Impact of Water Reducers and Superplasticizers on...

July 27 – 29, 2009

Ara A. Jeknavorian, Ph.D.

Research Fellow

W.R. Grace – Conn.

Cambridge, MA

Impact of Water Reducers

and Superplasticizers on

the Hydration of Portland

Cement

International Cement Summit Quebec July 2009 2

Outline

General Considerations in Understanding the Impact of WRAs on

Cement Hydration

Common Normal Range and High Range Water Reducing Chemistries

WRA/HRWR performance as a function of the balance between

aluminate reactivity-sulfate availability.

Modeling Challenge: Examples of Cement-Admixture Interactions

Gaps and Opportunities


Normal and high range (superplasticizing) chemical admixtures almost invariably retard the rate of the cement hydration.

For a given cement, this affect can vary significantly depending on:

• Cement/SCM fineness, chemistry, and degree of pre-hydration

• Chemistry of dispersing admixture, especially when formulated with multiple components.

• Admixture addition rate, the time of addition, amount adsorbed by the cement and amount of admixture in the pore water as a function of time.

• Selective and complex cement-admixture interactions.

• Mixture rheology, composition and temperature

The Impact of WRAs on Cement Hydration:

General Considerations


Fate of Chemical Admixture added to Hydrating Cementitious System

What happens to WRAs during the initial minutes of cement

hydration has major consequence on subsequent hydration rate.

Balance between aluminate reactivity and sulfate availability as a

function time control the fate of essentially all chemical admixtures.

Aluminate hydrates have a strong, irreversible adsorption for organic

compounds, and WRAs are no exception.

The workability and impact on setting are far less influenced when

WRAs are adsorbed on aluminate hydrates.

WRAs not adsorbed and intercalated in/on aluminate hydrates, are

available to adsorb on hydrating C3S and ettringite increased

cement dispersion and increased set retardation.


Cement Dispersing Action of Superplasticizers

Increased water

demand

Less than optimum

strength development

Higher particle surface area –increased strength


Common Normal Range Water Reducing Admixtures

Corn Syrup – Hydroxylated PolymerHydroxycarboxylic

acid salts

Sodium GluconateSodium Glucoheptonate O

OH

lignin O lignin

SO3-Ca

2+

Calcium/Sodium lignosulfonate “lignin”


Common High Range Water Reducing Admixtures

SO

3

-Na

+

O

n

Ca/Na Salts of Naphthalene and Melamine Sulfonate Formaldehyde Condensate

Polycarboxylate-Polyether “Comb” Polymer

N

CH2

CHH3C

O

CH2

CH2

H3C

O

CH

CH2

OCH3

NH3

CH2

CHH3C

O

CH2

CH2

H3C

O

CH

CH2

OCH3

OCH3

CH2

CH

O

H3C

CH2

CH2

O

H3C CH

CH2

OC

CHCH2CH2 CH

CO

CH2 CH

C O

NH

CH2 CH

C O

OOH

OC

CHCH2a b c d

x

y

xx

yy

NSFC (SNF)MSFC(SMF)

PC

CH2CH2OCH3 O

R

CHCH2 N

CH2

CH2

PO3H2

PO3H2

( )n

PEG amino di-methylphosphonate

CH CH

C CO O

OH NH

SO3H2

ON

CHCH2( )n

Sulfanilic acid grafted poly-co-alt-(maleic

anhydride-vinylpyrrolidone)


Tee

th l

en

gth

Backbone length

Teeth

density

Polycarboxylates

are to concrete as

designer drugs are

to medicine

Polycarboxylate-Polyether Technology:

Unlimited Possibilities

•Polymer Variables:

- Backbone/teeth length and chemistry

- Teeth density and chemistry


Mortar Flow As a Function of WRA Chemistry Dosage

170

180

190

200

210

220

230

240

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Dosage to Cement (wt%)

Flo

w (

mm

)

ADVSP

NSFC

LIGNIN

Various WRAs can alter the flow of cementitious mixtures over

different dosage ranges, which can strongly impact rate of

cement hydration.

(PC)(PC)


ICCC 2007

Adsorption of Water Reducing Admixtures as a Function of Dosage


MIX DESIGN

Cement Factor 300 kg/m3

Water 160 kg/m3

Fine Aggregate 740 kg/m3

Coarse Aggregate 1040 kg/m3

PC 0.03 - 0.12% s/s

NSFC 0.10 - 0.45% s/s

Lignin 0.10 – 0.35% s/s

Corn Syrup 0.10 - 0.30% s/s

Normalizing Set Time Response of WRAs as a function of Slump


Slump vs Set: Water Reducing Performance in Concrete

0

1

2

3

4

5

6

7

8

9

10

0 2 4 6 8 10 12 14

Set Time, hr.min

Slu

mp

, in

PC

Lignin

Corn syrup

NSFC

Slump vs Set Response for various WRAs

Common normal and high range (superplasticizing) chemical

admixtures almost invariably retard the rate of the cement

hydration process.


