- Open Access
Influences of specific ions in groundwater on concrete degradation in subsurface engineered barrier system
© The Author(s) 2016
- Received: 9 December 2015
- Accepted: 2 June 2016
- Published: 16 June 2016
Many disposal concepts currently show that concrete is an effective confinement material used in engineered barrier systems (EBS) at a number of low-level radioactive waste (LLW) disposal sites. Cement-based materials have properties for the encapsulation, isolation, or retardation of a variety of hazardous contaminants. The reactive chemical transport model of HYDROGEOCHEM 5.0 was applied to simulate the effect of hydrogeochemical processes on concrete barrier degradation in an EBS which has been proposed to use in the LLW disposal site in Taiwan. The simulated results indicated that the main processes that are responsible for concrete degradation are the species induced from hydrogen ion, sulfate, and chloride. The EBS with the side ditch drainage system effectively discharges the infiltrated water and lowers the solute concentrations that may induce concrete degradation. The redox processes markedly influence the formations of the degradation materials. The reductive environment in the EBS reduces the formation of ettringite in concrete degradation processes. Moreover, the chemical conditions in the concrete barriers maintain an alkaline condition after 300 years in the proposed LLW repository. This study provides a detailed picture of the long-term evolution of the hydrogeochemical environment in the proposed LLW disposal site in Taiwan.
- Concrete degradation
- Reactive chemical transport
- Engineered barriers system
- Radioactive waste disposal
The engineered barriers system (EBS) is an integral part of the radioactive waste disposal facility. The EBS represents the manmade, engineered materials of a repository, including the waste form, waste canisters, concrete barrier, buffer materials, backfill, and seals, and can be used as physical and/or chemical obstructions to prevent or hinder the migration of radionuclides (Dupray and Laloui 2014; IAEA 2001a). The function of the EBS is to prevent and/or hinder the release of radionuclides from the waste to host rock and biosphere. However, the lack of an appropriate EBS design in the concrete barrier, backfill, and the selection of sealing and covering materials for trenches, vaults, and ditches may result in the ingress of groundwater and the release of radionuclides from the disposed wastes (IAEA 1999, 2001a, b).
Several current disposal concepts indicate that concrete is an effective confinement material that is used in engineered barriers at a number of low-level radioactive waste (LLW) disposal sites in most countries (IAEA 2001a, b). Over the past few decades, a number of studies focused on the assessment of concrete barriers with the properties of encapsulation, isolation, or retardation of a variety of nuclear hazardous contaminants to ensure the reliable long-term performance of such a disposal concept. Jantzen et al. (2010) proposed the use of cements in radioactive and hazardous waste disposal and provided an advanced understanding of cement–waste interactions and the mechanisms in which contaminants are retained. Glasser et al. (2008) discussed cement paste deterioration by detrimental chemical reactions and the mechanisms that manage the transport of ions, moisture, and gas. He also reviewed various chemical degradation phenomena, such as microstructural alterations, that result from exposure to chlorides and carbon dioxide and sulfate attacks from external sources that result in the formation of ettringite and thaumasite. However, a major concern of this EBS design is that concrete may be subject to degradation by re-crystallization and chemical reactions with the aqueous environment. A number of reactions may occur simultaneously in groundwater and cement-based materials, including the dissolution of portlandite that is generated from the intrusion of hydrogen ion, the increase of the concentration of calcium in the pore solution, formation of ettringite by sulfate attacking the cement, and the dissolution of Calcium–Silicate–Hydrate (CSH) gel by chloride entering the cement, and the formation of Friedel’s salt (Luna et al. 2006). Moreover, Bruno et al. (1999) indicated that the interaction of pore water with accessory minerals of bentonite, such as sulfate dissolution-precipitation, and pyrite oxidation, controlled the geochemical characteristics of the system. The repository environment (for example, the pH, Eh, and ionic composition of the surrounding water) affects EBS performance in waste storage and disposal. By providing adequate redox conditions that inhibit sulfate-containing water to reduce the sulfate attack on cement and concrete may facilitate the expected design performance of the concrete barrier. However, few studies have indicated that the conversion of sulfide to sulfate concomitantly occurs with pyrite oxidation and the accompanying creation of a reductive environment in the EBS to reduce the ettringite formation. Limited attention has been focused on redox processes that may markedly influence the formations of degradation materials from concrete (Berner 1992). Therefore, concrete degradation that is caused by the altered redox environment requires further investigation.
