Some Dam AAR Milestones…. AAR in Dams and Hydroelectric Plantscivil.colorado.edu/~saouma/AAR/Library/Paris-2009/01-Charlwood.pdf · AAR in Dams and Hydroelectric Plants Robin G

1

AAR in Dams and Hydroelectric Plants

Robin G Charlwood, Ph.D., P.E.Chairman, ICOLD Committee on Concrete Dams, and

Principal, Robin Charlwood & Associates, Seattle, WA, USA

Short Courseon

Management of Alkali Aggregate Affected Structures: Analysis, Performance & Prediction

Hosted by

Coyne & Bellier, Paris, FranceSeptember 15, 2009

15 September 2009 1Robin Charlwood

Some Dam AAR Milestones….• USBR’s American Falls Dam 1927, Parker and Stewart Mountain 1930’s• TVA’s Fontana Project built in 1940, cored slots 1970• NB Power’s Mactaquac project built 1967, diamond wire saw cut slots 1988• Chambon Dam with slot cuts +upstream membrane, 1990?• ICOLD Bulletin 79 on AAR published in 1991 by Committee on Concrete• 1992 CANCOLD/CEA 1st International Conference on AAR in Hydroelectric

Plants and Dams - Fredericton, NB, Canada• 1995 USCOLD 2nd International Conference in Chattanooga, TN, USA

2001 6th B h k W k h M d li f AAR i D S l b• 2001 – 6th Benchmark Workshop, Modeling of AAR in Dams – Salzburg, Austria – ICOLD, Hosted by Verbundplan

• 2005 – 8th Benchmark Workshop, Evaluation of AAR Effects on a Gravity Dam– Wuhan, China – ICOLD, Hosted by CHINCOLD

• 2007 U Colorado Boulder Short Course on AAR• 2007 - Workshop on AAR in Hydroelectric Projects and Dams – Granada,

Spain – ICOLD/SPANCOLD – Hosted by Int. J on Hydropower & Dams• 2010 – New Bulletin, Chemical Expansion of Concrete in Dams - ICOLD

Committee on Concrete Dams jointly with RILEM-ACS


What is AAR?

• AAR– Chemical reaction between hydroxyl ions associated with alkalis sodium and potassium from Portland cement with certain mineral phases in the coarse or fine aggregate.

– Two main types ASR and ACR. The ASR is most common.• ASR (Alkali‐Silica Reaction)

– reaction between alkali hydroxide in Portland cement and certain siliceous rocks such as chert, quartz and volcanic glass in some aggregates.

• ACR (Alkali‐Carbonate Reaction)– reaction between the alkali hydroxides in Portland cement and certain dolomatic limestone aggregates.


Expansion Mechanism ‐ ASR

• Silica minerals unstable in high pH solution• Silica ‐ gels are formed from contact with the Portland

cement• Swelling, by absorption of solution, of the gel

produced at the periphery through the volume and pre‐existing cracksp g

• Swelling of these particles• Application of strong pressures (4 to 6 MPa) on the

cement paste• Causes microcracks in the paste• Results in expansion of the concrete• Expansion rates from 20 to 150 micro‐strain per year


ASR Gel Coating (Reaction Rim) and Crack


ASR Gel Particle


15 September 2009 Robin Charlwood - AAR in Dams & Hydro Projects - Paris 2009

2

ASR Gel Filled Cracks and Air Voids


ASR Effects – Gel Filled Cracks


SEM Analyses of Gel Particle


Conditions Required for AAR

• A Reactive Aggregate– reactive minerals present– aggregate particle size (smaller particle size, greater expansion)– porosity and permeability

• High Hydroxyl and Alkali Ion Content– cement is the major source– alkalis from certain aggregates may contribute

• Sufficient Moisture– threshold moisture content is about 80 to 85 RH– internal humid conditions

• “Warm” Temperature – Reaction rate is temperature dependent


Prevention

• AAR concrete can be prevented by

– the use of a nonreactive aggregate

– keeping cement alkali content below 3.0 kg/m3

Na20 equivalent, or less for highly reactive aggregatesaggregates

– substituting supplementary cementing materials such as

• blast furnace slag

• fly ash

• silica fume


Method of Evaluating Potentially Reactive Aggregates

General procedures

• Field Performance– concrete at least 10 years oldsimilar concrete and environmental conditions– similar concrete and environmental conditions

• Laboratory Investigations– petrographic examination– chemical test – accelerated mortar bar ASTM C1260– concrete prism ASTM C1293



3

Signs of AAR

• Concrete expansion: deformation, extrusion of joint seals, closing of joints, differential movement and gate blockage.

