Cover
Title
Copyright
Preface
CHAPTER 1: International Context
1. A Review of the Effectiveness of Strategies to Manage Expansive Chemical Reactions in Dams and Hydro Projects
2. Swelling Dams in Switzerland
CHAPTER 2: Physico-Chemical Mechanisms. Experimental Test
1. Behavior of Concrete Deteriorated by ASR under Triaxial Load
2. Importance of Alkali-Wrapping for CPT
3. Structures Damaged by ASR and DEF: Improving the Prognosis of Structures Damaged by Expansive Concrete with Physico-Chemical Modelling
4. Can Certain Alkali Minerals Explain the Slow Reactivity of Granitic Aggregates in Dams?
5. Experimental Study on Effects of Aggregates Mineralogical Composition and Preservation Conditions on DEF in Concrete
6. The Identification, Extent and Prognosis of Alkali-Aggregate Reaction Related to Existing Dams in Switzerland
7. Experimental Evidence for the Link Between Aggregate Degradation and Expansion and the Formulation of the Microstructural Model
8. A Robust Testing Protocol for the Assessment of ASR Reactivity of Concrete
CHAPTER 3: Structural Modeling
1. Modeling of Environmental Conditions and their Impact on the Expansion of Concrete Affected by the Alkali–Silica Reaction
2. Nonlinear Finite Elements for the Assessment of Hydraulic Concrete Structures Affected by Alkali-Aggregate Reaction: A Study Case
3. Macro-Modelling of AAR-Affected Hydraulic Structures: Assessment of Parameters Influencing the In-Situ Concrete Growth
4. AAR and DEF Structural Effects Modelling
5. Swelling Effects in Fagilde Dam (Portugal): First Approach to Structural Analysis and Interpretation
6. Expansions in a Concrete Dam with Bridge over Spillway in South America: Case Study with Expansions of Different Origin
7. Modeling Concrete Expansions via Coupled C-M Mesoscale Analysis with Zero-Thickness Interface Elements, and Lab Experiments
CHAPTER 4: Dams and Hydraulic Structures Applications. Remedial Works
1. Numerical Analysis of AAR Affected Structures with Slot-Cuts: Finite Element Analysis Using Explicit Scheme
2. Swelling Arch Dams with Thrust Blocks
3. Bimont Dam Case: Studies and Investigations Inside the Dam Body
4. Chambon Dam: A Struggle against AAR
CHAPTER 5: Long-Term Behavior. Risk Reduction
1. The Diagnosis and Prognosis of ASR and ISR in Miranda Dam, Portugal
2. Long-Term Behaviour of EDF Dams Regarding Concrete Swelling Structures: Synthesis of Monitoring Data Over Time
3. Important Lessons Learnt from the Proper Surveillance of Swelling Concrete
Index of Authors
End User License Agreement

