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Compatibility Issues in

Concrete Chemical Admixtures

CANMET/ACI INTERNATIONAL CONFERENCE ON

ADVANCES IN CONCRETE TECHNOLOGY IN THE MIDDLE EAST

Dubai, November 19-20, 2008

Carmel JolicoeurDepartment of Chemistry

Université de Sherbrooke

Sherbrooke, Qc, Canada

J1K 2R1

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Scope of Presentation

• Defining incompatibility: type and origin

• Chemical admixtures:

– Types

– Function

– Mode of action

• Interactions between admixtures

• Cement-admixture interactions

• Avoiding incompatibilities

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Compatibility / Incompatibility

• Compatibility: Every admixture in a cementitious mix

performs its expected specific role.

• Incompatibility: When the cementitious mix does not

behave as expected, for whatever reason,…… the

admixtures are incompatible.

– Detrimental: One or more admixture does not perform adequately

or predictably.

– Synergistic: When several admixtures are used simultaneously,

some of the admixtures perform better than when used individually.

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Compatible vs Incompatible

• Hardened concrete results from Reactions and

Interactions between Water and cement components:

C3S, C2S, C3A, C4AF, CaSO4, Alkali Sulfates, Silica

Fume, Fly Ash, CSH, Ettringite, AFm, etc.

• In the presence of chemical admixtures the evolution of

the Reactions / Interactions may be influenced

predictably (Compatible) or unpredictably (Incompatible)

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5

Origin of Incompatibilities ?

DIRECT INTERACTIONS

• Cement-Admixture interaction

• Admixture-Admixture interaction

INDIRECT INTERACTIONS

• Interactions involving 2 or more admixtures and 1 or

more component of cements

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A Classical Example:

Cement-SP Compatibility

Compatibility reflected by concrete rheology

Slu

mp

Time (hrs)

0 1 2

Ideal

Compatible

Incompatible

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7

Common Chemical Admixture Types

• AEA : Air-Entraining

• SRA: Shrinkage-Reducing

• WR: Water-Reducing

• SP: Superplasticizers

• VEA: Viscosity-Enhancing

• Others: Set-Controlling, Corrosion-Inhibiting,

Sealing, etc.

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AEA

Air-Entraining Agent

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9

Air-Entraining Agent (Surfactant)

Hydrophobic chain Hydrophylic head group

(water insoluble) (water soluble)

Anionic – COO-

– SO42-

– SO3-

Ex: Sodium dodecylbenzenesulfonate (DDBS)

CH3

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2 SO3-Na

+

AEA

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Surfactants in Solution and at Interfaces

CMC

Su

rfa

ce

te

nsio

n

6

11

Function of AEA

Promote the

incorporation of air

voids in cementitious

systems for frost

resistance

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SRA

Shringkage-Reducing-Admixtures

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13

SRA

Shringkage-Reducing-Admixtures

Ex: N-Butyl-diEthylene Glycol

SRA

Note: similarity to AEA

CH3

CH2

CH2

CH2

O

CH2

CH2

O

CH2

CH2

OH

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Function of SRA

SRA

SRA’s reduce surface tension thus

reduce capillary pressure and internal strain

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Water Reducers and

Superplasticizers

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Poly Naphthalene Sulfonate (PNS)

CH2

SO3Na

n

PNS

-

--

- - - -

- --

--

----

-

----

-- -PNS

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Lignosulfonate

and Poly Melamine Sulfonate

O

H3CO

O

OH

H3CO

SO3Na

HO

n

N N

N NHNH

HN

O

SO3Na

n

PMS

LS

SO3Na

SO3Na

LS / PMS

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Polycarboxylate

*

*

ONaO O O

O

CH3

n m

p

- - - - - - -

PC

10

19

PNS type PC type

--

--

-

------

- ---

--

-

---

-

-

---

-

-

---

-

-

--- --

---

-

-

-

- --

-

-

-

-

-

--

--- - -

--

-

-

---

-

-

--

- ----

----

- --

---

--

--

---

Mode of Action of SP

Adsorption Electrical charging

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--

- ----

----

--

-

-

---

----

--

---- --

----

----

-- -

- -

--- - - - -

---

--

--

- --

--

-

-

-

Mode of Action of PNS, PMS and Ligno

Electrostatic (mostly) and Steric repulsions

Inducing Particle-Particle repulsion

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Mode of Action of PC

Inducing Particle-Particle repulsion

Electrostatic Steric

Mostly steric repulsion

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Mode of Action of PC

Control of nucleation and growth processes

Heterogeneous

(Topochemical)

Homogeneous

(from solution)

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Floculated Defloculated Dispersed in less water

Defloculating effect of SP operative in any slurry or paste

High fluidity Intermediate fluidityLow fluidity

Function of Superplasticizers

Deflocculation and Dispersion

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Illustration of SP Dispersion Effect