• Surface cracking (map cracking): typically polygonal crackingpolygonal cracking

• Reaction products: ASR generates gels which may exude on the surface of the concrete particularly at joints. The presence of this gel does not necessarily imply AAR.

• Dark reaction rims: visible at the periphery of certain reactive aggregates.


UV Test: Detects Presence of Silica Gel


Effects of AAR

• Mechanical properties are not equally affected. From most to least affected.– Long‐term elastic modulus/creep– direct tensile strengthg– flexural tensile strength– loading and unloading cyclic behavior– compressive strength and splitting tensile strength and bond strength

– sonic wave propagation


Management of AAR‐Affected Structures:

– Inspection Program• periodic visual inspections• sampling and lab testing (petrography, mechanical and expansion tests)

– Instrumentation and monitoring• crack development, evolution (mapping)• deformations (joint meters, extensometers, plumblines inverted or standard

• concrete stress measurement• Reinforcing steel strain measurement

– Structural Evaluation• estimate structure sensitivity to expansion/need for detailed analysis


Remedial Action

• Damage Control– crack repair by grouting or epoxy resin injection (repetitive)

– reduce surface freeze‐thaw effects by coating• Structural Modification

– install anchors or rebar for stability– slot cutting to accommodate expansion– partial replacement (but compatibility?)

• Reaction Control (long term)– surface treatment (membranes/coatings)– Injection (lithium/CO2?)


What to Measure

• The most common measurements undertaken in concrete dams are as follows– displacements– tilts– strains– total stresses– pore pressure– flow– temperature– crack width and depth evolution



4

Instrumentation

• Geodetic– high precision levels– electronic theodolites– electronic distance measuring devices

• Mechanical– invar rod extensometers– multiple borehole extensometers (invar, graphite, fiberglass rods)

– inverted pendulums– suspended plumblines– dial gauge and caliper crack gauges– rebar cutting for strain measurements


Instrumentation

• Electrical– vibrating wire strain gauges– thermocouples and thermistors– inductance gauges and LVDTs– inclinometers– tilt meters– ultrasonic pulse velocity– seismic tomography– borehole cameras

• Pneumatic and Hydraulic– stress cells– piezometers


Borehole Extensometer Results


Concrete Stresses and Strains

• Concrete Stress

– Difficult to “monitor” stress in AAR‐ affected concrete

– Methods availableMethods available

• Overcoring in concrete ‐ use 150 mm diam cores

• Overcoring provides a “snapshot” of the stress condition. Hence, requires repeat in x years or

• Install a stress monitoring device in the overcoring hole but long term stability is of concern


Measured Concrete Stresses


Control of Duration of AAR

• Alkali Source– depletion of alkalis if main supply is from cement– re‐supply of alkalis from aggregates in some cases

• Water Source– relative humidity tests show high values persist– residual moisture is sufficient for long term expansion?

• Reaction Control – reducing pH by injection (lithium/CO2) not feasible– surface treatment (membranes/coatings) very long term?

• Laboratory Testing – tests may indicate current expansion potential– tests cannot quantify residual expansion– alkali content relative to threshold (3.0 kg/m3+/‐?)

• In‐situ Monitoring– long term trend in‐situ is presently most reliable basis



5

Numerical Modeling Objectives

– Illustrate expansion mechanisms in complex structures

• intake and gravity dam structures• powerhouse foundation and equipment• arch dam behavior

– Assess strength of concrete elements• shear strength of draft tube piers, spillway piers, etc.• cracking analyses using reduced concrete tensile strengthcracking analyses using reduced concrete tensile strength• tri‐axial concrete strength assessment

– Forecast future expansion deformation and effects• include cracking and/or sliding and redistribution• estimate project remaining life/operability

– Estimate benefits of slot cutting on• hydraulic gate binding (i.e., pier rebound)• shear stress reduction• mechanical equipment clearances (for example, gate end clearances)

• stay ring stress assessment and effects of slot cutting15 September 2009 25Robin Charlwood