List of Tables

CHAPTER 1: International Context
1. Table 1. Summary of Dam Type and Interventions
CHAPTER 2: Physico-Chemical Mechanisms. Experimental Test
1. Table 1. Mix designs for the reactive and the non-reactive concretes
2. Table 2. Loading configurations used in the tri-axial cells
3. Table 1. Generated phases in wrapping cloths (Yamada et al., 2016a) Aggregate – highly reactive andesite, alkali content – 3.0 kg/m³, age – 45 weeks
4. Table 2. Alkalis in water-wrapping cloth after curing at 40°C for 26 weeks
5. Table 3. Elements in water-wrapping cloth after curing at 60°C for 4 or 40 weeks * After HCl extraction, something was still remained in wrapping cloth and the amount is assumed to be silica
6. Table 1. Characteristics observed under petrographic microscope of granitic rocks which may contribute to ASR
7. Table 2. Chemical composition of the granites (%)
8. Table 3. Mineral composition of the granites obtained by point counting
9. Table 1. Concrete composition
10. Table 2. Effects of thermic treatment on mechanical properties
11. Table 3. Impact of DEF on mechanical properties
12. Table 1. Classified (letters A to J) Standard & Validating/Supplementary AAR Identification, Extent and Prognosis Tests
13. Table 2. Influencing Factors – Standard AAR Identification, Extent and Prognosis Tests
14. Table 3. Limits, Observations, Advantages and Disadvantages of Recommended (*) and Standard AAR Identification, Extent and Prognosis Tests
15. Table 4. Influencing Factors for Validating/Supplementary AAR Identification, Extent and Prognosis Tests
16. Table 5. Limits, Observations, Advantages and Disadvantages for Validating/Supplementary AAR Identification, Extent and Prognosis Tests
17. Table 1. Testing conditions of the expansion tests
CHAPTER 3: Structural Modeling
1. Table 1. Some input data used for the multi-physical analysis in QSE-FE-S
2. Table 2. Results of the stability analysis
3. Table 1. Example of correction of instrument readings for cracking
4. Table 1. Concrete composition
5. Table 2. Concrete compressive strength (cubic samples of 20 cm edge)
6. Table 3. Swelling parameters considered in the dam’s zoning
CHAPTER 4: Dams and Hydraulic Structures Applications. Remedial Works
1. Table 1. Residual expansion between 8 and 106 weeks in µm/m/year
CHAPTER 5: Long-Term Behavior. Risk Reduction
1. Table 1. Cement physical characteristics (HED 1983)
2. Table 2. Cement chemical characteristics (HED 1983)
3. Table 3. Cement heat of hydration (HED 1983)
4. Table 4. Cores extracted from the dam
5. Table 5. Concrete residual expansivity test results
6. Table 6. Concrete tensile splitting strength test results
7. Table 7. Stiffness damage test results
8. Table 1. Cahora Bassa Dam: Carlson strain gauges: Average strain rates excluding those around the spillway openings

