Characterisation and reduction by nano-additions of the effect of …mmsconferencing.com/nanoc/presentations/igorcampillo.pdf · 2008-06-13 · NANOC ® CENTRO DE APLICACIONES DE

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Characterisation and reductionby nano-additions of theeffect of Ca-leaching in cement pastes

J.J. Gaitero, Y. Saez De Ibarra, E. Erkizia, I. Campillo

Unidad AsociadaNANOC®

CENTRO DE APLICACIONESDE NANOMATERIALESEN CONSTRUCCION

* Ca-leaching

Calcium leaching is an ubiquitous process wherever concrete is in contact with water

Normal paste Ca-leached paste



* Ca-leaching

Calcium leaching of cementitious materials is controlled by the chemical equilibrium of the calcium-silicate-water system

Equilibrium zone for portlandite[Ca++]>20 mol/m3

Equilibrium zone for CSH2 mol/m3 <[Ca++]<20 mol/m3

Silicon rich gels: end product of Ca-leaching[Ca++]<2 mol/m30

0.5

1

1.5

2

2.5

3

0 5 10 15 20 25

C/S

Ca++ mol/m3

Berner leaching curve

U.R. Berner, Radiochimica acta, 44/45, 387-393 (1988)

Ca-leaching

C/S

Ca++ (mol/m3)



* Ca-leaching

Leaching effects in the C-S-H matrix

As leaching goes on, the average C/S-ratio in CSH is reduced

The decrease in the C/S-ratio is accompanied by a Si polymerisation

By nanoindentation, Ca leaching has been associated with α-CSH

from accelerated leaching tests:

•E(α-CSH) goes from 21,7 to 3,0 GPa•E(β-CSH) goes from 29.4 to 12 GPa

G. Constantinides, F.J. Ulm, MIT



* Silica addition

Ca(OH)2 + SiO2 → C-S-H (1)

C-S-H(1) + SiO2 → C-S-H (2)C/S (1) > C/S (2)

Higher EfficiencyMORE GEL

Silica has been usually added in the formof Silica Fume (100-1000 nm)

What happens if we add lower sized silica (nanosilica)?



* Objectives

To do a systematic study of the phenomenon of calcium leaching in cement pastes

To study the influence of nanosilica additions in the calcium leaching process

To estimate the validity of this addition as a mean of controlling calcium leaching



* Experimental

Our experiments have executed over three kind of samples:

•Plain cement paste with w/c=0.5 •Cement paste + colloidal silica (1.8% )(15 nm particle size).•Cement paste + agglomerated dry silica (6%)(~1 µm grain size)

They have been cured in a saturated solution of Ca(OH)2 for 28 days.

After that, they have been introduced in a 6M solution of ammonium nitrate (NH4NO3)

Samples have been tested at 0, 10, 20, 40 and 60 days



* Experimental



* ExperimentalExperimental techniques for this work• X-ray difractometry (XRD), to follow the crystalline phases evolution, and in particular that of portlandite, and the portlandite consumption rate by the nanosilica addition.

• 29Si NMR, to follow the Si chain growth and redistribution by the addition of nanosilica.

• EDX-Microanalysis, to follow the Ca/Si ratio over time.

• ESEM, to picture the cement paste at different stages of Ca leaching

• Hg Porosimetry, to follow the porosity of the paste



* Results X-Ray

O- Days

Position [°2Theta]

10 20 30 40 50 60 70

Counts

0

50

100

150

0

50

100

150

0

50

100

150

0DIAS-comp1.CAF

L1-0DIAS_smth.XRDML

N1-0DIAS_smth.XRDML

Position [°2Theta]

10 20 30 40 50 60 70

Counts

0

20

40

60

80

0

20

40

60

80

0

20

40

60

10DIAS-comp1.CAF

L1-9DIAS_smth.XRDML

N1-9DIAS_smth.XRDML

10 days

Portlandite has been consumed ~ 10 days

Plain cementPlain cement

Colloidal silica

Dry silica Dry silica

Colloidal silica



10

20

30

40

50

60

-10 0 10 20 30 40 50 60 70

POROSITY

CPCSADS

Por

osity

(%)

Leaching time (days)