Understanding the Complexity of Cement-Admixture Interactions

V.S. Ramachandran, V.M.

Malhotra, C. Jolicoeur,

and N. Spiratos,

“Superplasticizers:

Properties and

applications in

Concrete,” p 178.

Admixture addition rate

Time of addition

Formulation

Temperature

Cement Pre-hydration

Other Factors Affecting Admixture

Adsorption and subsequently Cement

Hydration


Understanding Impact of Aluminate-

Sulfate Balance on Cement

Hydration in Presence of Admixtures


Possible Outcomes: Aluminate-Sulfate Balance

FALSE SET

OK

FLASH SET

Low C3A activity

Gypsum

Gypsum

Medium C3A activity

High C3A activity

Plaster

High C3A activity

Anhydrite

Plaster High C3A activityOK

FLASH SET


Adsorption of NSFC by Various Hydrating Cement Minerals

•V.S. Ramachandran, V.M. Malhotra, C.

Jolicoeur, and N. Spiratos,

“Superplasticizers: Properties and

applications in Concrete,” p 196.


Mix Water Addition Delayed Addition

Adsorption of NSFC as a Function of Addition Mode:

Mix Water vs. Delayed

Far less NSFC adsorbed with delayed addition resulting in improved

dose-slump response and greater impact on cement hydration.V.S. Ramachandran, V.M. Malhotra, C. Jolicoeur, and N. Spiratos, “Superplasticizers: Properties

and applications in Concrete,” p 178.


Water/cement ratio 0.5, 23 C,

water only

Sulfate

depletion

5 Cement Samples

From Same Plant

- with reported

setting time

problems - Tested

Without Admixtures

With Admixtures

Set Time Variations with OPC – with and without Chemical

Admixtures

0.15% WRA [0.10% CS +0.05% TEA]

0.20% MRWR [0.10% PC + 0.05% SG

+ 0.05% Ca(NO3)2]

•

•

•Water/cement ratio 0.5,

•23 C,0.35% water

reducing admixture by

weight of cement in all

samples•


ASTM C359 Early Stiffening of Mortar Test

Detecting Cement – Admixture Incompatibilities

600g cement

600 g sand

w/c = 0.30*

* Revised procedure

calls for variable w/c

50 mm


Step Procedure w/o Admixture Time

1

Add sand and cement, mix 10

sec slow speed

0-10 sec

2 Add water 10-15 sec

3 Mix medium speed 15 sec - 3:15

4 Stop and scrape, measure

temp

3:15 - 4:00

5 Mix medium speed 4:00 - 4:15

Stop, fill ISC vial, place in ISC 4:15 - 4:45

6 Stop, fill container 4:45 - 5:15

7 Initial penetration 5:15

8 Penetration readings 8, 11, and 14

minutes

9 Remix 14 - 15

10 Sop, fill container 15:00 - 15:45

10 Penetration reading 15:45



Modified C 359 ProcedureAdmixture Addition

Modes

Mix Wat 1 min 2 min

Ad’n del. Del.

10 sec

1:15 2:15


Cement 006 017 051 133 143 170

Initial 3 / 24.1 31 / 24.8 50+ / 23.7 50+ / 24.7 50 / 23.4 50+ / 24.5

5 Minutes 1 / 25.6 1 / 25.2 45 / 23.7 50+ / 24.5 45 / 23.2 50 / 24.5

8 Minutes 1 / 25.6 1 / 25.1 29 / 23.5 50+ / 24.5 41 / 22.9 48 / 24.5

11 Minutes 1 / 25.2 0 / 24.6 6 / 23.2 47 / 24.2 10 / 22.8 48 / 24.0

Remix

13 Minutes 2 / 23.6 46 / 23.5 50+ / 21.5 50+ / 23.0 48 / 22.2 50+ / 22.6

16 Minutes 2 / 23.6 38 / 23.5 50 / 21.4 50+ / 23.0 34 / 22.0 50+ / 22.6

ASTM C 359 Early Stiffening Results

w/ Fixed Water Content

(W/C = 0.30)

Penetration in mm / ºC


078 Cement

0

10

20

30

40

50

60

0 5 10 15 20 25

Minutes

Pen

etr

ati

on

, m

m

(mm)

(mm) W64,m

(mm) W64, 1d

(mm) W64, 2d

W64 = LS/CS/TEA, 3 oz/cwt (195 ml/100 kg); 0.10% s/s)

Impact of Delayed Chemical Admixture

Addition on ASTM C359 Mortars


Time vs. Power

0.00E+00

1.00E+00

2.00E+00

3.00E+00

4.00E+00

5.00E+00

6.00E+00

0 5 10 15 20 25 30

Time,hrs.