The hydrogeochemical environment of an LLW repository is determined by the composition of groundwater and mineral formation, which may influence the chemical compatibility of backfill material, the concrete barrier, and the buffer material in the near field. The durability of cementitious material in service environments has presented a number of concerns, such as whether the EBS may be completely isolated from the groundwater and the accompanying hydrogeochemical reactions and key aqueous species in the groundwater that affect the degradation of the concrete barrier of the repository, and the influence of the redox processes on the formations of degradation materials. To obtain further insights into these interactions and provide a detailed overview of the long-term evolution in the hydrogeochemical environment of the concrete barrier, a reactive chemical transport model of HYDROGEOCHEM 5.0 (Yeh et al. 2004) was used to assess the hydrogeochemical influences on concrete barrier degradation. The results of this study offer valuable information on the long-term behavior of the concrete barrier in the EBS.
Concrete barrier design
Chemical composition and corresponding clinker phases in Taiwan cement
Content % by weight
Na2O + 0.685K2O
Corresponding clinker component
Tricalcium silicate (C3S)
Dicalcium silicate (C2S)
Tricalcium aluminate (C3A)
Tetracalcium aluminate ferrite (C4AF)
Mixed proportion of concrete components and their physical properties
Content % by volume
Cement + Water
The groundwater quality data was limited because a groundwater monitoring well was not set up in the proposed site. Therefore, a thermodynamic equilibrium model, PHREEQCI (USGS 2010), was used to determine the equilibrium composition of the pore water as groundwater reacting with geological mineral of argillite at the site. The calculated results represented the groundwater quality of the proposed site in this study.
To evaluate the durability of the cementitious materials of the concrete barrier in the near field, a multi-species coupled geochemical transport model HYDROGEOCHEM 5.0 was used to simulate the reactive geochemical transport processes that are involved in the concrete degradation.
Chemical equilibrium model
The PHREEQCI is a complete windows-based graphical user interface version of the geochemical computer program PHREEQC (Parkhurst and Appelo 1999) which was developed by the U.S. Geological Survey, and provides all of the capabilities of the geochemical model PHREEQC, including speciation, batch-reaction, 1D reactive-transport, and inverse modeling.
Reactive chemical transport model
To assess the durability of the cementitious materials of the concrete barrier, a hydrogeochemical transport model HYDROGEOCHEM 5.0 was used to simulate the reactive chemical transport processes that are involved in the concrete degradation in the near field. The computer program HYDROGEOCHEM 5.0, developed by Yeh et al. (2001, 2004), is a 3-D numerical model of fluid flow, thermal, hydrologic transport, and biogeochemical kinetic and equilibrium reactions in saturated and unsaturated media. HYDROGEOCHEM 5.0 was designed for generic applications to reactive transport problems that are controlled by both kinetic and equilibrium reactions in subsurface media. The flow equations, chemical transport equations, chemical equilibrium equations, initial boundary conditions, and numerical methods of the model are described as follows.
The finite element method was used to solve Eqs. (1), (2), and (3), and the constitutive relationships among the pressure head, degree of saturation, and hydraulic conductivity tensor, together with the appropriate initial conditions and the five types of boundary conditions, which are Dirichlet, Cauchy, Neumann, variable, and surface-water boundary conditions. The temporal-spatial distributions of the hydrological variables, including pressure head, total head, effective moisture content, and Darcy’s velocity were obtained.
Chemical transport equations
Four types of boundary conditions (Dirichlet, Cauchy, Neumann, and variable inflow-outflow) were implemented in HYDROGEOCHEM5.0.
Chemical reaction equations
Let us assume that there are N E fast/equilibrium reactions (all of which must be independent) and N K slow/kinetic reactions, i.e., N = N E + N K .
Effect of precipitation/dissolution on porosity, hydraulic conductivity, water capacity and hydrodynamic dispersion
A two-step method was used to solve the chemical transport equations and chemical equilibrium equations. Once the solution for one time step converges, the calculation continues to the next time step. The finite difference (FD) methods were used for temporal discretization of the governing partial differential equations in the flow module and reactive transport module. The Galerkin finite element method was used for spatial discretization of the modified Richards equation that governs the distribution of pressure fields. For scalar reactive transport equations, either the conventional finite element methods or the hybrid Lagrangian–Eulerian finite element methods were used for spatial discretization. The chemical equilibrium equations were solved by the Newton–Raphson method or Picard method.
Thermodynamic data and PHREEQCI modeling
The composition and phase development of hydration products as the chemical reaction of cement with groundwater flow influences the lifetime performance of the concrete barrier. The thermodynamic modeling of Portland cement in the subsurface system of cementitious media was formulated and applied to assess the performance of concrete barriers.
