2nd CRM
The Immobilization of Radioactively Contaminated Soil in Cementitious Materials
Shuxin Bai, Shengliang YangNational University of Defense Techn
ology, P.R.China
2nd CRM
Introduction/Background In China, a mass of radioactively
contaminated soil is required to be disposed.
From the point of effectiveness and economy, cementation is a promising candidate approach to immobilize such kind of waste.
2nd CRM
Introduction/Background Soil in the cement paste may deteriorate
its allover properties. Especially when soil is present in the form
of clump. But if well designed and processed, the
contaminated soil can be mixed with cement and additional agents to form clay cement concrete of good durability.
2nd CRM
Research Methodology The physical and chemical processes occurring du
ring the harden process of soil cement system including: the cementation of cement, soil and other ag
ents, and role of them, interactions of cement and soil, the state of radionuclides in the concrete, etc.
Specific of cementation process for soil: pretreatment of the soil, mixing device and method, pos
t-treatment of the cementation product.
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Research Methodology The influence of cementitious materials and proce
sses on properties of concrete such as strength, microstructure, porosity, cracking etc.
The degradation of the soil cement concrete in water at different conditions including: water penetration and transport in pores of th
e concrete, dissolution of different components (C-S-H, clay .etc) in the concrete block, the leaching and retention behaviors of different radionuclides (actinides specially).
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Research Methodology
Wasterform Preparing
Aging for 28d
Cementing Materials
Pretreating of Soil
Testing Properties
XRD
SEM+EDS
Thermal Cycling
Leaching Behavior
Shocking Properties
Compressive Strength
Other aspects
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Experimental Techniques and Equipment
Techniques and Equipment XRD: D-Advance, Germany SEM-EDS: S-4800 SEM, HORIBA EDS ICP-AES: IRIS Advantage1000, USA Universal Materials Testing Machine Mixing Device
Materials various cements, cement additives, contaminated soil
samples.
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Research Approach and Results Different types of cement was adopted to immobilize the co
ntaminated soil. Ordinary Portland Cement (OPC) is used as the main composition.
Additives such as super-plasticizers, pulverized fly ash (PFA), zeolite, silica fume etc. was introduced to enhance the cement properties.
Substituent elements for radionuclides were added to the soil samples
Cs+, Sr2+, Ce3+ were added to substitute the 137Cs, 90Sr and 239Pu concentration of each element: ~0.01%(wt)
A — CaCO3
B — SiO2
C — CaSO4·2H2O
D —CaAl2Si2O8
oxides SiO2 CaO SO3 Al2O3 Fe2O3 K2O MgO Na2O
wt(%) 40.3 26.5 13.5 9.43 4.49 2.78 1.91 1.05
Size(mesh) <5 5~20 20~40 40~120 >120
wt(%) 17.9 41.9 6.40 22.2 11.6
soil
Sample group
Cement:Soil
PFA(%) SF(%) Zeolite(%) c/w plasticizer(%)A1 1:2.0 15 5 0 0.40 0.5A2 1:2.0 15 10 0 0.45 0.5A3 1:2.0 15 15 0 0.50 0.5B1 1:2.0 15 0 5 0.50 0.5B2 1:2.0 15 0 10 0.50 0.5B3 1:2.0 15 0 15 0.50 0.5C1 1:1.5 15 10 10 0.50 0.5C2 1:2.0 15 10 10 0.50 0.5C3 1:2.5 15 10 10 0.55 0.5C4 1:3.0 15 10 10 0.60 0.5D1 1:2.0 0 0 10 0.50 0.5E1 1:2.0 15 0 10 0.50 0.0
As fabricated wasteform samplesaged wasteform samples
no vibration
Cross-section
4416cm
55cm
Cemented samples Good compatibility High soil volume
(2.0~2.5:1, or 67~70%wt) Density, but pores visible
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Research Approach and Results The compressive strength of each group show good results.
