Internal Chloride Binding of OPC Pastes: Modelling Using Binding - - PowerPoint PPT Presentation

Internal Chloride Binding of OPC Pastes: Modelling Using Binding Isotherms

• Dr. Dipl. Eng. M.V.A. (Miruna) Florea

L.C. (Lara) Quaas, MSc

• Prof. dr. ir. H.J.H. (Jos) Brouwers

Sustainable energy in the Netherlands

2 4 6 8 10 1990 1995 2000 2005 2010* Energy production (%) Year Other biomass combustion Co‐firing biomass in power plants Municipal solid waste incineration Solar power Biogas Wind energy Hydropower

• Biomass fly ashes
• MSWI by-products

Environmental legislation

Contaminant Shaped building materials (mg/m2) Non-shaped building materials (mg/kg) IBC materials (mg/kg) Sb 8.7 0.32 0.7 As 260 0.9 2 Ba 1500 22 100 Cd 3.8 0.04 0.06 Cr 120 0.63 7 Co 60 0.54 2.4 Cu 98 0.9 10 Hg 1.5 0.02 0.08 Pb 81 2.3 2.1 Mo 144 1 15 Ni 400 0.44 8.3 Se 4.8 0.15 3 Sn 50 0.4 2.3 V 320 1.8 20 Zn 800 4.5 14 Br- 670 20 34 Cl- 110000 616 8800 F- 2500 55 1500 SO4

2-

165000 1730 20000

MSWI by-product leaching

• By-products often exceed the leaching limits of the Dutch

environmental legislation for more than one contaminant (mostly heavy metals and anions)

• Contaminants can be bound in cement-based mixtures
• Chloride leaching is one of the largest challenges
• It is often challenging to identify the source of chlorides in

the by-products

SCOPE

• To study the individual chloride binding capacity
• f cement pastes, using various parameters

Chloride binding in cement pastes

• Internal chloride binding experiments
• Cement type: CEM I 42.5N from ENCI; w/b=0.5
• Chloride type: NaCl, CaCl2, SbCl3, CuCl2
• Chloride concentrations: 0, 1, 3 and 5%
• Static leaching with daily stirring, up to 42 days

Chloride leaching

2000 4000 6000 8000 10000 12000 Ref. 1% NaCl 3% NaCl 5% NaCl 1 d 5 d 14 d 21 d 28 d 35 d 42 d

Leached Cl‐ (mg/L) Added salt

2000 4000 6000 8000 10000 12000 Ref. 1% CaCl₂ 3% CaCl₂ 5% CaCl₂ 1 d 5 d 14 d 21 d 28 d 35 d 42 d

Leached Cl‐ (mg/L)

Chloride leaching

2000 4000 6000 8000 10000 12000 Ref. 1% SbCl₃ 3% SbCl₃ 5% SbCl₃ 1 d 5 d 14 d 21 d 28 d 35 d 42 d

Leached Cl‐ (mg/L) Added salt

2000 4000 6000 8000 10000 12000 Ref. 1% CuCl₂ 3% CuCl₂ 5% CuCl₂ 1 d 5 d 14 d 21 d 28 d 35 d 42 d

Leached Cl‐ (mg/L)

mAFm

…

mCSH mCH mb mhp mw mb mw

The Paste Model

H.J.H. Brouwers, Cem. Concr. Res 34, 1697-1716, 2004 H.J.H. Brouwers, Cem. Concr. Res 35, 1922-1936, 2005

The binding capacity

• f a cement paste is

a function of:

• type and ammount of

hydration product

• ion concentration in

the pore solution

• age and porosity of

the sample

b b, CSH b, AFm

C C C  

Hydration reactions: OPC

3 1.7 3.2

C S+4.5H C SH +1.3CH 

2 1.7 3.2

C S+3.5H C SH +0.3CH 

3 4 14

C A + CS+14H C ASH 

3 4 22

C A+CH+21H C AH 

3 6 3 36

C A +3CS+36H C AS H 

4 3 6 2 18

C AF+2C S+22H C AFS H +4CH 

4 2 6 2 18

C AF+2C S+20H C AFS H +2CH 

H.J.H. Brouwers, Cem. Concr. Res 34, 1697-1716, 2004 H.J.H. Brouwers, Cem. Concr. Res 35, 1922-1936, 2005