Reactions considered in the HYDROGEOCHEM 5.0 model
Aqueous complexation reactions (25 °C)
H2O = OH− + H+
K+ + Cl− = KCl
Al3+ + 4OH− = AlO2 − + 2H2O
K+ + OH− = KOH
Al(OH)2+ = Al3+ + 2(OH)−
K+ + SO4 2− = KSO4 −
Al(OH)2+ = Al3+ + (OH)−
NaAlO2 + 2H2O = Al3+ + Na+ + 4OH−
Al(SO4) 2 − = Al3+ + 2SO4 2−
Na+ + Cl− = NaCl
AlSO2 + = Al3+ + SO4 2−
NaHCO3 = HCO3 − + Na+
Ca+2 + HCO3 − + OH− = CaCO3 + H2O
Na+ + H4SiO4 + OH− = NaH3SiO4(aq) + H2O
Ca2+ + Cl− = CaCl+
Na+ + HCO3 − + OH− = NaCO3 − + H2O
CaCl2 = Ca2+ + 2Cl−
Na+ + OH− = NaOH
CaHCO3 + = Ca2+ + HCO3 −
Na+ + SO4 2− = NaSO4 −
Ca2+ + OH− = CaOH+
HCO3 − + 9 H+ + 8 e− = CH4(aq) + 3 H2O
Ca2+ + SO4 2− = CaSO4
2 H2O = O2(aq) + 4 H+ + 4 e−
HCO3 − = CO2(aq) + OH−
2 H+ + 2 e− = H2(aq)
HCO3 − + OH− = CO3 2− + H2O
SO4 2− + 8 H+ + 8 e− = S2− + 4 H2O
HAlO2(aq) + H2O = Al3+ + 3(OH)−
SO4 2− + 9 H+ + 8 e− = HS− + 4 H2O
HCl +OH− = Cl− + H2O
SO4 2− + 10 H+ + 8 e− = H2S + 4 H2O
H4SiO4 + 2OH− = H2SiO4 2− + 2H2O
Fe+3 + e− = Fe+2
H2SO4 + 2(OH)− = SO4 2− + 2H2O
Fe+3 + 4 H2O = Fe(OH) 4 − + 4 H+
HSO4 − + OH− = H2O + SO4 2−
Precipitation-dissolution reactions (25 °C)
Molar volume (dm3/mol)
HCO3 − + Ca2+ + OH− = CaCO3 + H2O
Ca2+ + 2OH− = Ca(OH)2
2Al3+ + 6Ca2+ + 26H2O + 3SO4 2− + 12OH− = Ca6Al2(SO4)3(OH)12·26H2O
H4SiO4 = SiO2 + 2H2O
Ca2+ + SO4 2− + 2H2O = CaSO4·2H2O
2Al3+ + 3Ca2+ + 12OH− = Ca3Al2(OH)12
2Al3+ + 4Ca2+ + 2Cl− + 4H2O + 12OH− = 2Ca2Al(OH)6Cl·2H2O
3Ca2++H4SiO4 + SO4 2−+HCO3 −+11H2O +3OH− = CaSiO3·CaSO4·CaCO3·15H2O
2Al2+ +HCO3 − + 4Ca2+ + 3.68H2O + 13OH− = 3CaO·Al2O3·CaCO3·10.68H2O
FeS2 + 2 H+ + 2 e− = Fe+2 + 2 HS−
Rain water quality used in the thermodynamic equilibrium model
Concentration (Units: μmol/l)
HYDROGEOCHEM 5.0 simulation
Physical parameters used in HYDROGEOCHEM 5.0 model
Diffusion coefficient (m2/s)
Bulk density (kg/m3)
Longitudinal dispersivity (m)
Lateral dispersivity (m)
3.1 × 10−14
3.0 × 10−12
5.0 × 10−11
1.2 × 10−10
3.24 × 10−8
2.0 × 10−11
6.908 × 10−2
1.69 × 10−1
1.01 × 10−4
7.68 × 10−5
1.14 × 10−3
1.84 × 10−6
1.84 × 10−6
9.97 × 10−3
3.61 × 10−2
3.21 × 10−2
1.00 × 10−20
3.33 × 10−14
2.71 × 10−8
1.91 × 10−7
3.43 × 10−7
3.43 × 10−7
1.394 × 10−11
2.14 × 10−3
3.60 × 10−4
3.81 × 10−4
5.64 × 10−5
1.53 × 10−1
1.79 × 10−4
1.58 × 10−4
1.633 × 10−3
2.94 × 10−2
8.57 × 10−2
8.81 × 10−2
6.60 × 10−5
1.51 × 10−4
1.51 × 10−4
3.10 × 10−2
1.0 × 10−8
1.0 × 10−10
8.79 × 10−4
Case 1: LLW repository without side ditch and redox processes.
