12. Kolloquium und Workshop über„Rheologische Messungen an mineralischen

Baustoffen“12. und 13.März 2003 in Regensburg

Testing compatibility of cement - superplasticizer

system Jacek Gołaszewski, Janusz SzwabowskiSilesian University of Technology, Gliwice, Poland

Introduction

The main trend in concrete technology is to produce concrete of high strength, durability and reliability.

Production of such a concrete cause technological problems.

These problems are a result of conflict between requires high workability (high W/C) and requires high strength and durability (low W/C). W/C ratio

Co

mp

ress

ive

str

en

gth

Fresh concrete w ithout SP

Hand compacting

Fresh concrete w ithout SPVibration

Fresh concrete w ith SPVibration

Concrete totally compacted

Concrete unsatisfactory compacted

Introduction

Superplasticizers make possible to solve this conflict - its addition allow to obtain required workability of low W/C fresh concrete.

The key element in efficient workability shaping is to find out cement superplasticizer compatible system and the complex knowledge on rheological effects of superplasticizer addition. W/C ratio

Co

mp

ress

ive

str

en

gth

Fresh concrete w ithout SP

Hand compacting

Fresh concrete w ithout SPVibration

Fresh concrete w ith SPVibration

Concrete totally compacted

Concrete unsatisfactory compacted

Introduction

In the paper methodology of testing of superplasticizer performance using workability two point test is presented and some effects of cement composition on rheological properties of superplasticized mortars are discussed.

W/C ratio

Co

mp

ress

ive

str

en

gth

Fresh concrete w ithout SP

Hand compacting

Fresh concrete w ithout SPVibration

Fresh concrete w ith SPVibration

Concrete totally compacted

Concrete unsatisfactory compacted

Workability - traditional approach

Workability is a physical property of fresh concrete alone and define its ability on applied methods of transport,

placing and compacting without segregation

Workability - rheological approach

The definition of workability in concrete technology should be considered in terms of the state of the system.

MICRORHEOLOGICALCONNECTIONS

MACRORHEOLOGICALCONNECTIONS

WORKABILITY RELATION

FROM MIX POINT OF VIEWFROM METHOD POINT OF VIEW

MIXCOMPOSITION

STRUCTUREOF MIXSTATUS

TYPE OFPROCESS

REALIZATIONMETHOD OFPROCESS

SYSTEM OFEXTERNAL FORCES

RHEOLOGICALPROPERTIES OF MIX

Workability - rheological approach

This state is determined by the relationship between two factors: (1) the rheological properties of given mix and(2) the forces acting on it during processing.

MICRORHEOLOGICALCONNECTIONS

MACRORHEOLOGICALCONNECTIONS

WORKABILITY RELATION

FROM MIX POINT OF VIEWFROM METHOD POINT OF VIEW

MIXCOMPOSITION

STRUCTUREOF MIXSTATUS

TYPE OFPROCESS

REALIZATIONMETHOD OFPROCESS

SYSTEM OFEXTERNAL FORCES

RHEOLOGICALPROPERTIES OF MIX

Workability - rheological approach

Therefore, concrete mix workability is determined by the reaction of the mix to the forces acting on it during transport and mechanical processing as the resistance of its structure to these forces.

MICRORHEOLOGICALCONNECTIONS

MACRORHEOLOGICALCONNECTIONS

WORKABILITY RELATION

FROM MIX POINT OF VIEWFROM METHOD POINT OF VIEW

MIXCOMPOSITION

STRUCTUREOF MIXSTATUS

TYPE OFPROCESS

REALIZATIONMETHOD OFPROCESS

SYSTEM OFEXTERNAL FORCES

RHEOLOGICALPROPERTIES OF MIX

Workability - rheological approach

Required workability can be achieved: (1) to the given method and conditions of concrete processing rheological properties of concrete mix are adjusted or (2) to given rheological properties of concrete mix method and conditions of concrete processing are adjusted.

MICRORHEOLOGICALCONNECTIONS

MACRORHEOLOGICALCONNECTIONS

WORKABILITY RELATION

FROM MIX POINT OF VIEWFROM METHOD POINT OF VIEW

MIXCOMPOSITION

STRUCTUREOF MIXSTATUS

TYPE OFPROCESS

REALIZATIONMETHOD OFPROCESS

SYSTEM OFEXTERNAL FORCES

RHEOLOGICALPROPERTIES OF MIX

Rheological model of fresh concrete

Fresh concrete (and also fresh mortars), behaves as bingham body, whose properties can be expressed by the two fundamental rheological parameters, the yield stress and the plastic viscosity according the formula:

where (Pa) is the shear stress at shear rate (1/s) o (Pa) is the yield value

(Pas) is the plastic viscosity. The physical interpretation of yield value is that of the stress needed

to be applied to a material in order to start flowing. When the shear stress is higher then the yield value the mix flows and its flow

resistance depends on plastic viscosity.

o

Factors influencing rheological properties of fresh concrete - key role of superplasticizer

W/C ratio SuperplasticizerCement AdmixturesAdditives

Watercontent

Cementpaste

content

Cement - SPinteraction

Rheologicalproperties ofconcrete mix

Superplasticizeraddition method

Superplasticizerdosage

Aggregate

Temperature

Testing of superplasticizer performance

The key elements in efficient workability shaping using superplasticizers are: to find out the compatible cement -

superplasticizer system; to know how addition of superplasticizer

influences the rheological properties of fresh concrete in different technological conditions.

