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Comparative Study Using Some Advanced Simulation Methods for Leaching of Cementitious Materials Over Ten Thousands of Years
- T. Torichigai*, K. Yokozeki*, T. Ishida**,
- K. Nakarai***, D. Sugiyama****
* KAJIMA corporation (JAPAN) ** The university of Tokyo *** Gunma university **** Central Research Institute of Electric Power Industry
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Background(1/3)
Nuclear power generation covers 30 percents of power generation in Japan. Method for disposing radioactive waste is very important.
RADIOACTIVE WASTE ・Concrete Pit （-10～-5m） ・Sub-surface Disposal (-100～-50m) ○Low-level radioactive waste →Geological disposal (~-300m) ○High-level radioactive waste Underground (-100～-50m)
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Background(2/3)
Cross sectional view of sub-surface disposal repository Concrete pit：Maintaining stability of the repository Mortar：Preventing radioactive nuclides to leak Bentonite：Preventing underground water to permeate to the repository
Low diffusion layer (Mortar) Tunnel Low permeability layer (Bentonite) Reinforced concrete pit Backfill （Concrete or Soil) Waste packages
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*Calcium leaching to underground water *Chemical reaction between mortar and bentonite
Mortar Bentonite Concrete Ca2+ Ca2+ Ca2+ Ca2+
Long-term durability (over 10,000 years) is demanded for this repository Issues for cementitious material *Crack *Chemical degradation Evaluating long-term durability of concrete is necessary
Background(3/3)
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Target of this study
Simulation-code for evaluating calcium leaching DuCOM, LIFE D.N.A., CCT-P
for example… ※Method of simulation is different.
Evaluating calcium leaching of cement hydrates by 3 codes.
- What kind of deterioration will occur in
sub-surface disposal repository?
- How fast is the deterioration speed?
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Evaluating method for calcium leaching
Thermodynamic database Solid-liquid equilibrium for calcium Advection Diffusion Electrical potential
& L=a x t1/n
Mass Transfer Dissolution/Precipitation of Hydrates
Numerical Simulations Experimental Models n ; parameter (generally n=2) a ; constant parameter
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Comparison of 3 codes
Chemical reactions Code Model of diffusion coefficient Cementitious material Bentonite DuCOM * Solid/liquid equilibrium for calcium Absorption of Ca ions LIFE D.N.A. * Solid/liquid equilibrium for calcium (considering with Na, K) * precipitation of CaCO3,Mg(OH)2， Friedel’s salt. Absorption of Ca ions CCT-P * Thermodynamic database * Incongruent dissolution of C-S-H * Dissolution/ precipitation of CaCO3 Ion exchange reactions of Na, K, Ca and Mg
( )
i i eff
D f D ⋅ ⋅ ⋅ = φ β η
ion eff
D S D ・ ・ ・ δ φ Ω =
n
t D t D ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = ) ( ) ( ) ( ) ( φ φ ・
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Simulation model
3.0m 1.0m 1.0m 6.0m Rock Concrete Bento- nite Mortar 2E-9 6.6E-13 2.8E-10 3.3E-13
Boundary line (constant)
Ca2+ Na+ K+ Mg2+ SO4
2-
Cl- CO3
2-
pH 0.13 0.77 0.03 0.16 0.14 0.44 0.62 8.6
Composition of underground water
(mmol/l)
Diffusion coefficient(m2/s) migration of Calcium ion
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Conditions
DuCOM ; Portlandite, C-S-H LIFE D.N.A. ; Portrandite, C-S-H, Calcite, Brucite, Friedel’s salt, NaOH, KOH CCT-P ; All hydrates in database
Unit Quantity (kg/m3) W LPC FA LSP S G Concrete Mortar 45 2.5 160 249 107 249 832 786 45 2.5 230 358 153 307 1223
（%） Air (％)
Mix proportions of concrete and mortar Cement hydrates using in calculation
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20 40 60 80 100 2.5 3.0 3.5 4.0 4.5 Distance from boundary line（ m） Calcium leaching rate（ ％） DuCOM LIFE D.N.A. CCT- P
Simulation result of calcium leaching rate at 50,000 years
Leaching depth：DuCOM＞LIFE D.N.A.＞CCT-P
Concrete Bentonite Rock
Leaching depth：DuCOM＞ CCT-P ＞ LIFE D.N.A. Faced to Rock Faced to Bentonite Precipitations
Leaching depth
decrease of diffusion coefficient
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Evaluating for calcium leaching speed
Calcium leaching speed of concrete (faced to rock)
100 200 300 400 500 600 50 100 150 200 250 time（ √ year） leaching depth(mm) DuCOM LIFE D.N.A. CCT- P
Leaching speed：DuCOM＞LIFE D.N.A.＞CCT-P
