StudyHighly Variable Air Content

On a recent job we found large

variations in the air content of our

concretes. The mixture contained 500

lb of cement per cubic yard and wasmade with a 1 in. aggregate. The air

content had to be between 5% and 7%,

but in certain cases the air content wasconsiderably higher or very low. What

could be causing this phenomenon?


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SolutionSolutionThe air content of concrete can vary for any of a

number of reasons. Increasing fineness of the sandcan reduce the air content; the presence of organicmatter in the sand, which can act as an air entrainingagent can increase air content. By mixing dyes ororganic materials into the concrete, one can lower

the concrete's air content.An overdose of admixture or a reduction of cementcan increase air content. Changing the brand ortype of cement, or the kind of supplementary

cementitious material used, can raise or lower theamount of air. Calcium chloride increases aircontent in mixes rich in cement, but not so in leanmixes.


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Case StudyCase StudyToo Much Air

For many years, we've notice that our concrete has atendency to contain too much air, a phenomenonwhich has recently become worse We have tried,without success, reducing the amount of airentraining agent, we've even changed the supplierwithout any success.We've always used aggregates which come from aquarry and a sand pit near our site (3 to 4 milesaway). Given that we are in a fairly remote region, it

is economically impossible for us to changesuppliers (the next closest sand pit is 50 m away,while the next closest quarry is 60 miles away).What should we do?

Water and Admixture

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