Conventional vs. Rheometrical workability tests

CONVENTIONAL WORKABILITY TESTS

conventionality – simulate only specific methods of concreting;

physically ambiguous – there is no correlation between results of measurements and rheological parameters of concrete mix;

limited measurement range - (slump test, Marsh cone test) - one point measurement;

ambiguous measurements - the results of measurement of mixes of different rheological parameters can be the same

RHEOMETRICAL WORKABILITY TEST

unequivocal – measurements basing on physical principles;

physically unequivocal – measurements results expressed in physical units;

full measurement range - two point measurement;

unequivocal measurements results – makes possible physical and statistical analysis and computer simulation of fresh concrete behaviour during concreting process.

Rheometrical Workability Test

Measurement of shear resistance of fresh concrete mix in function of time in order to determine

rheological parameters of mix and changes of these parameters in respect to technological

factors (mix composition, time, temperature).

Rheometrical workability test

Rheological parameters of fresh concrete are measured by applying a given shear rate (rotation rate N of paddle or probe) and the measuring the resulting shear stress (torque T). The rheological parameters are determined by regression analysis according to the relation:

T = g + N hwhere g constant corresponding to yield value o

h constant corresponding to plastic

viscosity . 0

20

40

60

80

100

120

0 50 100 150 200

N [1/min]

T [N

mm

]

g = 33,93 Nmmh = 0,136 Nmmminr = 0,990Bwg = 2,79%Bwh = 6,82

y = 0,138 x + 33,93

Rheometrical workability test - what kind of mix to be used?

Cement paste - most popular in testing cement - SP compatibility, easy to manage but due differences between rheology of cement paste and fresh concrete mix and problems with proper interpretation of results gives ambiguous information on influence of superplasticizer on rheological parameters.

Fresh concrete - difficult to manage (due cost of apparatus and material and labour consumption), due changeable grading of aggregate proper interpretation of superplasticizer performance is difficult.

Fresh mortar - model of concrete, using CEN model sand effect of changeable aggregate grading can be eliminated, easy to manage, makes possible to chose compatible cement - SP system and gives qualitative information of superplasticizer performance useful for workability shaping.

Rheometrical workability test

0

20

40

60

80

100

120

140

160

0 10 20 30 40 50 60 70

Time [min]

To

rqu

e [

Nm

m]

g dg h dh r

po 10 minutach 25,55 18,80% 0,811 7,80% 0,988po 60 minutach 46,66 9,31% 0,780 6,71% 0,991

0

40

80

120

160

0 10 20 30 40 50 60 70Time [min]

Ro

tati

on

al s

pe

ed

[1/

min

]

Testing procedure and example of measurement

Effect of cement composition on rheological properties of mortars

In the research following factors were investigated: mineral and chemical composition of cement

C3A 2%; 7%; 12%;

Na2Oeq 0,3%; 0,7%; 1,1%;

SO3 2,5%; 3,0%; 3,5%

cement specific surface 320; 370; 420 m2/kg SP type 6 SP SNF, SMF, PC, PE1, PE2, PE3 W/C ratio 0,55; 0,45; SP dosage 1%; 2% i 3% m. C

Mortars were prepared and tested according PN EN 196-1:1996 and PN EN 934-2:1999.

Effect of cement specific surface and composition on rheological properties of mortarsW/C=0,55

0

20

40

60

80

100

120

0 4 8 12

C3A [%]

g [

Nm

m]

0

0,1

0,2

0,3

0,4

0,5

0 4 8 12C3A [%]

h [

Nm

mm

in]

Na2Oeq-0,3%; 320 m2/kgNa2Oeq-0,3%; 370 m2/kgNa2Oeq-0,3%; 420 m2/kgNa2Oeq-0,7%; 320 m2/kgNa2Oeq-0,7%; 370 m2/kgNa2Oeq-0,7%; 420 m2/kgNa2Oeq-1,1%; 320 m2/kgNa2Oeq-1,1%; 370 m2/kgNa2Oeq-1,1%; 420 m2/kg

Effect of cement specific surface and composition on rheological properties of mortarsW/C=0,55; SP PE1; 1%

0

20

40

60

80

100

120

0 4 8 12

C3A [%]

g [

Nm

m]