Chloride binding of the AFm phase

• The ion exchange mechanism
• The dissolution and precipitation mechanism

Hydroxy-AFm:

C3A.Ca(OH)2.nH2O

Monocarboaluminate:

C3A.CaCO3.nH2O

Hemicarboaluminate:

C3A .½ CaCO3 .½ Ca(OH)2.nH2O

Friedel salt:

C3A.CaCl2.nH2O

Monosulfoaluminate:

C3A.CaSO4.nH2O

Hemisulfoaluminate:

C3A .½CaSO4.½Ca(OH)2.nH2O

4

b, AFm b, SO AFm b, HO AFm

C C C

 

 

Chloride binding isotherms

2 4 6 8 10 12 0.5 1 1.5 2 2.5 3

HO‐AFm SO4‐AFm AFm

external Cl (mol/l) bound Cl, mg/ g sample

HCP1

U.A. Birnin-Yauri and F.P. Glasser, Cem. Concr. Res., V.28, N.12, p.1713-1723, 1998

• H. Hirao, K.Yamada, H. Takahashi, H. Zibara, Vol.3, No.1, 77-84, 2005

XRD data: reference paste

100 200 300 400 500 600 700 800 900 5 15 25 35 45 55 Intensity [a.u] Position [ᵒTheta]

Etr Etr CH CH CH CaCO₃

XRD data: samples

a) 1% Cl, b) 3% Cl and c) 5% Cl from NaCl a) 1% Cl, b) 3% Cl and c) 5% Cl from CaCl2

XRD data: samples

a) 1% Cl, b) 3% Cl and c) 5% Cl from CuCl2 a) 1% Cl, b) 3% Cl and c) 5% Cl from SbCl3

Model adjustments

• The degree of hydration was adjusted for CaCl2 and CuCl2
• HO- AFm is considered not to form in the presence of Cl-
• NaCl samples leached a lot more sulphates than the others, so the

amount of SO4-AFm in the sample was lowered

• Not enough Cl- were available at lower chloride concentrations (0.28

M) to transform all SO4-AFm into Friedel’s salt.

5 10 15 20 25 30 0,5 1 1,5 2 2,5 3 Bound Cl [mg/ g d.s.] Chloride concentration [M] from NaCl Experimental Cb_external CSH-Z SO₄-AFm HO-AFm

Model adjustments

2 4 6 8 10 12 0,5 1 1,5 2 2,5 3 Bound Cl [mg/ g d.s.] Chloride concentration [M] from NaCl Experimental Cb internal CSH-Z SO₄-AFm

Model results

2 4 6 8 10 12 0,28 0,82 1,33 Bound Cl ‐[mg/ g d.s.] Chloride concentration [M] from NaCl Cb_final Experimental 2 4 6 8 10 12 0,28 0,82 1,33 Bound Cl ‐[mg/ g d.s.] Chloride concentration [M] from CaCl2 Cb_final Experimental

Model results

2 4 6 8 10 12 0,28 0,82 1,33 Bound Cl ‐[mg/ g d.s.] Chloride concentration [M] from SbCl3 Cb_final Experimental 2 4 6 8 10 12 0,28 0,82 1,33 Bound Cl ‐[mg/ g d.s.] Chloride concentration [M] from CuCl2 Cb_final Experimental

Conclusions and further steps

• The OPC paste recipes that contain NaCl leach more chlorides

than the paste recipes that contain other chlorides. This is true for all chloride concentrations.

• Recipes containing SbCl3 result in a high leaching at an early stage

for OPC which decreases over time again.

• When the XRD results of samples containing 1% Cl from CaCl2 and

CuCl2 are compared, it becomes clear that less portlandite is formed in the copper chloride samples. However, C3S peaks are visible due to the fact that there is still unreacted cement.

• A Rietveld refinement will be attempted in order to validate the

model

• An internal chloride binding model was proposed, based on an

external binding model and the XRD results from this study.

• The final chloride binding model correctly predicts the bound

chlorides from the four sources employed.

• The binding of the associated cation will be further investigated and

correlated with the chloride binding.

Questions, thoughts, ideas… Thank you!