Key Features of AAR Numerical Modeling

• Concrete growth rates vary throughout the structure because– concrete growth expansion rates depend on the stressstress (in all directions)

– concrete growth rate variation due to changes in moisture content and temperature

– time‐dependent, enhanced creep behavior of AAR affected concrete


Some AAR Cases


USBR’s Stewart Mountain Dam


Three US Dams

Three USBR examples of ASR where expansions phave ceased after about 25 to 30 years


Stewart Mountain DamRepairs to crest and thrust block plus vertical anchors to

maintain seismic stability



6

TVA’s Fontana Dam

Over 10 cmUS movement

since 1940

Over 7.5-cm VERTICAL expansion

since 1940

Unit misalignmentproblems in Powerhouse


TVA Drilled Slots in 1970….

ASSR movements have continued at a constant rate for

Shear stress and slot cut

rate for nearly 50 years…


NB Power’s Mactaquac Project….

Dam crest rise of 10 cm

SW gate jamming

Powerhouse substructure crack, unit misalignment and discharge ring ovalling

ASSR strain rates of up to 145 μ-strain/a in most concrete structures for 30 years

Cracking in end pier of intake


Mactaquac Diamond Wire Saw Cutting 1988….


Mactaquac Diamond Wire Saw Cutting 1988….


Mactaquac Powerhouse: ‐ Layout & Instrumentation



7

Mactaquac: Portion of Powerhouse Finite Element Model


Mactaquac Powerhouse: Discharge Ring Ovalling


• Discharge Ring Ovalling– Discharging ring diameter has reduced by about 7 mm across

longitudinal axis of powerhouse.

– Analysis indicates that the discharge ring would rebound about 2 mm at unit 2 if transverse cuts are implemented.

• Stay Vane Stresses

Mactaquac Powerhouse

y– Stresses were measured in the stay vanes in 1994 and relatively large

vertical bending stresses were measured in vanes ‘racked’ downstream

– The FE model correlated well to measured stresses when nonlinear concrete cracking behavior was simulated.

– A concrete tensile strength of 100 psi was assumed.

– The model was used to assess the benefit of cutting the penstock and implementing a joint thereby reducing racking of the stay vanes.


Chambon Dam slot cutting + membrane


Chambon Dam slot cutting + membrane

Carpi membrane reduces uplift and improves stability

The membrane now 20 years old – is it slowing the reaction?


ICOLD Bulletin 79 on AAR 1991



8





ICOLD Bulletin 79 on AAR 1991Bulletin 79 considers three reactions:

1. Alkali-Silica Reaction (ASR) - alkali reaction with amorphous or reactive silica (opal, chalcedony);

2. Alkali-Silica-Silicate Reaction (ASSR) - alkali reaction with silicates caused by reactions in polyphase siliceous aggregates (greywacke,polyphase siliceous aggregates (greywacke, shale, granite, sandstone); and

3. Alkali-Carbonate Reaction (ACR) - alkali reaction with dolomitic carbonates.

Bulletin focuses on ASR and ASSR as “they are more common and more difficult than ACR”


ICOLD Bulletin 79 on AAR 1991ICOLD Bulletin 79 & CSA identify the effects as:

1. Alkali-Silica Reaction (ASR) – forms sodium silicate gels which leads to EXPANSION, CRACKING, EXUDATION OF GEL AND DETERIORATION OF STRUCTURE;

2. Alkali-Silica-Silicate Reaction (ASSR) – “slow/late ASR”a) if alkalis are in excess then a swelling gel is formed leading to

EXPANSION CRACKING EXUDATION OF GEL ANDEXPANSION, CRACKING, EXUDATION OF GEL AND DETERIORATION,

b) if lime is in excess a less expansive gel results in EXPANSION, CRACKING AND DETERIORATION OF STRUCTURE

3. Alkali-Carbonate Reaction (ACR) – forms brucite (Mg(OH)2) without an expansive gel but leads to WEAKENING OF BOND BETWEEN CEMENT PASTE AND AGGREGATES, MICROCRACKING


1992 CANCOLD/CEA 1st International Conference on

AAR inAAR in Hydroelectric

Plants and Dams -Fredericton, NB,

Canada


1992 CANCOLD/CEA 1st International Conference on

AAR in HydroelectricHydroelectric

Plants and Dams -Fredericton, NB,

Canada



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Acres database of over 100 International AAR Cases with significant damage - 1995


