The air-entraining methodology decrease

of self-compacting concrete

Prof. dr hab. inż. Janusz SzwabowskiDr inż. Beata Łaźniewska-Piekarczyk

Silesian University of Technology, Gliwice, Poland,e-mail: Janusz.Szwabowski@polsl.ple-mail: Beata.Lazniewska@polsl.pl

17. Kolloquium und Workshop RHEOLOGISCHE 17. Kolloquium und Workshop RHEOLOGISCHE MESSUNGEN AN MINERALISCHEN BAUSTOFFEN,MESSUNGEN AN MINERALISCHEN BAUSTOFFEN,

12. UND 13.03.200812. UND 13.03.2008

The flow SCC of 600 millimeters diameter included 3,2 % of air, and the flow of SCC with 720 millimeters diameter, included 4% of air.

Laboratory research shows that SCC with SP PC, (1,0 w.c. was air-entrained even if % ) the air-

entraining admixture was not usedwas not used

As we can see rheological properties of SCC are very important to obtain prospective air-entrainment of SCC

In next step of laboratory research air-entraining admixture was inserted into the same SCC composition. It caused

bigger air-entrainment of SCC in proportion to dosage of air-entraining

admixture. So, and in this case rheological

properties influenced air-entrainment of SCC.

Air volume in concrete decrease of concrete compressive strength

41

35

28

21

14

7

475 416 357 279 238 178 119

Average 28-

day compressive strength

(Mpa

)

Cement content (kg/m3)

0% air

4% air

8% air

Constantslump

So, how can we decrease unnecessary air-

entrainment of SCC ?

Too low value of rheological parameters -coalescence of air bubbles

Too high value of Too high value of rheological parameters - rheological parameters - disappearingdisappearing of pore that are less than 0,10 mm in diameter

Too low value of rheological parameters - floating of large air

bubbles

Influence of rheological properties of SCC on Influence of rheological properties of SCC on air bubblesair bubbles

How rheological properties of SCC shaping air-

entrainment?

Proposition 1.

Adjusting rheological

properties of SCC

In this case we must use VMA

Agdpz 0

segregation

Outflow qualification of of air bubble:

diameter of air bubbles shape index of air bubbles

Laboratory research showded that SCC was not air-entrained when diameter flow was maximized

until segregation did not occure

Conclusion: SCC with SP incorporate not too much air bubbles when value of yield stress yield stress τ( 0 of )

scc is not too high.

z

pz gdv

18

)(2

Moreover, value of cement paste viscosity ( must be low to)obtain high outflow speed of air bubble

SP [% w.c.]

0

500

1500

2500

3500vi

scos

ity [

mP

a s]

0 0,2 0,4 0,6 0,8

-NSLSP34S34

Influence of SP type and value dosage on concrete mix viscosity

If we know the value of cement paste viscosity and yield stress we can

shape them using type and dosage superplasticizer to achieve adequate air-entrainment

Superplasticizer type and its air-entraining effect

0

20

40

60

80

100

water destiled water water+AEA (0,2% m-c) water+SP (1,0% m-c) water+SP (1,0% m-c) +AEA (1,0% m-c)

surface tension !0-3

Nm t=20,7 oC

SuperplasticizerLignosulfian

LS

Sulfonated Naphtalene

Formaldehyde Condensate

SNF

Sulfonated Melanine

Formaldehyde Condensate

SMF

New Generation Superplasticizers

PolyCarboxylatePolyoxyethylene

PCP

Amino Phosphonate

Polyoxyethylene

AAP

Air-entraining effect + ++ ++ +++ ++

SP decrease value of surface tension

Air-entraining effect of SP is caused i.a. by its

influence on surface tension of water

Proposition 2.Using superplasticizers with

non air-entraining affectAs we can see, the superplasticizer type influences its air-entraining effect, especially PolyCaroxylate superplasticizers type.

Superplasticizers decrease the value of surface tension as much as the air-entraining admixture.

Rapid change of surface tension over a relatively small concentration range

cRT

dc

d si

80

60

40

20

0-4 -3 -2 -1 0 1

Surface tension mN/m()

Surfactant concentration mol/l( )

The rate of surface tension decreases by usage surface active compounds is followed in accordance with Gibbs equation:

Surface tension

Foam

production

Concentration

(b)

where:d – change of surface tensiondc – change of given substance concentration in the solution,Ґs

i – surface concentration (mol/m2),

c – constituent concentration,R – gas constant,T – temperature.