List of Illustrations

CHAPTER 1: International Context
1. Figure 1. Type and height of the dams in function of the year of construction
2. Figure 2. Monitoring devices available in concrete dams (subdivision in dam classes)
3. Figure 3. Presence of trends in class I dams (the values around the pie chart indicate the number of dams)
4. Figure 4. Presence of trends in the Swiss concrete dams (90% of the dams) (the values around the pie chart indicates the number of dams)
5. Figure 5. Presence of trends as function of the dam type
6. Figure 6. Percentage of dams with trends in relation with the geological zones of Switzerland
7. Figure 7. The assessment of the causes for dams exhibiting trends
8. Figure 8. Time of initiation of the observed concrete expansion in various dams represented in function of the year of construction
9. Figure 9. Horizontal drift rate compared with the seasonal elastic variation (30 dams)
10. Figure 10. Horizontal drift of gravity dams in function of the orientation of the dam axis (dam axis normal to the faces and oriented towards downstream)
11. Figure 11. Average vertical expansion rate over the whole dam height (26 dams)
12. Figure 12. Average vertical expansion over the whole dam height (20 dams)
CHAPTER 2: Physico-Chemical Mechanisms. Experimental Test
1. Figure 1. Schematic view of the triaxial setup
2. Figure 2. Longitudinal and radial free expansion observed by Dunant
3. Figure 3. Radial and axial delayed strain of concrete samples due to ASR and fluid pressure submitted to the different loading configurations
4. Figure 4. Micro-cracking pattern induced by ASR in aggregates
5. Figure 5. Meso-scale crack pattern induced by ASR in aggregates
6. Figure 6. Maps of the macroscopic cracks pattern (the stress is applied along the vertical direction)
7. Figure 7. Pseudo Young modulus tests vs axial stress σ_a
8. Figure 1. Comparison of CPT with and without AW (Yamada et al., 2016a). Aggregate type: curing temperature (°C); alkali content: AW; WI: late expansive hornfels; TO: rapid reactive andesite in the pessimum proportion
9. Figure 2. Wrapping procedures for AW-CPT
10. Figure 3. Initial and final alkali contents (Yamada et al., 2016a). N: very highly reactive andesite (expansion at 45 weeks – 0.06-0.17%); N-FA: fly ash contained (exp. – 0.04-0.09%); T: chert (exp. – 0.02-0.07%); T-fine: chert as fine aggregate (exp. – 0.07%)
11. Figure 4. Expansion and mass change for aggregates N and LS with various NaOH concentration in WA (60°C, total alkali content – 5.5 kg/m³)
12. Figure 1. Aggregate scale – Ions transport and silica reactivity (Na_f: alkali fixed in ASR-gels)
13. Figure 2. Concrete scale – ions diffusion and alkali fixation
14. Figure 3. Expansion according to moisture conditions in (Poyet et al. 2006) (points) and modelling
15. Figure 4. Pessimum of expansion according to curing duration at 85°C, experimental points from (Brunetaud et al. 2008)
16. Figure 5. DEF-expansion according to alkali leaching, experimental points from (Famy et al., 2001)
17. Figure 1. Aggregate GR2: deformation of the rock reflected in sub-graining of the quartz. Plagioclase (pl) is altered, mainly in the core of the zoned crystal, and microcline (mc) does not show alteration (Crossed Polarized Light – CPL)
18. Figure 2. Aggregate GR23-A: crystals of microcline (mc) and plagioclase (pl). Plagioclase is altered to sericite and calcite (cc), mainly in the cores of the crystals (CPL)
19. Figure 3. Aggregate GR24-A: crystal of zoned plagioclase (pl). Albitization of K-feldspar (orthoclase - or) crystal and alteration of albite (pl-ab) to clay minerals (CPL)
20. Figure 4. Aggregate GR29: perthitic microcline (mc) and plagioclase (pl) crystals. Biotite (bt) lamellae are partially replaced by chlorite (chl) (CPL)
21. Figure 5. Na₂O and K₂O (%) contents released with time by granitic aggregates in alkaline solutions (Notation: N – not altered rock; A – altered rock)
22. Figure 6. Na₂O_eq. (%) content released with time by granitic aggregates in alkaline solutions (Notation: N – not altered rock; A – altered rock)
23. Figure 1. Heating treatment
24. Figure 2. Swelling of concrete samples with siliceous or calcareous aggregates
25. Figure 3. Dynamic Young Modulus evolution of concrete samples with siliceous or calcareous aggregates
26. Figure 4. Tomographic monitoring of samples with siliceous aggregates. Mean diameter: 6mm, voxel size: 4µm. a.7 days, b. 5 months, c. 1 year
27. Figure 5. Observations of samples with a scanning electron microscop. a. Vein of compressed ettringite at the aggregate-cement paste interface, b. Void with free ettringite formation and aggregate covered with compressed ettringite
28. Figure 6. Impact of drying cycles on the swelling of concrete samples
29. Figure 7. Impact of drying cycles on DEF amplitude
30. Figure 1. Schematic view of elements affecting the selection of AAR testing core samples
31. Figure 2. Recommended (*) and other Standard AAR Tests (Hammerschlag et al. 2005)
32. Figure 3. Proposed Strategic method for Dam AAR Identification, Extent and Prognosis Evaluations (Squared-bracketed numbers refer to the references provided in Table 1 to 5)
33. Figure 4. Temperature field influence lines