Acres’ database of AAR Cases – 1995now at: www.hatchenergy.com/aar


1995 USCOLD 2nd

International Conference inConference in Chattanooga,

TN, USA


1995 USCOLD 2nd

International Conference in Chattanooga,

TN, USA


1995 USCOLD 2nd


TN, USA


1995 USCOLD 2nd


TN, USA



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Some other ASR Cases


Friant Gravity Dam & Spillway - USA

Local expansion into gates


Stolsvatn Multiple Arch Dam - Norway


Stolsvatn Multiple Arch Dam

Epoxy coating of buttresses to protect from cracking and to gprotect internal rebar anchors

May be replaced


Clanwilliam Dam – South Africa


Clanwilliam Dam

Vertical and horizontal offsets at jointsj



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Skarfoss and Tislei Ambersen Dams - Norway


Skarfoss and Tislei Ambersen Dams

Cracking and leakage

Epoxy coating of buttresses


Pedras-Billings Control Structure - Brazil

New unit?

Downstream face deterioration


Warsak Hydro-electric Plant - Pakistan


Warsak Hydro-electric Plant

Draft tube gate clearance problems



Vertical shear offsets at entry of power tunnel penstocks to powerhouse



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Warsak Hydro-electric Plant- Internal Shear Damage



Penstock entry to powerhouse – shear failure


Warsak Hydro-electric Plant Spillway

Gate clearances


Maentwrog Dam Replacement - Wales


Maentwrog Dam


Maentwrog Dam – Core Samples



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David D Terry Lock & Dam USAAn Example of Investigations & Repair


Piers showing gates and trunnion anchors


Pier lower section cracking & repairs

Diagonal cracks going below waterline


Pier upper section

vertical crack


Typical Pier Concrete

5000 psi concrete

3000 psi concrete

5000 psi concrete

3000 psi concrete

Map crackingshowing

ASR expansion


A Typical Pier Elevation

LegendS = Shear ForceT = Tension

0 5 10 feet

EL. 231.0’NormalPool

Radial Gate Seal Plate(Gate not shown)

TrunnionAnchors

TrunnionEL. 243.0’

C.J. EL. 236.0’

C.J. EL. 246.0’

C.J. EL. 256.0’

C.J. EL. 264.0’EL. 266.35’

Tension Crack

ngth

s30

00 p

si

TT

SS

LegendS = Shear ForceT = Tension

0 5 10 feet

EL. 231.0’NormalPool

Radial Gate Seal Plate(Gate not shown)

TrunnionAnchors

TrunnionEL. 243.0’

C.J. EL. 236.0’

C.J. EL. 246.0’

C.J. EL. 256.0’

C.J. EL. 264.0’EL. 266.35’

Tension Crack

ngth

s30

00 p

si

TT

SSPool

C.J. EL. 226.0’

C.J. EL. 216.0’

EL. 293.10’EL. 291.0’

1

10

61’ - 6”

T.W.L.

C.J. EL. 206.0’

Shear Crack

Norm

al C

oncr

ete

Stre

n50

00 p

si30

00 p

si

T

T

SS

T

T

Pool

C.J. EL. 226.0’

C.J. EL. 216.0’

EL. 293.10’EL. 291.0’

1

10

61’ - 6”

T.W.L.

C.J. EL. 206.0’

Shear Crack

Norm

al C

oncr

ete

Stre

n50

00 p

si30

00 p

si

T

T

SS

T

T



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Reinforcing Steel In‐Situ Strain Testing


Reinforcing Steel In‐Situ Strain Testing• The results from tests in the 5000 psi concrete in indicated an accumulated expansion of approximately 1000 micro‐strain in both vertical and horizontal directions.

• The results from test in the 3000 psi concrete above the lift joint showed

bl h i t l i b blcomparable horizontal expansion probably due to it moving intact with the 5000 psi concrete .

• These results confirm crack mapping estimates of expansion in the 5000 psi concrete.