Cement Paste+10 % water +0.1 wt% PNS

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VEA

Viscosity-Enhancing-Admixtures

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VEA

Viscosity-Enhancing-Admixtures

Cellulose

Welan Gum

Starch

-

--

--

VEA

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VEA in Action

Water retention by

adsorption and swelling

Formation of gel network by

polymer molecules

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VEA in Action

Polymer hydration and

particle bridging

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Function of VEA

VEA prevent bleeding and segregation in concrete

VEA

Water retention and immobilization of fines

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Illustration of Different Admixture Types

1 X 10 X 1000 X

SRA

- - - - - - -

PC

-

--

- - - -- -

--

--

---

----

--

- -PNS

Note approximate relative

Size, Charge density and Hydrophilic character

AEA

LS/PMS

-

--

--

VEA

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Compatibility / Incompatibility

Manifestations of Admixture-Admixture

Incompatibilities

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SP – AEA CompatibilityExcess entrained air, increasing with time

S. Moffat-Bergeron and R. Gagne, 2008

Concrete W/C 0.45 – 35MPa

0

2

4

6

8

10

12

14

16

0 200 400 600

AEA (ml/100 kg cement)

Air

at

10

min

(%

)

PC

PNS

No SP

0

2

4

6

8

10

12

14

16

0 20 40 60

Time (min)

Air

(%

)

17

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VEA – SP Compatibility (bleeding)

Welan Methocel

N. Mikanovic and C. Jolicoeur, unpublished, 2006

Cement paste, W/C 0.65

0

20

40

60

80

0 0.02 0.04 0.06

VEA dosage (%)

Ble

ed

(m

l)

PNS

PC

0

20

40

60

80

0 0.05 0.1 0.15

VEA dosage (%)

Ble

ed

(m

l)

PNS

PC

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VEA – SP Compatibility (stability)

Welan Methocel

Cement paste, W/C 0.65

N. Mikanovic and C. Jolicoeur, unpublished, 2006

0.5

0.6

0.7

0.8

0.9

1

0 0.02 0.04 0.06

VEA dosage (%)

Sta

bil

ity

PNS

PC0.6

0.7

0.8

0.9

1

0 0.05 0.1 0.15

VEA dosage (%)

Sta

bil

ity

PNS

PC

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SP / WR performance

PC (0.3% dry)

LS

PNS 0.4%

PMS

Coppola, p203, ACI-SP173, 1997

Dosage = 1% wet basis; Concrete

0

50

100

150

200

250

300

0 25 50 75

Time (min)

Slu

mp

(m

m)

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0

50

100

150

200

250

0 25 50 75 100PC (%)

Slu

mp

(m

m)

PC - SP Compatibility in Mixtures

5 min

Coppola, p203, ACI-SP173, 1997

Dosage = 1% wet basis; Concrete

PNS

LS

PMS

0

50

100

150

200

250

0 25 50 75 100PC (%)

Slu

mp

(m

m)

30 min

LS

PMS

PNS

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Compatibility / Incompatibility

Manifestations of Cement - Admixture

Incompatibilities

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Cement – AEA Compatibility

Surfactant

Na salt

Formula CMC of Na

salt (mM)

Solubility of

Ca salt (mM)

n-Octanoate n-C7H15COONa 345 9.5 (20°)

n-Nonanoate n-C8 230 3.95 (20°)

n-Decanoate n-C9 95 1.31

n-Undecanoate n-C10 50 0.12

n-Dodecanoate n-C11 25 0.09 (15°)

n-Octyl sulfonate n-C8H17SO3Na 148 na

n-Decyl sulfonate n-C10 40 3.21

n-Dodecyl sulfonate n-C12 9.8 0.2

n-Octyl sulfate n-C8H17OSO3Na 130 na

n-Decyl sulfate n-C10 33 na

n-Dodecyl sulfate n-C12 8.2 4.57 (50°)

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Comparative Performance of AEA Series

0

5

10

15

20

25

30

35

0 5 10 15 20

Surfactant (mM)

% A

ir a

t 36 m

in

C10SO3, C10SO4

C8SO3, C8SO4

C12SO4

C7, 8,

9COOC11COO

40

0.00

0.50

1.00

1.50

2.00

2.50

6 8 10 12 14

Number of carbons

- L

og

[C

MC

(M

)]

Lo

g [

so

lub

ilit

y (

M)]

RCOO-

0.00

0.50

1.00

1.50

2.00

2.50

- L

og

[C

MC

(M

)]

-4.50

-4.00

-3.50

-3.00

-2.50

-2.00

6 8 10 12 14

Number of carbons

Lo

g [

so

lub

ilit

y (

M)]

Comparative Performance of AEA Series

Maximum AE at intermediate

chain length

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0

1

2

3

4

5

6

7

8

9

0 10 20 30 40 50 60

% Over-fluidification%

of

PC

-in

i. a

ds

Over-Fluiditification with PC Superplasticizers

Regnaud et al, p389, ACI-SP239, 2006

Mortar, W/C 0.4; PC 0.16% Paste, W/C 0.5; PC 0.16%

30°C

20°C

10°C

Weak PC cement-binding and variable fluidification

200

220

240

260

280

300

320

340

0 10 20 30 40

Time (min)