34. Figure 5. Influence line Method for AAR Core Sample Zoning
35. Figure 6. AAR Zoning for Core Sample Selections (colours indicate different levels of affected and non-affected AAR regions)
36. Figure 7. Different Phases of AAR Residual Expansion Prognosis Tests based on Longitudinal Direction Expansion Measurements on Core Samples (Merz et al., 2013)
37. Figure 1. Damage patterns as well as comparison between the predicted expansion and reaction and the experimental observations. The experimental observations overstate the damage in the aggregates due to the sample preparation.
38. Figure 2. The damage patterns predicted by a reaction occurring on the surface of the aggregates are very different from the experimental observations. Subsequent theoretical developments by Charpin corroborated this result
39. Figure 3. Predicted and observed expansions. The experimental samples probably underwent leaching, which explains why he predicted expansion most closely matched the higher alkali samples
40. Figure 4. Degradation of the concrete as predicted by the model. The morphology of the damage matches closely the microscopic observations
41. Figure 5. The degradation predicted by the model follows well the experimental observation in the early stages of the reaction. In this instance, as creep is not taken into account, the predicted loss of stiffness eventually overestimates the experiment
42. Figure 6. Damage simulations using a visco-elastic paste model require distinguishing between strain and stress based fracture criteria, unlike quasistatic simulations for which they are equivalent. Using a stress-based criterion, the loads on the paste are relaxed
43. Figure 7. Predicted damage in the paste and aggregates for two rates of loading. The difference in the damage pattern is clear when comparing to the simulations using a quasistatic model as presented above
44. Figure 1. Expansion over time for some of the studied system (cf. Table 1)
45. Figure 2. Na₂O_eq leaching over time evolution
CHAPTER 3: Structural Modeling
1. Figure 1. Expansion of concrete at different temperatures subjected to the AW-CPT
2. Figure 2. Arrhenius plot of each parameter of Equation (2)
3. Figure 3. Environmental conditions of the exposure sites
4. Figure 4. Expansion of field-exposed blocks
5. Figure 5. Modeled temperature variations over different averaging periods (Fukuoka)
6. Figure 6. Simulated expansions under different water supply conditions (the averaging period is 1 day, and the legend indicates the water supply condition (Table 1))
7. Figure 7. Effect of the averaging period on the simulated expansion under different water supply conditions
8. Figure 8. Effect of water supply on the simulated expansion (1 month-averaging)
9. Figure 1. (a) Description of the structural problem; Assessment methodology: (b) continuous and (c) instantaneous
10. Figure 2. Numerical framework for the QSE-FE-S: (a) user-subroutine implementation; (b) multi-physical approach (Ben Ftima et al. 2016)
11. Figure 3. FE model of the hydraulic structure and results of QSE-FE-S (Ben Ftima et al. 2016): (a) Geometry and mesh; (b) Predicted damage pattern (damaged elements in blue) and (c) real cracking pattern record
12. Figure 4. (a) Model, (b) Load conditions of the identified potentially instable concrete wedge and (c) FE mesh for the QSE-FE-D analysis
13. Figure 1. (a) Incorporation of the exponential law, (b) AAR expansion over time vs. life span of a structure
14. Figure 2. Variation of the ASR expansion in function of the relative humidity
15. Figure 3. Effect of RH on the AAR expansion
16. Figure 4. (a) Test results on reduction of AAR expansion with the steel ratio (b) Geometry of the model used for validation (c) Comparing analysis results to experimental values
17. Figure 5. Simplified Curve on reduction of AAR expansion with the steel ratio obtained from available test results and numerically calculated
18. Figure 6a. Confinement effect in function of volumetric stress
19. Figure 6b. Variation of in-situ rate of expansion in right-left bank direction;(a) 5, (b) 18, (c) 50 years after construction respectively
20. Figure 7. Stress state of the thin-walled circular member
21. Figure 8. Variation of volumetric confinement parameter in function of volumetric stress
22. Figure 9. (a) Reduction of volumetric expansion of 40%; (b) evaluation of the uniaxial confinement parameters for each direction
23. Figure 10. (a) – Calculation of percentages of expansion. (b) Distributed expansion rates in each direction.
24. Figure 11. (a) moderate macro-cracks through the entire height of the unit; (b) The position of instruments in the unit of the powerhouse; (c) extensive cracking and deformation in the pier of the draft tube, over a region of 2.0 m
25. Figure 12. (a) Location of the instruments; (b) Damage distribution
26. Figure 13. Two examples only: comparison of measured and calculated displacements
27. Figure 14. The damage is expressed with the damage parameter β for the year 2010
28. Figure 15. Damage predicted for the year 2033; Pier strengthened in 2010 by 35M rebars
29. Figure 1. Rheological scheme of the model
30. Figure 2. Strains effect on gel pressure
31. Figure 3. Global methodology summary
32. Figure 4. Principle of the chemical advancement assessment