0

0,1

0,2

0,3

0,4

0,5

0 4 8 12C3A [%]

h [

Nm

mm

in]

Na2Oeq-0,3%; 320 m2/kgNa2Oeq-0,3%; 370 m2/kgNa2Oeq-0,3%; 420 m2/kgNa2Oeq-0,7%; 320 m2/kgNa2Oeq-0,7%; 370 m2/kgNa2Oeq-0,7%; 420 m2/kgNa2Oeq-1,1%; 320 m2/kgNa2Oeq-1,1%; 370 m2/kgNa2Oeq-1,1%; 420 m2/kg

Effect of cement specific surface and composition on rheological properties of mortarsW/C=0,45; SP PE1; 3%

0

0,1

0,2

0,3

0,4

0,5

0 4 8 12C3A [%]

h [

Nm

mm

in]

0

20

40

60

80

100

120

0 4 8 12

C3A [%]

g [

Nm

m]

Na2Oeq-0,3%; 320 m2/kgNa2Oeq-0,3%; 370 m2/kgNa2Oeq-0,3%; 420 m2/kgNa2Oeq-0,7%; 320 m2/kgNa2Oeq-0,7%; 370 m2/kgNa2Oeq-0,7%; 420 m2/kgNa2Oeq-1,1%; 320 m2/kgNa2Oeq-1,1%; 370 m2/kgNa2Oeq-1,1%; 420 m2/kg

Effect of cement composition on rate of changes of rheological parameters of mortars in timeW/C=0,55; W/C= 0,55; SP PE1; 1%; W/C=0,45; SP PE1; 3%

-0,5

0

0,5

1

1,5

0 4 8 12C3A [%]

dg

/dt [

Nm

m/m

in]

-5

-4

-3

-2

-1

0

1

0 4 8 12C3A [%]

dh/d

t [N

mm

min

/min

*E-3

]

Na2Oeq-0,3%

Na2Oeq-0,7%

Na2Oeq-1,1%

Na2Oeq-0,3%

Na2Oeq-0,7%

Na2Oeq-1,1%

Na2Oeq-0,3%

Na2Oeq-0,7%

Na2Oeq-1,1%

W/C=0,55

W/C=0,55;SP-1%

W/C=0,45;SP-3%

Effect of cement composition on rheological properties of mortarsW/C=0,55; SP PE1 1%; SP SNF 2%; SP SMF 2%

0

20

40

60

80

100

120

0 4 8 12Ilość C3A [%]

g [

Nm

m]

0

0,1

0,2

0,3

0,4

0,5

0 4 8 12C3A [%]

h [

Nm

mm

in]

Na2Oeq-0,3%Na2Oeq-0,7%Na2Oeq-1,1%Na2Oeq-0,3%Na2Oeq-0,7%Na2Oeq-1,1%Na2Oeq-0,3%Na2Oeq-0,7%Na2Oeq-1,1%

PE1

SNF

SMF

Effect of cement composition on rheological properties of mortarsW/C=0,45; SP PE2 2%; SP PE3 2%; SP PC 2% (after 10 min)

0

20

40

60

80

100

120

0 4 8 12C3A [%]

g [

Nm

m]

Na2Oeq-0,3%

Na2Oeq-0,7%

Na2Oeq-1,1%

Na2Oeq-0,3%

Na2Oeq-0,7%

Na2Oeq-1,1%

Na2Oeq-0,3%

Na2Oeq-0,7%

Na2Oeq-1,1%

PE2

PE3

PC

0

0,1

0,2

0,3

0,4

0,5

0 4 8 12C3A [%]

h [

Nm

mm

in]

Effect of cement composition on rheological properties of mortarsW/C=0,45; SP PE2 2%; SP PE3 2%; SP PC 2% (after 60 min)

0

0,1

0,2

0,3

0,4

0,5

0 4 8 12C3A [%]

h [

Nm

mm

in]

0

20

40

60

80

100

120

0 4 8 12C3A [%]

g [

Nm

m]

Na2Oeq-0,3%

Na2Oeq-0,7%

Na2Oeq-1,1%

Na2Oeq-0,3%

Na2Oeq-0,7%

Na2Oeq-1,1%

Na2Oeq-0,3%

Na2Oeq-0,7%

Na2Oeq-1,1%

PE2

PE3

PC

Summary Through the investigation with RWT it is possible to precisely

determine the influence of superplasticizers on the rheological properties of mortars. On the ground of this it is possible to choose compatible cement - superplasticizer system and optimise the composition of mortar and concrete from workability point of view.

The type, chemical and phase composition of the cement are the decisive factors for the performance of superplasticizers. General relationships between cement properties and rheological parameters of no- and superplasticized mortars are discussed in paper.

Testing properties of mortars using RWT it is possible to recognise how other admixtures and additives as: air entraining agents, accelerators, retarders, silica fume, fly ashes, slags affecting rheological properties of fresh concretes in different technological conditions.