• The results for the 3000 psi concrete are variable but do not contradict the underlying mechanism hypothesis.15 September 2009 80Robin Charlwood

Concrete Core Testing• Six concrete cores were taken from piers 8 and 16, one

from the 5000 psi concrete in each pier, one from the 3000 psi concrete below the El. 216 lift joint in each pier and one from the 3000 psi concrete above the El. 236 lift joint.

• These samples were taken by local contractor and shipped for petrographic analysis and the effects of ASR

• Dr. Grattan‐Bellew’s work included:

‐ determination of damage rating indices (DRI),

‐ petrographic analyses,

‐ pulse velocity measurements, and

‐ free alkali tests.


Concrete Core Testing Results • The Damage Rating Index is a measure of the extent of expansion and chemical deterioration that has occurred to date based on visual microscope examination of thin sections.

• A DRI value greater than 30 normally indicates significant ASR.

• These analyses showed DRI values of 84 in 5000 psi concrete. These are consistent with the strain measurement results.

• The values for all the samples from 3000 psi concrete all showed DRI values less than 30, as expected.15 September 2009 82Robin Charlwood

Concrete Core Testing Results

• Pulse velocity measurements showed values of 4.6 and 4.2 km/s for the more expanded 5000 psi concrete and slightly higher values of from 4.6 to 5.3 km/s for the 3000 psi concrete. These values correspond to compressive strengths in the range of 4200 to 5600 psito 5600 psi.

• Petrographic analyses on thin sections found chert, which contains micro‐crystaline quartz, and chalcedony, both potentially reactive minerals. There were variable signs of fly ash but apparently it was not in sufficient quantities to prevent ASR.15 September 2009 83Robin Charlwood

Concrete Core Testing Results • Free alkali content tests were performed to assess the

potential for continuation of the reaction. A value > 2.0 kg/m3 is normally sufficient to allow the reaction to proceed.

• The values were generally low and this was attributed to the possible presence of fly ash.

• There was some consistency with other observations in the 5000 psi concrete which showed a high free alkali value of5000 psi concrete which showed a high free alkali value of 2.5.

• The 3000 psi concrete above El. 236 showed a value of 2.0 and the concrete below El. 216 showed a low value of 1.2 which suggested little or no ASR there.

• The results at pier 8 all were above 2.0 although other data suggests little expansion has taken place to date in the 3000 psi concrete there.



15

GROW3D & Horizontal Rebar Stress Results


Trunnion Anchor Stress Results

• The additional stress in the trunnion anchors is in the order of 11,000 psi

• This estimate was based on the GROW3D model

• ASR growth relation that reduces the rate f i ith i i iof expansion with increasing compressive

stress. • This increment in not considered sufficient to require action to de‐stress these anchors at this time.

• If the expansion continues this will increase and some means to monitor this stress build up may be required.15 September 2009 86Robin Charlwood

Upgrade Concept

#11 dowels


Grouting anchors from the platform

Exploratory borehole& Extensometer hole

# 11 bar


CONCLUSIONS

• The approach taken at Terry Lock and Dam to address ASR damage to piers appears to have been successful in that the future life of the spillway can be extended at modest cost.

• As a result of the inspections, testing and analyses we now know more about the distribution and mechanisms of ASR growth at the facility and are able to implement a repair that will stabilize the piers that are most p pdamaged.

• It is likely, but not certain, that additional significant ASR expansion may occur in the future.

• The extensometers installed as part of the repairs will provide a means for monitoring differential expansions over time as a basis for assessing the condition of the piers in the future and assist in decisions regarding any further grouting or other repairs


Arch Dams



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Gene Wash and Copper Basin Dams (Hill)

• Background– Gene Wash arch dam is 40 m high with a crest length of 131 m (incl.

thrust block)

– Copper Basin arch dam is 57 m high with a crest length of 77 m

– Operated by Met Water District of South California

– Notable features are relatively wide cracks on d/s face near abutments


Tension stresses

Vertical growth

Tension stresses

stresses


Gene Wash and Copper Basin Dams (Hill)

• Deformations– Gene Wash

• 1942 to 1965 dam height increased by about 90 mm due to AAR (100 µε/yr)

• 1965 to 1995 dam height increased by only 8 mm• 1965 to 1995 dam height increased by only 8 mm

• upstream deflection of 110 mm from 1942 to 1965 then ceased

– Copper Basin• very similar movements to those measured at Gene Wash Dam


Cahora ‐ Bassa Dam (Ramos et al)