33. Figure 5. Volume de gel influence
34. Figure 6. Comparison of measured and computed deformations in 3D
35. Figure 7. Vector view of the computed stress state
36. Figure 8. Comparison between evaluated damage and observed cracking pattern
37. Figure 9. Dam reinforcement with tendons – Downstream view
38. Figure 1. Fagilde dam. Downstream view
39. Figure 2. Accumulated vertical displacements between 1985 and 2015 at the crest, obtained from the results of geodetic levelling
40. Figure 3. Accumulated horizontal displacements (river axis direction) between 1985 and 2015 near the crest, obtained from the results of geodetic methods
41. Figure 4. Cracking pattern of the downstream surface in 2009
42. Figure 5. Downstream views of the bottom zone of the right arch (on left) and of the upper zone of the left arch (on right), in 2015
43. Figure 6. General view (on left) and detailed view (on right) of the central buttress, in 2016
44. Figure 7. Free swelling curve obtained in isothermal tests
45. Figure 8. General view of the finite element mesh (on left) and mesh details at the insertion surface (on right)
46. Figure 9. Water load discretization used in structural analysis
47. Figure 10. Swelling patterns computed for the arches and for the central buttress in 1995, 2005 and 2015
48. Figure 11. Vertical displacements, observed and computed, since 1985 to 2015
49. Figure 12. Principal stresses computed on dam surfaces in 2015
50. Figure 1. View of the downstream face of the dam and the bridge over the spillway
51. Figure 2. Cracks in piles: a) in the contact with the spillway and b) in construction joints
52. Figure 3. Alkali-silica gel
53. Figure 4. a) Ettringite needles, b) detail of ettringite needles, c) sulfoaluminate phases covered by product of reaction and d) detail of the ettringite needles covered by the gel
54. Figure 5. Maximum temperature reached in each point for construction rate V1
55. Figure 6. Influence of the maximum energy released in the hydration in the maximum temperature reached at the center of different layers (at different heights)
56. Figure 7. a) Diagonal cracks in the piles and b) phenomenon causing the cracks
57. Figure 1. 3D simulations at the meso-level of external sulfate attack to concrete after 740 days. In figures (a) and (b) aggregates have been removed to ease the visualization
58. Figure 2. Configuration of active specimens used in ASR interfacial expansion tests and schematic representation of the three sets of specimens tested with different lateral sealing
59. Figure 3. Interfacial expansion curves: Set #1 - specimens without lateral sealing; set #2 - specimens with complete lateral sealing; set #3 - specimens with lateral sealing only on the HCP-glass interface zone
60. Figure 4. Machine used for ASR expansion tests under “true” triaxial confinement states
61. Figure 5. Schematic representation of ASR mechanism in concrete
CHAPTER 4: Dams and Hydraulic Structures Applications. Remedial Works
1. Figure 1. Flow-Chart of the Hydro-Quebec’s AAR Modeling Methodology
2. Figure 2. Effect of sudden release of boundary condition in explicit analysis: a-Displacement after release and b – Kinetic Energy
3. Figure 3. Smooth Step function used for gradual reduction of stiffness before element removal
4. Figure 4. Interruption of AAR’s time-dependent properties for slot-cutting duration: a- AAR expansion and b- Elastic modulus degradation
5. Figure 5. Validation of slot-cutting material with a concrete bloc – Model
6. Figure 6. Validation of slot-cutting material with a concrete bloc – Stress in slot-cut material
7. Figure 7. Validation of horizontal displacements during slot-cutting with a concrete bloc
8. Figure 8. Geometry of the theoretical 3-unit structure used for validation purposes: a- Upstream view; b- Downstream view; c- close-up on slot-cut zone
9. Figure 9. Kinetic energy and horizontal displacement for the 3-unit model
10. Figure 10. Stresses in the longitudinal direction for the 3-unit model – (a) before and (b) after slot-cutting
11. Figure 11. AAR expansion rate variation for the 3-unit model – (a) longitudinal and (b) vertical direction. In the longitudinal direction, the average expansion rate increases 430% after the cuts. In the vertical direction, the increase is 35%
12. Figure 12. An example of a real structure analysis with slot-cutting and validation with in-situ measurements
13. Figure 13. The location of the 1972-73 slot-cutting and the concrete damage as a consequence of this intervention: (a) the increased macro cracking in the water passage of group A of the intake structure and (b) sheared stay wanes of units A and B following the slot-cutting at the junction of the intake structure and the right Gravity Dam.
14. Figure 14. Slot-Cutting – between the units 35 and 36 (1980–1981)
15. Figure 15. Slot-Cutting – between the units 35 and 36 (1980–1981); development of extensive concrete cracking in unit 36 fife (5) years after the slot-cutting in 1981
16. Figure 1. Schematic Elevation of a simple thrust block (USACE)
17. Figure 2. Horizontal arch strains in function of thrust block heights, for 10 studied dams
18. Figure 3. Example of an “L” thrust block