Po

we

r,m

W/g

078 Blank with 177.0g water

078 Blank with 176.0 water

078 with [email protected] Mix Water

078 with [email protected] 1 Min Delay

078 with [email protected] 2 Min Delay

W64,MW

W64,

1 min del

W64,

2 min del

Control

Isothermal Calorimetry on Mortars with Delayed Admixture Dosages

Note decrease in

initial exotherm


Admixture Mechanisms of Set Retardation

Precipitation of calcium salts on cement surface to re-enforce the

semi-permeable membrane formed during induction period.

Complex formation

- Organic molecules complex with Ca2+ lowering Ca2+ in solution and

reducing growth of Ca(OH)2. However, Ca complexes tend to have

low stability constants, and [Ca2+] in pore water is quite high.

Nucleation

- CH Crystals act as calcium sinks and cause increase in C3S

hydration near end of induction period. Organic compounds can

delay nucleation and growth of CH, thus causing retardation.

However, chemical admixtures are rarely single

component formulations.


Impact of Cement Prehydration on

Retarding Effect with WRAs


Impact of Cement Prehydration on Retarding Effect of WRAs

Setting

indicator

Cement Admixture Dose,

oz/cwt

Graph

078-I/II, Fresh CS/LS 3

078-I/II, Fresh

078-I/II, Fresh

078-I/II, Fresh

078-I/II, 50% RH @16 hr

078-I/II, 50% RH @16 hr

078-I/II, 50% RH @16 hr

078-I/II, 50% RH @16 hr

Gluconate/Sugar

CS/TEA

LS/CS/TEA

CS/LS

Gluconate/Sugar

CS/TEA

LS/CS/TEA

3

4

4

3

3

4

4

CS/LS

Gluconate/

sugar


Effect of Prehydration on Cement-Admixture Interactions

Cement was spread out in a ½ inch layer in the shrinkage lab, 72 F @ 50% RH

We initially found strong effect of 16 hours prehydration on the retardation of 078 cement with certain admixtures.

No effect visible by LOI, TG, XRD or optical microscopy, confirming that the extent of prehydration was very mild.

Significant prehydration is easily visible by TG, optical microscopy, and is known to alter the hydration of cement in presence of admixture.

Additional retardation by prehydration of 078 cement

with 3 oz/cwt Lignin/Corn Syrup Blend dosed upfront

0

2

4

6

8

10

12

14

16

18

20

0 16 72Hours prehydration @ 50% RH

Incre

me

nta

l re

tard

ati

on

by

pre

hyd

rati

on

, h

ou

rs


Time to Initial Set with Slag 100

4.0

5.0

6.0

7.0

8.0

0% Slag

(0.13% s/c)

16% Slag

(0.11% s/c)

16% Slag

(0.15% s/c)

40% Slag

(0.11% s/c)

40% Slag

(0.15% s/c)

(Avg of Two Proctors)

Tim

e (

Hrs

.)

Effect of PC Type and Slag Content on Set Time

PC1 (Short “teeth”)

PC 500 (Long “teeth)


Conduction Calorimetry, [email protected]%

Effect of PCE Structure, Dose on Cement Hydration

Onset of early Cement Hydration can be controlled with

selected PCE compositions: smaller the surface footprint,

earlier the onset of hydration.

PCE Co-polymer MPEG-MA

m:n = 1.2, 1.4, 1.6, p=23, 102

ICCC 2007


Knowledge Gaps and Opportunities

Admixture adsorption by aluminate versus

silicate phases

Impact of cement pre-hydration and hydration

rate associated with chemical admixtures

Performance from delayed admixture addition

more predictable versus mix water addition?


Possibilities for Predicting Admixture Performance

in Cementitious Systems

Considering the multitude of factors, coupled with the variation

in those factors, that can effect the interaction of portland

cements with water reducing chemical admixtures, modeling

cement hydration in the presence of admixtures – on the basis of

material characterization - would appear to be a very difficult

challenge.

A model for predicting the impact of chemical admixtures on

cement hydration may be possible by measuring the

performance of chemical admixtures with several selected, well

characterized cements. The resulting performance indexes (i.e.

isothermal calorimetry coupled with paste or mortar rheology)

could be predictors with a wide range of cements.

Impact of Water Reducers and Superplasticizers on...

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