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Evaluating for calcium leaching speed
Calcium leaching speed of concrete (faced to rock & bentonite)
100 200 300 400 500 600 50 100 150 200 250 time（ √ year） leaching depth(mm) DuCOM LIFE D.N.A. CCT- P 100 200 300 400 500 600 50 100 150 200 250 time（ √ year） leaching depth(mm) DuCOM LIFE D.N.A. CCT- P
Na+，K+ from Bentonite control Calcium leaching from concrete
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Degradation process of cement hydrates
D increase Rock D increase Rock D decrease D increase Bento nite D increase D increase CSH leaching Precipitate(Calcite) CH leaching Precipitate (Calcite, Brucite, Friedel’s salt ) Rock
DuCOM LIFE D.N.A. CCT-P
Bento nite Na+, K+ D;diffusion coefficient Concrete D increase Bento nite Concrete
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Changing in diffusion coefficient
Dissolution/precipitation of cement hydrates
( )
i i eff
D f D ⋅ ⋅ ⋅ = φ β η
ion eff
D S D ・ ・ ・ δ φ Ω =
n
t D t D ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = ) ( ) ( ) ( ) ( φ φ ・
... Porosity increase/decrease ... Diffusion coefficient increase/decrease
1E- 13 1E- 12 1E- 11 1E- 10 25 50 75 100 Calcium leaching rate(% ) Diffusion coefficient(m
2/ s)
DuCOM LIFE D.N.A. CCT- P
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Influential factor for Calcium leaching
- Changing in diffusion coefficient
- Chemical reaction (especially, precipitation)
- Degradation process of cement hydrate is different
- Calcium leaching speed is different
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Conclusions
- What kind of deterioration will occur in sub-surface
disposal repository?
Portlandite & C-S-H leach from cementitious material Secondary minerals would precipitate Degradation process is different in 3 codes
- How fast is the deterioration speed?
Calcium leaching speed is DuCOM > LIFE D.N.A.>CCT-P Calcium leaching depth at 50,000 years are 130~500mm The reason why simulation result is different… Changing in diffusion coefficient Chemical reaction (especially, precipitation)
Evaluating calcium leaching of cement hydrates by 3 codes.
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Appendix
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DuCOM
ion eff
D S D ・ ・ ・ δ φ Ω =
Calcium liquid/Solid equilibrium Transport by solution flow Transport by diffusion Mass Transfer Dissolution/Precipitation of Hydrates Calcium leaching = Porosity increase = D increase
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LIFE D.N.A.
( )
i i eff
D f D ⋅ ⋅ ⋅ = φ β η
Transition zone ions
Calcium liquid/Solid equilibrium Transport by solution flow Transport by diffusion Electric force Mass Transfer Dissolution/Precipitation of Hydrates
CP0Ca Cp1Ca=ACp1･CP0Ca
CP2Ca
C0Ca C1Ca Ca(OH)2 C- S- H
Ca2+ Concentration in liquid ① ② ③
n Ca Ca cp Ca p pCa
C C A C C
/ 1 1
⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = ･
Ca2+ Concentration in Solid
( )
0.18)
0.18)
0.07 0.001
2
φ φ φ φ ・ + = f
vol vol vol
P S d G c ⋅ ⋅ − ⋅ − = 1 1 β
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Transport by solution flow Transport by diffusion
CCT-P
n
t D t D ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = ) ( ) ( ) ( ) ( φ φ ・ ⎭ ⎬ ⎫ ⎩ ⎨ ⎧ + − + + − + + + + + − + =
− − − 2 2 1 2 1 1 1
) 1 1 ( 1 1 ) 1 ( ) 1 log( 1 log 1 log x x A x x A A x x x x x x K x x K
i i i i i i i i
logKsp of C-S-H gel depend on the rate of Ca/Si
the thermodynamic database (Chemical reaction code HARPHRQ) Incongruent dissolution of C-S-H Mass Transfer Dissolution/Precipitation of Hydrates
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10 20 30 40 50 60 20 40 60 80 100 120 Time (years) Ca leaching depth (mm) Lagerblad(2001) Yokozeki(2002) Saito et al.(2003) ： Y=2.42√ t Leaching depth at 50,000years=541mm The most deteriorated data Average of all data ： Y=0.94√ t Leaching depth at 50,000years=210mm
Investigation result of the old structures
Simulation results = 130～500mm at 50,000 years
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0.0 0.2 0.4 0.6 0.8 1.0 5 10 15 20 25 Ca concentration in liquid（ mmol/ l） rate of Ca concentration in solid/ initial OPC Model(OPC) LPCFA Model(LPCFA)
Comparison DuCOM to LIFE D.N.A.
CP0Ca C0Ca C1Ca Ca(OH)2 C- S- H
Ca2+ Concentration in liquid ① ② ③ Ca2+ Concentration in Solid
C0Ca
① ②
LIFE DNA (model change)
42.5 97.5 200 50 100 150 200 250 LIFE D.N.A. LIFE D.N.A. (Model change) DuCOM Leaching depth(mm) 1,000year 10,000year
<Different type of cement> <affect Na ions & K ions>
DuCOM