19. Figure 4. Linear model and non-linear model with contraction joints in winter situation
20. Figure 5. Linear model and non-linear model with concrete-to-rock joint on a swelling arch dam with thrust blocks
21. Figure 6. Linear to non-linear model with concrete-to-rock joint. Stress reorientation and modification on the upstream face
22. Figure 7. Seasonal reversible displacements (seasonal heating) measured on thrust blocks of 4 arch dams
23. Figure 1. Bimont Arch Dam
24. Figure 2. Cantilever 2 crest levelling showing the swelling evolution (1: Unknown previous swelling; 2: Joint B re-grouting – March 1969; 3: Swelling after March 1969; 4: Beginning of levelling survey; 5: P2 crest plumbline installation; 6: P7 crest plumbline installation)
25. Figure 3. Drilling and swelling zones location (in white)
26. Figure 4. Concrete sample area S4: Expansive Secondary ettringite, MEB, polish section, SEI, HV, various zooms (extract from LMDC Report)
27. Figure 5. Expansion test on hardened concrete (extract from LMDC Report)
28. Figure 6. Dam mesh: (1) Joint between two blocks, (2) Swelling areas and (3) Joint along the dam footprint
29. Figure 7. Cracking mechanism around swelling areas: (1) P4 Swelling area of P4, (2) Increase of the swelling bloc, (3) Shear stress at the origin of cracks and (4) Plastic strain (≈ cracks in the normal plan)
30. Figure 8. Developed downstream view of the dam right bank – Left: Plastic strains showing the internal cracks area. Right: Extension of internal crack area as deduced from investigations
31. Figure 9. Principal stress on downstream face after swelling with a water level of 329
32. Figure 10. Anchor drilling (black) and grouting (blue) locations – downstream elevation
33. Figure 11. Anchor drilling (black) and grouting (blue) locations – section of cantilever 3
34. Figure 12. Joints grouting – Horizontal section between El. 315,00 and 318,00
35. Figure 1. Chambon dam plane view
36. Figure 2. Main swelling deformation rate at Chambon dam between 1984 and 1994
37. Figure 3. Repair works conducted in the 1990’s in relation with AAR a: crack grouting, b: old spillway concrete, c: upstream sealing, d: slot cuts
38. Figure 4. Displacement of pendulum in the left curved wing before and after the works
39. Figure 5. The vertical drainage curtain seen from downstream and cross section
40. Figure 6. Comparison of measured and computed deformations in 3D modeling
41. Figure 7. The predicted swelling in the future at Chambon dam
42. Figure 8. The principal stresses tensors calculated in the dam
43. Figure 9. The tendons pattern (red) and drainage curtain seen from downstream
44. Figure 10. The carbon fiber net seen from upstream
45. Figure 11. Carbon fiber net anchoring device
46. Figure 12. The design of the new campaign of slot cutting
CHAPTER 5: Long-Term Behavior. Risk Reduction
1. Figure 1. Miranda dam. Downstream view and buttress profile (Batista & Gomes 2016)
2. Figure 2. Identification of the concretes used in the different areas of the buttress, through their cement content (205, 225, 250 and 275 kg/m³)
3. Figure 3. Miranda dam. Results of quantitative analysis of vertical displacements at the top of the central buttress, obtained from geodetic levelling, between 1963 and 2014
4. Figure 4. Identification of the core extraction locations
5. Figure 5. Aggregate potential reactivity test results (left: AAR-4.1, right: AAR-3.1)
6. Figure 6. Concrete ultimate expansivity test results
7. Figure 7. Concrete compressive strength test results (in blue) and estimated values (in red)
8. Figure 8. Stiffness damage test results (in blue) and estimated values (in red)
9. Figure 1. Dams on which enough data was available for swelling identification and quantification, referring to 2007 study
10. Figure 2. Vertical swelling rates observed
11. Figure 3. Vertical swelling rates observed on dam n°18
12. Figure 4. Arc elongation on crest of arch dams
13. Figure 5. Vertical rate versus horizontal rate of swelling (on 8 arch dams)
14. Figure 6. Dams identified with swelling, and building dates
15. Figure 7. Localization of swelling dams
16. Figure 8. Strain kinetics modeled on 8 dams using monitored data from embedded extensometers
17. Figure 9. Fitting of the monitoring data with f(t^x) and (1≤x≤2.5)
18. Figure 10. Tangential and vertical strains modeled since first impoundment on 30 dams
19. Figure 11. Comparison of total arc elongation strain with the seasonal deformation
20. Figure 1. Downstream view of Cahora Bassa Dam
21. Figure 2. Cahora Bassa Dam: Layout of the rod extensometers
22. Figure 3. Cahora Bassa Dam: Rod extensometers: Annual strain rate of the concrete
23. Figure 4. Cahora Bassa Dam: Layout of Carlson strain gauges
24. Figure 5. Cahora Bassa Dam: Carlson strain gauges: strain directions for the different installations
25. Figure 6. Cahora Bassa Dam: Carlson strain gauges: “Stress free” strain at the top of the dam wall above RL 300 m
26. Figure 7. Downstream view of Kouga Dam (previously named Paul Sauer Dam)
27. Figure 8. Kouga Dam: Vertical displacement at the centre of the dam 4 m below full supply level
28. Figure 9. Kouga Dam: Horizontal displacement at a quarter point of the dam on the right flank (looking downstream) 4 m below full supply level