Sp

rea

d (

mm

)

Over-fluidification

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Cement – Admixture

Sulfate-related Incompatibility

SO4

consumption in

hydration

products

SO4

Buffer

solution

SO4

supply

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w/o SO4 2C3A + 21H C4AH13 + C2AH8 ... CAH

with SO4 C3A + 3CSH2 + 26H C6AS3H32 (Aft)

2C3A + C6AS3H32 + 4H 3C4ASH12 (Afm)

Sulfate supply

Available in solution from: - CaSO4•xH2O

- Na2SO4, K2SO4

Sulfate demand

C3A - amount Ettringite (Aft)

- reactivity Monosulfoaluminate (Afm)

Sulfate balance

Supply / Demand Critical Equilibrium

Crucial Role of Sulfate in C3A Hydration

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CaSO4 form Solubility g/100 g

CaSO4·0 H2O 0.63anhydrite

CaSO4·½ H2O 0.71hemihydrate

CaSO4·2 H2O 0.21dihydrate,gypsum

Portland Cements:

Clinker + (x%) Ca Sulfates

Type C2S C3S C3A C4AF

I 25 50 12 8

II 30 45 7 12

III 15 60 10 8

IV 50 25 5 12

V 40 40 4 10

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SO4 Supply / Demand Equilibrium

SO4/C3A Too low Balanced Too high

Product

formed

CAH gel Ettringite Secondary

gypsum

Behaviour

of concrete

Flash set rapid,

irreversible loss

of slump

Controlled C3A

hydration,

adequate

slump

retention

False set

rapid,

reversible

slump loss

SO4 / C3A Ratio (in first min-hrs)

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C2S

C3S

C3A

C4AF

Competitive adsorption

of PNS and SO4 at

most reactive sites

of cement particles

Cement – Admixture

Sulfate-related Incompatibility

SO4

SO4

SO4

SO4

SO4

SO4

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0

2

4

6

8

10

12

0 0.5 1

PNS Adsorption and Sulfate Competition

C3S

0

100

200

300

0 0.5 1

[PNS]soln (wt%)

C4AF

+Na2SO4

+CaSO4

.1/2 H2O

PN

Sad

s(m

g/g

)

0

100

200

300

0 0.5 1

PN

Sa

ds (

mg

/g)

C3A

+Na2SO4

+CaSO4

.1/2 H2O

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Sulfate Deficient Cement

High PNS Adsorption

Min

i-slu

mp

are

a a

t 3

0m

in

With Na2SO4 : PNS adsorption

Slump area

Adsorbed PNS (%)

C1 C5 C6

Kim et al, Cem. Conc. Res., 30, p. 887-983, 2000

Addition of SO4 (Na2SO4)

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0

2

4

6

8

10

12

0.0 0.2 0.4

Sulfate (mol/L)

Re

lati

ve

flo

w a

rea

, G

0.0

0.2

0.4

0.6

0.8

1.0

Ad

so

rpti

on

ra

tio

RFAds

0

2

4

6

8

10

12

0 0.2 0.4

Sulfate (mol/L)

Re

lati

ve

flo

w a

rea

, G

0.0

0.2

0.4

0.6

0.8

1.0

Ad

so

rpti

on

ra

tio

Sulfate-Balanced Cement

PNS PC

Yamada, p367, ACI-SP195, 2000

Influence of Sulfate on

PNS or PC Adsorption and Paste Fluidity

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C3A(C4AF)

• Low SO4 in solution

• SP(SO3) excessively bound

• Formation of ettringite (modified) strongly repressed

• Rapid loss of fluidity

SP(SO3)CaSO4•xH2O

K2SO4, Na2SO4

Illustration of Cement-SP Incompatibility

Due to Sulfate Deficiency

SO4

Modified ettringite

incorporating SP

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C3A(C4AF)

• SP inhibits growth of

gypsum (syngenite)

SP(SO3)CaSO4•xH2O

K2SO4, Na2SO4SO4

Excess SO4 in soln

• Extensive precipitation of

gypsum (or syngenite)

• Rapid loss of fluidity

Illustration of Cement-SP IncompatibilityDue to Excess Sulfate

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SP adsorption

• C3A content

• C3A reactivity (type)

• Cement fineness

• SP molecular properties

SO4 balance in solution

• Type of CaSO4 (G, H, A)

• Alkali sulfate content

• Ettringite formation (rate, type)

• Gypsum (syngenite) precipitation

C3A(C4AF)

Origin of Cement-SP Incompatibility

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Avoiding Incompatibility Situations

through

• Adequate specification/qualification of the cement,

SCM’s, aggregates

• Relevant characterization of the molecular properties of

the admixtures (and variability in the latter)

• Better understanding on the mode of action of the

admixtures in order to anticipate incompatibility issues

• Development of more «robust» chemical admixtures, or

combinations of admixtures; examples with sulfonated PC

• Extensive quality control and concrete testing.

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