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International Conference on Advances in Concrete Technology and Sustainability Issues, January 11. 2012, Quito, Ecuador Slide 1 of 36

Prepared for the International Conference on Advances in ConcreteTechnology and Sustainability Issues

January 11, 2012, Quito, Ecuador


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Compatibility and Incompatibility

Compatibility:

Every admixture present in a cementitious mixtureperforms its expected role without negative effects

Incompatibility:

Upon addition of admixture the concrete mixturedoes not behave as expected

The effects of admixtures can be:

detrimental(one or more admixtures do notperform as expected), or synergistic(combinationof admixtures performs better than when used

separately)


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Robustness

The Robust system small variations in the

dosage of cement, water or admixture havelittle effect on the properties of the mixture

The Non-Robustsystem small variationsin the cement, water or admixture dosageresult in significant (sometimes dramatic)

changes in concrete properties


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Courtesy of Csar A. Constantino, Titan America

Introduction

Lack of in-depth

knowledge of thematerialsinteractions maylead to

incompatibilitiesbetween variousingredients of the

mixture.


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Admixture - Cementitious Materials

Interactions

Admixtures interact with components of

cementitious materials and influence cementhydration

Effects depend on:

Type and dosage

Composition

Sequence of addition

w/cm and temperature

Compatibility of admixtures (mixtures of admixtures)

Chemistry and specific surface area of cem. mat.

Courtesy of PCA


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Background.

Materials incompatibility problems do not

occur in every concrete mixture. However,

when they arise, concrete may experience

undesirable effects, primarily prematurestiffening or severe set retardation.

In addition, difficulties with creating anadequate air void system may be

experienced, resulting in durability problems.


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Types of Incompatibilities

Resulting from Direct Interactions

Cement-Admixture interaction Admixture-Admixture interaction

Resulting from Indirect Interactions

Typically involve interactions between 2 (ormore) admixtures and 1 or more component ofcementitious system


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General Trends

Role of C3A:

Uncontrolled hydration of C3A is the major

reason for early stiffening behavior flash set.Delays setting time by preventing hydration of

silicates

Role of sulfates:Sulfate deficient systems - the rapid

hydration of C3A - flash set

Excessive sulfate nucleation and growth ofgypsum crystals - false setting behavior.

The level of soluble sulfates affectsadsorption of admixtures


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General Trends

Role of alkalis:

Higher alkali cements react faster higherrate of stiffening higher slump loss

Dosage requirement of admixtures are

directly related to alkali content of thesystem.

Low alkali content systems exhibited lowerstability of air void system.

Low alkali cement & synthetic air entrainercombination resulted in severe strength loss


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General Trends

Role of Fly Ashes:

May introduce reactive aluminate phases(like C3A and Kleins compound)Sulfates and alkalis in fly ash - disturb the

sulfate balanceHigh LOI class F (low lime) ashes

problems with generation and stability of airvoidsCalcium and magnesium ions in the fly ash

affect the air entrainment precipitates withAEAs


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General Trends

Role of Admixtures:

High alkali contents -increase the amount ofpolycarboxylate type of superplasticizers -optimum fluidityLignin based admixtures reduce the solubility

of sulfates thus disturbing the C3A sulfatebalanceSugar content of the lignin based, water-

reducers linked to set retardation and air

entrainment difficultiesVR + Lignin based WRA - high entrapped air &

reduction in specific surface area of the airvoid system


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Stages in Hydration Reaction

Iinitial hydration processes (015 min); IIinduction period (15 min4 h); IIIacceleration and setting (48 h); IVdeceleration and hardening (824 h);

Vcuring beyond 1 day.

Jolicoeur et al. 1994, ACI SP-148,pp. 63-88

Solubilization

of cementphases

Cement particles

become coatedwith layer ofhydrates

Critical role ofreactions of

aluminate andgypsum phases


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Admixture-binder Interactions

Admixtures that modify the properties of

fresh concrete

may cause early stiffeningor retardation of the setting time.

Early stiffening is often caused by changes

in the rate of reaction between tricalciumaluminate (C3A) and sulfate in the cement.

Retardation can result from an overdose ofadmixture or from a decrease in the ambienttemperature. Both delay calcium silicates

hydration.


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Example: Change in the Rate of

Hydration

Jolicoeur et al. 1994, ACI SP-148,pp. 63-88

Change in the rate of hydration at three different dosages of chemical admixture


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Critical Role of Sulfate in Controlling

Hydration of C3A

Courtesy of C. Jolicoeur


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Forms of Sulfates

Forms of CaSO4 Solubility (g/100g)

CaSO4 . 0 H20Anhydrite*

0.63

CaSO4 . 1/2 H20

Hemihydrate0.71

CaSO4 . 2 H20Dihydate (gypsum)

0.21

K2SO4, Na2SO4 Highly soluble*Anhydrite can be synthetic (soluble) and natural (less soluble) .