Preface

Swelling of concrete occupies a major role in the long term concerns of owners and operators of dams and hydraulic structures. The mean age of dams in European countries, for example, is now well over 50 years.

Faced with irreversible movements of their dams or with observed cracking processes, operators need to explain the observed phenomena, justify safety conditions and in some cases plan remedial works. Underlying these concerns, the question of life duration of the structures is raised.

During the last twenty years active research has been carried out in the field, resulting in practical results in phenomena interpretation and dam modeling. An increasing number of affected dam cases have been documented, with safety reevaluations and in some cases remedial works. A small number of them have been demolished.

If it still remains difficult to establish ‘a state of the art’ in this domain due to the rapidly evolving context, regular international exchanges in the field appear fruitful and necessary.

Therefore, in the continuity of previous conferences in the field organized under the lead of Robin Charlwood, former President of the ICOLD Concrete Committee (Fredericton 1992 / Chattanooga 1995 / Grenada 2007 / Paris 2009 / Fontana 2013), EDF and Toulouse University-LMDC have taken the initiative to organize in Chambéry, located in the historical heart of Savoy, a workshop intending to provide a new opportunity for experience sharing and benchmarking.

The aim of the workshop is to assemble active researchers, leading engineers and experts from the practicing community and administration interested directly or indirectly in concrete swelling effects in dams and hydraulic structures. All kinds of chemical expansion phenomena, including those due to alkali aggregate reactions and those due to ettringite formation are addressed.

These proceedings include 24 papers written by renowned experts in their own field. They are divided in five chapters:

Chapter 1 provides an overview of the international context of affected hydraulic structures and a focus on Swiss dams. All continents seem to be concerned and even if temperature plays a significant kinetic role, structures in cold regions are also affected. Concrete swelling consequences strongly depend upon geometrical configurations. Interactions with electromechanical components are a main issue. A large panel of solutions are available and have already been used to minimize disorders.