Case 2: LLW repository with side ditch and without redox processes.
Case 3: LLW repository with side ditch and redox processes.
This study considered limited chemical reactions under the chemical equilibrium condition; therefore, the comprehensive reactions of the cementitious phase and the chemical kinetics should be included in future reactive chemical transport simulations. Based on the simulated results, the hydrogen ion can result in the dissolution of portlandite and increases the concentration of calcium in the pore water. The sulfate anion reacts with cement to form ettringite. The chloride from the pore water enters the cementitious materials to form Friedel’s salt. Luna et al. (2006) pointed out that the ettringite can cause the volumetric expansion and eventually leads to fracturation processes. Excess of chloride can produce corrosion of the reinforcement element and cause a volume expansion which may lead to micro-fracturing in the concrete. Formation of ettringite and Friedel’s salt are also associated to a volume increase eventually leading to fracture formation and weaken the EBS (Lagerblad and Trägardh 1994). Seitz and Walton (1993) showed the detailed failure mechanisms for concrete vaults. They pointed out that, as cracks fully penetrate the concrete, the permeability of the vault increases. The cracks can also accelerate degradation rates. Thus, the water flow through cracks over extended periods is the primary concern for concrete performance of long life radionuclides (Seitz and Walton 1993). Moreover, seismic fractures may induce the coincided cracks and increase permeability. However, HYDROGEOCHEM 5.0 is not able to predict crack damage or its impact on permeability. The further quantification of concrete degradation caused by concrete cracks and numerical models coupled with thermo-hydraulic–mechanical–chemical processes should be developed to assess these impacts in the future.
A proposed site for final disposal of LLW of Daren is on the selected list in Taiwan. To investigate the hydrogeochemical reactions and effect on concrete degradation in the proposed LLW repository site, HYDROGEOCHEM 5.0 model was applied to simulate the complex chemical interactions between the cement minerals of the concrete and groundwater flow and reactive chemical transport resulting from water–rock interaction in the proposed site. Simulation results show the main processes responsible for concrete degradation involve geochemical reactive species induced from hydrogen ion, sulfate, and chloride. The intrusion of hydrogen ion from groundwater results the dissolution of portlandite. However, the portlandite still maintains alkaline condition in proposed LLW repository, the concrete used as a confinement material in EBS may remain in well durable condition. The sulfate-induced concrete degradation may form the ettringite and the chloride-induced concrete degradation form Friedel’s salt. Thaumasite and monocarboaluminate are also formed as carbonate aggregates by sulfate attack, and carbonate intrusion, respectively. The formation of ettringite, Friedel’s salt, thaumasite and monocarboaluminate may result a volume expansion. The EBS with the side ditch efficiently drains the ground water and lowers the concentration of concrete degradation induced species. The degree of concrete degradation on performance of EBS with side ditch is much lower than the disposal tunnel without the side ditch. Moreover, the redox processes significantly influence on the formations of degradation materials. Reductive environment in the EBS can reduce the ettringite formation in the concrete degradation processes. The results of the study provide a detail picture of the long-term evolution of the hydrogeochemical environment of the proposed LLW disposal site in Taiwan. The chemical kinetics effect should be included in future reactive chemical transport simulations. Moreover, the interaction among water and other minerals of cement, bentonite, and backfill materials in the near field, volume-expanded cracks and seismic induced-fractures should also be considered in the future research. The development of advanced numerical models that coupled with thermo-hydraulic–mechanical–chemical processes is especially welcomed.
WSL and CWL designed and carried out the numerical model simulation. MHL interpreted the results. WSL drafted the manuscript. CWL and MHL finalized the manuscript. All authors read and approved the final manuscript.
The authors thank the National Science Council, Republic of China, for financial support of this research under contract No. NSC 100-NU-E-002-003-NU, NSC 99-NU-E-002-003, NSC 98-3114-E-002-013 and NSC 98-3114-E-007-015. We thank Dr. Chihhao Fan for assistance with discussion in preparation of the manuscript, and suggestions for possible future works.
The authors declare that they have no competing interest.