• Background– double curvature arch dam constructed between 1971 and 1974 in Mozambique

– height of 170 m and a crest length of 300 m

– expansion detected using no‐stress strain meters and through petrographic evaluation


Cahora‐Bassa Dam (Ramos et al)

• Deformations– concrete expansion was detected in 1979

– low rates of expansion measured, in the range of 13 t 26 /13 to 26 µε/yr

– recent measurements from precise levels show about 6 µε/yr

– larger measured expansion strains at the quarter points (M‐pattern)


Cahorra Bassa ‐Mozambique

15 September 2009 Robin Charlwood 96


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Santa Luzia and Alto‐Ceira Dams

• Santa Luzia Dam– 76 m high cylindrical arch dam in Portugal

– 50 mm of vertical expansion and 30 mm translation upstream

– vertical displacement form an ‘M’ pattern

Alto‐Ceira Dam– a total expansion of 1600 µe or 40 µe/yr has accumulated

– considering replacing the dam!


Fontana Dam – Emergency Arch Dam Spillway

Approx 30 cm downstream movement


Fontana Emergency Spillway Arch Dam (Yeh et al)

• 17 m high single curvature arch dam operated by TVA

• crest has moved over 400 mm upstream

• Simple linear FEA could not match measured stresses or thermal movements


Kouga Dam, South Africa (Elges et al)

• Background– 78 m high arch dam with a 317 m crest length completed in 1969

– operated by Department of Water Affairs, South fAfrica

– concrete expansion detected in 1976 and rate of expansion has been reducing since 1984

– largest horizontal displacement changes occur near the quarter points (M‐pattern)


Kouga Arch Dam (Elges et al)


Kouga Dam, South Africa(Elges et al)

• Analysis Performed– Elges et al report using linear elastic FEA and modeling AAR as equivalent temperature load

th l i i di t d t i d l l d– the analysis indicated tension under normal loads at the upstream heel area (without AAR)

– the analysis with AAR loads found tensile stresses up to 5 MPa which was deemed unrealistic although displacements were in agreement with observed values



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Conclusion from Arch Dam Case Reviews

• AAR effects in arch dams tend to cause diagonal cracks semi‐parallel to abutment contact which raises stability questions

• Deformations patterns are similar with large upstream movement and “M” shape

• Analysis of AAR affected arch dams using linear FEA and• Analysis of AAR‐affected arch dams using linear FEA and equivalent thermal expansion has been unsuccessful

• the lack of correlation between FEA and measured behavior leads to uncertainty in the condition of the dam

• the need for remedial measures and their design is difficult to determine because the state of stress is not known


Key Modeling Needsfor AAR in Arch Dams

• Stress variations are quite large through the thickness of an arch dam hence the stress‐dependent nature of AAR expansion is very important

i f l t (h l ) th t f i ill b• in areas of low stress (heel area), the rate of expansion will be relatively high tending to cause compression where tension might otherwise occur

• arch dams are typically thin efficient concrete structures implying relatively large compression stress conditions, therefore creep strains become important to offset AAR‐effects.


Demonstration Analysis Using GROW3D

• dam shape and properties similar to Kouga arch dam

• dam height is 80 m with a 300 m crest

• 20‐noded hexahedron and 15‐noded wedge elements used in dam and foundation


Demonstration Analysis Finite Element Mesh


Demonstration Analysis Demonstration Analysis Plan and coordinatesPlan and coordinates


Demonstration AnalysisDemonstration Analysis



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Demonstration Analysis Using GROW3D

• initial strains loads due to concrete expansion are computed at integration points using stress dependant concrete growth load and three principal stresses

• the following constants define the concrete growth law:• the following constants define the concrete growth law:

• εgo = 33 µε/yr; σo = 0.3 MPa; K = 27

ε εσσgi go

i

ot t K( ) ( ) log= −

⎛⎝⎜

⎞⎠⎟

⎡

⎣⎢

⎤

⎦⎥


Summary of Results• The observed ‘M’ pattern of horizontal displacements was

reproduced by the model

• Generally small changes in arch stresses due to AAR were computed. Thus the dam is relatively flexible and does not restrain the expansion.