Natural anhydrite has slower rate of solution than gypsum, hemihydrate orsynthetic (soluble) anhydrite


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SO4 Supply/Demand Equilibrium



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Superplasticizing Chemicals

Class Origin Structure (typical repeat unit)

Lignosulphonates

Derived fromneutralization,

precipitation, and

fermentation processes

of the waste liquor

obtained duringproduction of paper-

making pulp from woodSulphonated

melamine

formaldehyde (SMF)

or Polymelaminesulfonate (PMS)

Manufactured by normal

resinification of

melamine -formaldehyde


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Superplasticizing Chemicals

Class Origin Structure (Typical Repear Unit)

Sulphonated

naphthalene

formaldehyde (SNF)

or Polynaphtalene

Sulfonate (PNS)

Produced from

naphthalene by oleum orSO3sulphonation;

subsequent reaction with

formaldehyde leads to

polymerization and the

sulphonic acid isneutralized with sodium

hydroxide or limePolycarboxylic ether

(PCE) orPolycarboxylate

(PC type)

Free radical mechanism

using peroxide initiators isused for polymerization

process in these systems


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Sulfate related Cement Admixture

Incompatibility



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Effect of Calcium Lignosulfonate (CLS)

Dodson, V. 1990. Concrete admixtures,


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PNS adsorption vs. Sulfate Content


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Role of Alkalis

The soluble alkali content is a key

parameter when studying the compatibilitybetween a cement and a superplasticizer,

The addition of a small amount of sodium

sulfate can reduce the slump loss of asuperplasticized cement paste.


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Compatibility between cements and PNS

and relation to adsorption behavior

Alkalies C1 C2 C3 C4 C5 C6Na2O eq. 0.31 0.52 0.92 0.74 0.35 0.31

Soluble Alkalies 0.19 0.41 0.57 0.72 0.07 0.06

B.-G. Kim et al. / Cement and Concrete Research 30 (2000) 887893

P f PNS d b d d i i l


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Percent of PNS adsorbed and mini-slump areaat 30 min for cement pastes with various

Na2SO4 contents.

Alkalies C1 C5 C6

Na2O eq. 0.31 0.35 0.31

SolubleAlkalies

0.19 0.07 0.06


P t f PNS d b d d i i l


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Percent of PNS adsorbed and mini-slump areaat 30 min for cement pastes with various

Na2SO4 contents.



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Example of multi-source interactions

Potential incompatibility problems arising in

the cementitious systems containing broadcollection of cements, fly ashes and

chemical admixtures.

Focus on abnormal early age stiffening,

setting behavior and quality of the air voidsystem.


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Properties Fly ashesF1 Class C ash F2 Class C ash F3 Class F ash

LOI 0.38 (M) 0.25(L) 3.89(H)

SO3 0.53(M) 1.14(H) 0.69(M)

Na2Oeqv 2.18(M) 1.94(M) 2.21(M)

Chemical

propertiesCements

C1 C2 C3 C4

C3A % 9 (M) 10(M) 10.1(M) 7.7(L)

SO3% 3.0(M) 2.4(L) 3.6(H) 3.6(H)

Na2Oeqv% 0.29(L) 0.3(L) 1.04(H) 0.97(H)


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Chemical Admixtures

Water Reducing Admixtures: (WRA)

Lignin based Type A WRA (W1)

Polycarboxylate Type F superplasticizer (W2)

Air Entraining Admixtures: (AEA)

Synthetic AEA (A1) Vinsol resin (VR) based AEA (A2)


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Work Plan

PHASE IIIPHASE IIPHASE I

Study related torapid slump loss and

abnormal setMore than 100paste and mortarmixtures evaluated

Study related toproblems with

generation &stabilityof air void system18 mortars andslurries evaluated

Verification offindings from

pastes and mortars10 concretemixtures evaluated

Statistical Modeling DEVELOPMENT OF RECOMMENDATIONS


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Admixture Driven Incompatibilities

W1 + plain C2 severe acceleration while W2 + C2

severe retardation

W1 or W2 + C2 fly ash cementitious system

severe acceleration of set


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Double Dosage of WRA

Aggravated stiffening problem in all the earlystiffening mixtures

Significant changes in SAC curves in 5 out 6mixtures


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Fly Ash Driven Problems

As the fly ash content increased, the amount

of A1 or A2 (required to attain 18+/-2 % air

content) also increased


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Effect of Class C Ash Content

94% of high (>30%) volume fly ash (HVFA) mixtures

significant acceleration of set

70% HVFA mixtures set time less than 45mins


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Steps to Identify Incompatibility

Air Void System:

Air content in mortars(ASTM C 185) or Foamindex testing

Foam drainage testing

New Reactive Materials:

Cement: C3A , sulfate & alkali content SCMs: sulfate% & LOIWRAs & AEAs : Varying chemical nature

Potential incompatible combination ???


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Steps to Mitigate Incompatibility

Vary the following (one or more at a time) and testagain for potential problems.

Air Void System:

Select a fly ash with low LOI

Change the percentage of flyash replacement

Change the type of air

entraining agent (AEA)Change the type of Waterreducing agent (WRA)

Test the new combination for incompatibility

Potentially incompatible combinations???

admixtures olek

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