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- Appelo CAJ, Postma D (2005) Geochemistry, groundwater and pollution, 2nd edn. A.A. Balkema Publishers, LeidenView ArticleGoogle Scholar
- Arcos D, Grandia F, Domènech C (2006) Geochemical evolution of the near field of a KBS-3 repository. SKB Technical Reports TR-06-16Google Scholar
- Arnold BW, Knowlton RG, Schelling FJ, Mattie PD, Cochran JC, Jow HN (2007) Taiwan industrial cooperation program technology transfer for low-level radioactive waste final disposal—Phase I. Sandia National Laboratories, SAND2007-0131Google Scholar
- Berner UR (1992) Thermodynamic modelling of cement degradation—impact of redox conditions on radionuclide release. Cement Concrete Res 22:465–475View ArticleGoogle Scholar
- Blanc PH, Bourbon X, Lassin A, Gaucher EC (2010a) Chemical model for cement-based materials: thermodynamic data assessment for phases other than C–S–H. Cement Concrete Res 40:1360–1374View ArticleGoogle Scholar
- Blanc PH, Bourbon X, Lassin A, Gaucher EC (2010b) Chemical model for cement-based materials: Temperature dependence of thermodynamic functions for nanocrystalline and crystalline C–S–H phases. Cement Concrete Res 40:851–866View ArticleGoogle Scholar
- Bruno J, ArcosD, Duro L (1999) Processes and features affecting the near field hydrochemistry: Groundwater-bentonite interaction. Svensk Kärnbränslehantering AB, SKB TR-99-29, p 56Google Scholar
- Dullien FAL (1979) Porous media. Academic Press, New YorkGoogle Scholar
- Dupray F, Laloui L (2014) Numerical analysis of canister movement in an engineered barrier system. Acta Geotech. doi:10.1007/s11440-014-0347-7 Google Scholar
- Galíndez JM, Molinero J (2010) On the relevance of electrochemical diffusion for the modeling of degradation of cementitious materials. Cement Concrete Res 32:351–359View ArticleGoogle Scholar
- Glasser FP, Marchand J, Samson E (2008) Durability of concrete—degradation phenomena involving detrimental chemical reactions. Cement Concrete Res 38:226–246View ArticleGoogle Scholar
- IAEA (1999) Near surface disposal of radioactive waste, IAEA safety standards series, requirements. IAEA-WS-R-1, Vienna, p 29Google Scholar
- IAEA (2001a) Performance of engineered barrier materials in near surface disposal facilities for radioactive waste, IAEA-TECDOC-1255, Vienna, p 50Google Scholar
- IAEA (2001b) Technical considerations in the design of near surface disposal facilities for radioactive waste. IAEA-TECDOC-1256, Vienna, p 53Google Scholar
- Jantzen C, Johnson A, Read D, Stegemann JA (2010) Cements in waste management. Adv Cement Res 22(4):225–231View ArticleGoogle Scholar
- Lagerblad B, Trägardh J (1994) Conceptual model for concrete long time degradation in a deep nuclear waste repository. Swedish Cement Concrete Res Inst, SKB TR 95-21Google Scholar
- Luna M, Arcos D, Duro L (2006) Effects of grouting, shotcreting and concrete leachates on backfill geochemistry. Svensk Kärnbränslehantering AB, SKB R-06-107, p 51Google Scholar
- Parkhurst DL, Appelo CAJ (1999) User’s guide to PHREEQC (Version 2)—a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations: U.S. Geological Survey Water—Resources Investigations Report 99-4259. U.S. Geological Survey, DenverGoogle Scholar
- Seitz RR, Walton JC (1993) Modeling approaches for concrete barriers used in low-level waste disposal. U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 NRC FIN A6858Google Scholar
- Taiwan Cement Company (2011) http://www.taiwancement.com/. Taiwan Cement Company
- Taiwan Power Company (2010) Performance assessment in low-level radioactive waste disposal facility, version B. Taiwan Power Company, Taiwan (in Chinese) Google Scholar
- USGS (2010) PhreeqcI—a graphical user interface for the geochemical computer program PHREEQC. http://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqci/
- Yeh GT, Siegel MD, Li MH (2001) Numerical modeling of coupled fluid dlows and reactive transport including fast and slow chemical reation. J Contam Hydrol 47:379–390View ArticleGoogle Scholar
- Yeh GT, Sun J, Jardine PM, Burgos WD, Fang Y, Li MH, Siegel MD (2004) HYDROGEOCHEM 5.0: a three-dimensional model of coupled fluid flow, thermal transport, and hydrogeochemical transport through variably saturated conditions—version 5.0, ORNL/TM-2004/107. Oak Ridge National Laboratory, Oak Ridge, p 243Google Scholar