< 10 days: Portlandite consumption > 10 days: no big changes in porosity

* Results Hg-porosity

Colloidal silica

Plain cement paste

Agglomerated dry silica



* Results ESEM

O- Days 10 days

Dissolution frontNo Ca-leaching



0

0.5

1

1.5

2

2.5

-10 0 10 20 30 40 50 60

Ca/Si

CPCSADS

C/S

Leaching time (days)

* Results EDX-microanalysis

Colloidal silica

Plain cement paste

Agglomerated dry silica

C/S decreases as leaching evolvesMore moderate for nanosilica modified cement pastes



* Results 29Si NMR

Qn

Tetrahedrallycoordinated Si atom

Number of bridging oxygens per tetrahedron

Connectivity Chemical Shift (δ, ppm)Q0 -66 to -74Q1 -77 to -82Q2 -85 to -89Q3 -92 to -100Q4 -103 to -115

29Si Chemical Shifts for Different Structure Units of Silicate Species

OH

SiOHHO

HO

Q0

OH

SiOHO

HO

O

Si

Q3

O

HO OH

SiOHOH

Si

OH

HOHO

OH

SiOHO

HO

OH

SiO

HO O

SiOO

Si

SiOHHO

OH

Si

HO

HO

HOOH

OH

HO

Q4

O

SiOHO

HO

OH

SiOHOH

Si

OH

HOHO

Q2 Q1



* Results 29Si NMR

(ppm)-115-110-105-100-95-90-85-80-75-70-65-60

B3-0days

Portland cement with differnet Ca leaching times

(ppm)-115-110-105-100-95-90-85-80-75-70-65-60

B2-12days

(ppm)-115-110-105-100-95-90-85-80-75-70-65-60

B2-20days

(ppm)-115-110-105-100-95-90-85-80-75-70-65-60

B2-40days

(ppm)-115-110-105-100-95-90-85-80-75-70-65-60

B2-60days

Non-degraded

Q0

Q1 Q2

Q3

Degraded

NMR spectra evolution (plain cement paste)



* Results 29Si NMR

Colloidal silicaDry silica

(ppm)-115-110-105-100-95-90-85-80-75-70-65-60

Portland cement with different additionsat 40 days of Ca leaching

B2-40days

(ppm)-115-110-105-100-95-90-85-80-75-70-65-60

L1-40days

(ppm)-115-110-105-100-95-90-85-80-75-70-65-60

N1-40days

Effect of the nanosilica additions at 40 days

Plain Cement

Q0

Q1

Q2

Q3



Time (days)

* Results 29Si NMR

Rela

tive

inte

nsit

yQ

3

Evolution of Q3 over time

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70

Plain cement paste

Colloidal silica

Dry silica



Relative Intensity of Q3 to Q2

Less Ca leaching

* Results 29Si NMR

Rela

tive

inte

nsit

yQ

3/

Q2

Time (days)

0

0.5

1

1.5

2

2.5

3

3.5

4

0 10 20 30 40 50 60 70

Plain cement paste

Colloidal silica

Dry silica



* Conclusions

A coherent set of data from different characterisation techniques has been obtained, confirming that:• Portlandite consumption occurs in the early stage of accelerated

Ca leaching

• Pozzolanic reaction induced by dry silica prevents early Ca leaching

• Si polymerisation induced by Ca leaching in nanosilica modified cement pastes is less intense than in blank cement pastes

• Nanosilica addition to cement-based materials can control C-S-Hdegradation induced by Ca leaching



* AcknowledgementsThe NANOC Team

StaffDr Antonio PorroDr Igor Campillo

Dr Yolanda de MiguelDr Edurne Erkizia

Dr José Antonio IbáñezDr. María Moragues

Dr Jorge Sánchez Dolado

StudentsJuan José Gaitero

Yolanda Saez De IbarraItsaso Berra

Hegoi ManzanoAinara Montero

TechniciansEneritz Belasko

Raquel Vega

Funding:Basque Governmentunder the ETORTEK, SAIOTEKand BIZKAITEK programs



THANK YOU VE

RYMUCH

FOR YOUR ATTENTIO

N !!

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Characterisation and reduction by nano-additions of the effect of …mmsconferencing.com/nanoc/presentations/igorcampillo.pdf · 2008-06-13 · NANOC ® CENTRO DE APLICACIONES DE