Rapid change of surface tension and foam production over a concentration range

the forces pointing to the left are due to the surface tension. The forces pointing perpendicular to the hemispherical surface are due the air pressure inside the

bubble

(a) Spherical air bubble (b) free-body diagram for right-half of air bubble

Forcesdue to surface tension

Forces due to inside air pressure

Projected area = pR2

R

Pi

Po

In the picture we can see, how air bubble is formated by the surface tension

pres

su

re

ins

ide

an

air

bu

bb

le,

P i

Po

radius, R

RPi

Po

The inner and outer pressures on the spherical air bubble ale Pi and Po, respectively

Pi – Po = 2g /R - Laplace’s law

The size of air bubbles depend on inner and outer pressures

Infuence of naphthalene β-NS , refined lignin sulfonate LS i ( ) ( )polycarboxylate P34, S34 superplasticizer on porosity ( )

structure of 28 days( )

0

20

40

60

80

0,5 % LS

0,45 % NS 0,15 % P340,13 % S34

d > 0,1 md < 0,1 m

Por

e vo

lum

e m

m3 /

cm3

What we do know about the influence of

superplasticizers type on the size of air bubbles ?

PolyCarboxylate superplasticizers decrease the volume of pore diameter more than other superplasticizer

0

20

40

60

80

0,5 % LS 0,45 % NS 0,15 % P34 0,13 % S34

d > 0,1 md < 0,1 m

Por

e vo

lum

e m

m3 /

cm3

But volume of pore with d 0,1 > m increase after 91 days …So, according this research all type of SP cause air-entraining of SCC

0

4

8

12

16

0 0,45 0,55w/c

Ent

rain

ing

[%

]

0,3% 0,5% 0,8%

LS, OPC

05

10

1520

0,35 0,45 0,55w/c

Ent

rain

ing

[%

]

OPC LAC WC25

0,4 0,5 0,6

0

4

8

12

0,35 0,45 0,55w/c

Ent

rain

ing

[%

]

0,3% 0,5% 0,8%

16

0,4 0,5 0,6

LS, LAC

0

4

8

12

0,35 0,45 0,55w/c

Ent

rain

ing

[%

]

0,3% 0,5% 0,8%

16

0,4 0,5 0,6

LS, WC

Portland cement (OPC), Low alkali cement (LAC), and white cement (WC)

Lignosulfonic acid (LS),

Superplasticizers air-entraining problem is more important when proportion w/c of SCC is low (e.g. in case of high performance

SCC)

when the w/c proportion of SCC is low – air-entrainment of SCC is high

Anti-foaming agents:

e.g. Polyoxy Ethylene/propylene ether mixture

can damage air bubbles

Some type of anti-foaming agents: are compatible with Polycarboxylate type superplasticizer and most air-entraining agent, especially with Vinsol type air-entraining agent.

Better performance of SCCProposition 3.

Using Anti-foaming agents

It causes:

-7,5

-10

-12,5

-15

-17,50 0,2 0,4 0,6 0,8

Zeta potencjal

[mV]

SP [% w.c.]

PCPS- sodiumpolycarbonate-polysulfonate

PNS – sodiumpolynapthalenesulfonate

cement

Lon diffusion layer containing zeta potentialDispersion rate

of particles depends on modification effect surface layer of particles by type SP

Modification zeta potential of particles owing to different type SP

Dispersion of air bubbes and cement particions and aggregate

We should use this SP type which can change

surface layer of particles to not

permit air bubbles connect with particles

Proposition 4.Modification of particles electrical potential

It cause:

ConclusionsConclusions

Laboratory research is still continued and its results will show which of this method is

most effective

How can How can we we decrease air-entraindecrease air-entrainment ment of SCC?of SCC?1 Adjusting )1 Adjusting ) thethe rheological properties of rheological properties of SCCSCC:: SCC with SPSCC with SP do not do not incorporate not to much incorporate not to much

air bubbles when value of yield stress τ(air bubbles when value of yield stress τ( 00 of ) of ) scc is not high scc is not high,, Value of viscosity μ ( )Value of viscosity μ ( ) should not be should not be high high to to increaseincrease the outflow of air bubbles speedthe outflow of air bubbles speed2 )2 ) Using Using superplasticizers with non air-superplasticizers with non air-

entraining affectentraining affect..3 Using anti-foaming agents to eliminate air)3 Using anti-foaming agents to eliminate air) bubblesbubbles..4 )4 ) MModification of odification of electric electric particles potential to particles potential to help help air bubbles outflowair bubbles outflow