0
10
20
30
40
50
60
70
A1 A2 A3 B1 B2 B3 C1 C2 C3 C4 D1 E1sampl e
comp
ress
str
engt
h /M
Pa
Aged 28d
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Leaching rate results
0
0.2
0.4
0.6
0.8
1
1.2
A1 A2 A3 B1 B2 B3 C1 C2 C3 C4 D1 E1
sample
leac
hing
rate
(X10
-3 cm
/d)
Cs+
Sr2+Ce3+
137 3Cs 4 10 cm / d 90 3Sr 1 10 cm / d 239 5Pu 1 10 cm / d
GB7023-86Standard:
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Research Approach and Results
Free water check: no free water observed after aged 7d Thermal cycle durability:
Loss of compressive strength (-25~15C, 5cycles): <25%
No obvious change after 60 cycles (-40C ~ 40C, quenching in LN2)
No. Before/MPa
After/MPa
Loss %
A3 27.5 25.3 8.0
B3 30.0 25.7 11.2
C3 24.8 19.7 20.4 60 cycles from -40C to 40C
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Influence of additives on the cement hydraulic process
Influence of soil Influence of PFA Influence of silica fume Influence of zeolite
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Influence of soil
XRD of hydrated cement and cement-soil grout aged 21d
Pure OPC cement
Cement+soil (1:1)
AFm decreased for the exist of CaSO42H2O in the soil prevents the formation of AFm from AFt.
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Influence of PFA
XRD of samples aged for 21d XRD of samples aged for 60d
No obvious difference for 21d samples, however for 60d samples phase C remains little amount, indicates reaction between cement and PFA at later period of setting
cement
Cement +PFA
cement
Cement +PFA
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Influence of PFA
0. 1320
0. 3719
0. 54690. 4767
0. 0000
0. 1000
0. 2000
0. 3000
0. 4000
0. 5000
0. 6000
Sr Ce
leac
hing
rat
e(X1
0-3cm
/d) 15%PFA
0%PFA
The adding of PFA improves leaching properties:
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Influence of silica fume
cement
Cement +SF Active SiO2 reacts with Ca(OH)2
to form C-S-H
SiO2 + Ca(OH)2 = CaSiO3 + H2O
CaSiO3 + nH2O = CaSiO3·nH2O
XRD of samples aged for 21d
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0
1020
3040
5060
70
0 2 4 6 8 10 12 14 16SF %( )
stre
ngth
MPa
()
0. 0000
0. 1000
0. 2000
0. 3000
0. 4000
0. 5000
0. 6000
0% 5% 10% 15% 20%SF
leac
hing
rat
e(X1
0-3cm
/d)
SrCe
Influence of silica fume
The adding of SF increases the compressive strength of waste forms
The adding of suitable amount of SF decreases the leaching rate of waste forms
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Influence of zeoliteA — SiO2
B — montolite
0. 000. 100. 200. 300. 400. 500. 600. 700. 800. 901. 00
0% 5% 10% 15% 20%zeol i te
lea
chin
g ra
te(X
10-3
cm/d
)
SrCe The leaching rate decrea
ses with the adding of zeolite
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Influence of other aspects water/cement ratio: plasticizer is necessary Vibration of cemented waste form before setting increase t
he strength and decrease the leaching rate
0. 13200. 2357
0. 3719
0. 9249
0. 000. 100. 200. 300. 400. 500. 600. 700. 800. 901. 00
0. 50 0. 55w/ c
leac
hing
rat
e (X
10-3
cm/d
)
Sr2+Ce3+
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Research results and conclusion
cemented waste forms with high durability and low cost: Soil/cement ratio: 2.0~2.5 Compressive strength: >10MPa Leaching rate of Cs+, Sr2+ <410-3, 110-3 cm/d Thermal cycle durability: the same after 60 freeze
thaw cycles (-40,+40 )℃ Unit cost of immobilization: <50€/t of soil
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Research results and conclusion
the soil cemented in this work which is mainly composed of sand and stone has good compatibility with cement and a high encapsulating ratio can be achieved.
At a ratio of cement/soil =1:2.5 the cementing process is still viable and the properties of the waste form including the strength and leaching rate of Sr2+ and Cs+ are accordant with the requirement of the standards .
The investigation of the hydraulic process of the cemented specimen indicates that the exist of soil has apparent effect on the hydraulic process. The CaSO44H2O in the soil retards the formation of hydraulic product AFm .
2nd CRM
Research results and conclusion The effects of the addition of silica fume, zeolite and PFA on the properties
of the cemented waste forms were studied and the results show that the addition of these additives can improve the properties of the waste forms including enhancing the strength and reducing the leaching rate.
Some other cementation processing aspects such as water/cement ratio and whether the specimen being vibrated or not also have important effects on the properties of the waste form. The water/cement ratio can be reduced by adding super-plasticizer to improve the anti-leaching behavior. The vibration during the cementation process can raise the strength and reduce the leaching rate.
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Further works
Massive waste form process of soil immobilization
Suitable method to test the leaching of 239Pu Leaching behavior and immobilizing
mechanism
2nd CRM