Chapter 2 is devoted to physicochemical mechanisms and experimental tests. Thanks to significant work performed in the field, a real increment in the comprehension of the mechanisms can be assessed. Multiscale approaches, from aggregate to concrete scale, from chemical equations to structural modeling, enable an optimal weighting of the different mechanisms and may explain the apparent discrepancies in test results. The importance of ambient conditions (temperature, humidity, alkali content) and test procedures is highlighted. Improvements in experimental conditions and methodology are proposed. Several works focus on the importance of aggregate types in AAR but also in DEF, in relation to alkali release from granitic stone, different effects of transition zones in calcareous or silica aggregates, or to the localization of AAR inside granulates. Coupling between ASR and DEF is also now better understood through the common role played by alkalis in silica gel and ettringite formation. Thanks to available experiments related to the influence of stresses on swelling kinetics, a best estimation of confinement effects in hydraulic structures is practicable. Faced with the great diversity of tests and investigations facilitating the identification, extent and prognosis of AAR, methodological approaches and guidelines are required and proposed.

Chapter 3 presents several models dedicated to the swelling mechanisms of concrete and their structural effects. Among the main phenomena considered, all the models adopt common assumptions to consider effects of environmental conditions (temperature and humidity). A first one focuses specifically on these environmental conditions and shows the importance of rainfall periods on swelling kinetics, especially for thin structural elements. The aptitude of structural models to consider the swelling anisotropy under complex stress states is also considered as important for practitioners; it is illustrated through different applications relative to dam analysis. The possibility of using an original explicit scheme to accelerate the numerical solving of these nonlinear models is presented. Concerning the links between chemical reactions, swelling and induced damage, they are considered at different scales of analysis, with, for the finest scale, a mesoscopic model able to link ionic diffusion and swelling kinetics at the aggregate-paste interface, until different macroscopic formulations clarified in the context of classical continuum mechanics. In the latter case the swelling is either an anisotropic imposed strain depending on the stress state via empirical laws, or is based on a poro-mechanical formulation able to link the gel volume produced by the ASR, the gel pressure and the stress state via plasticity criteria controlling simultaneously the anisotropy of damage and swelling. Some analyses also show that other delayed strains of concrete (creep and shrinkage) should not be neglected compared to ASR swelling. Regarding DEF, a realistic estimation of thermal conditions at early age is a necessary step as demonstrated on a real dam case.

Chapter 4 is dedicated to the description and presentation of remedial works. It illustrates the fruitful processes including physico-mechanical approaches, experimental tests, in-situ measurements and models calibrated to monitoring results. They enable to orientate interventions, accommodate concrete swelling and estimate the impact of invasive interventions such as slot cutting. Beyond the similarities, each type of structures reveals its particularities and adaptation possibilities. The particular case of arch dams with thrust blocks illustrates the need to distinguish between external loading and internal loading such as thermal or swelling effects. For the latter, efforts are induced by the structure’s confinement and can be released through adaptation processes. Bimont and Chambon dams illustrate cases where extensive remedial works programs have been carried out, for a second time in the case of Chambon dam.

Chapter 5 is devoted to the long term management of hydraulic structures. Estimation of the residual swelling potential appears to be, in this respect, a main issue. Even if long time extrapolation remains questionable, test procedures seem able to operate a distinction between concrete reactivity levels and thus to classify works sensitivity. The importance of monitoring and device redundancy is highlighted.

In conclusion, the different papers illustrate the need to progress through interdisciplinary approaches when faced with such complex engineering problems, requiring complex engineering solutions. In order to ensure an operation progresses in good conditions, a methodology based on the combined use of monitoring (irreversible evolution measurements), laboratory tests (pathology identification, swelling kinetics and potential), numerical modeling (historical behavior simulation, safety evaluation, future evolution, remedial works efficiency evaluation) and remedial works implementation (waterproofing, injections, sawing, anchoring …) seems to bring consensus.

Finally the organizers would like to gratefully acknowledge the support of ICOLD and CFBR, Toulouse University and Electricité de France and thank the hospitality of the Hydro Engineering Centre of EDF for their organisational support.

Alain Sellier	Professor (LMDC-Toulouse University)
Étienne Grimal	Dam Specialist (EDF-CIH)
Stéphane Multon	Assistant Professor (LMDC-Toulouse University)
Éric Bourdarot	Dam Expert (EDF-CIH)

Swelling Concrete in Dams and Hydraulic Structures

DSC 2017

Preface