• The cantilever stresses show increased compression on the upstream face and reduced compression on the downstream face

• Some tensile stresses develop on the downstream face near the upper abutments


Conclusions

• The stress dependent and creep effects in AAR‐affected concrete must be modeled to avoid unrealistic tensile stresses.

• The cantilever compressive stresses tend to reduce overThe cantilever compressive stresses tend to reduce over time on the d/s face where under normal loads a strong compression field exists

• On Kouga dam the upstream face initially had some tension under normal loads and AAR induced compression in these areas. This compressive stress increased on the u/s face.


Case History of GROW3D Use:US Arch Dam

• Contracted to review data and perform GROW3D finite element analysis of arch dam

• 300 ft high arch damg• Constructed in 1930’s• In 1950’s signs of AAR noted• Diagonal cracks at abutments• Concrete strength and durability is being affected by AAR


US Arch Dam

Diagonal cracks on left abut

Diagonal cracks on right abut

left abut


Arch Dam: D/S FaceLeft Abutment: Diagonal Cracks



20

Arch Dam: D/s FaceRight Abutment


Arch Dam: FEA MeshGROW3D Stress Analysis


Arch Dam: Stress FlowNormal Loading: No AAR


Arch Dam: Stress FlowAAR Effects Included at t = 56 yrs


Arch Dam: AAR StressesMaximum Tensile Stresses


Arch Dam: Compressive Strength



21

Arch Dam: GeophysicsSeismic Tomography Results


Summary of Results• AAR growth in the center monoliths tends to cause diagonal

shear stresses on the downstream face

• The cantilever compressive stresses tend to reduce over time on the downstream face where under normal loads a strong compression field exists

• AAR growth will tend to be higher on the upstream face due to low arch compression thereby possibly limiting the propagation of diagonal cracks from the downstream face.

• The cantilever compressive stress increased on the upstream face tending to offset tensile stresses at the heel.


Conclusions

• The stress dependent and creep effects in AAR‐affected concrete must be modeled to avoid unrealistic tensile stresses.

• The modeling results appear to correlate with some limited seismic tomography data

• Insitu stress measurements are being collected to check the stress distribution predictions

• If these results are in fact correct then dam safety concerns are reduced


Granada Workshop• There were a number of very interesting

cases reported from around the world• Presentations are on the web at:

http://www.dam-research.org/Granada-2007/index.html

I ll t f h t id d• In some, small rates of what were considered ASR expansion were causing serious problems

• There were several cases of Internal Sulphate Attack reported

• Samples…


Granada Workshop ProgramThursday, October 188:30 a.m. – 10:30 a.m. Session 1: Introduction and

Objectives 10:50 a.m. – 12:30 p.m. Session 2: Chemical Reactions and

Processes 1:30 p.m. – 3:50 pm Session 3: Case Histories 4:10 p.m. – 6:10 p.m. Session 4: Numerical Modelling

Friday, October 19

8:30 p.m. - 10:30 p.m Informal No-Host Reception/Dinner 8:30 a.m. – 10:30 a.m. Session 5: Remedial Actions &

Prevention 11:00 a.m. – 12:30 p.m. Session 6: Panel Discussion –

Lessons learned


Spanish cases – Arturo Gil

Affected structures that are known or suspected of being affected:

12 dams3 gravity1 arch-gravity3 buttress5 arch

1 spillway3 intakes2 canals2 hydroelectric

power stations

Siliceous terraneCalcareous terraneClayey terrane15 September 2009 126Robin Charlwood


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Main types of reactions

Materials- Siliceous aggregates- Portland cements. Some with small addition of pozzolanic material

Main reagents and resulting products in presence of H2O

Cao, MgO in cement

Expansive hydration

Sulphates Ettringite

Expansive gels

Massive presence of Ca(OH)2 in paste

Decisive in most reactions

Cement paste

+

Crystalline silica

Alkalis from the cement or

aggregates

+

in cement y

Sulphides in aggregates


San Esteban dam


Surface of sample showing high porosity


STRUCTURAL REHABILITATION AND WATERPROOFING

Main jobs performed:

Injection in defective lift joints

Facing of the upstream face


15 September 2009 131Robin Charlwood 15 September 2009 132Robin Charlwood


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KW

E

KRAKWWB

KWBZ

HKB

KR

SK

WA

RK

S RA

DA

G

RK

RA

WA

G

AKW

LöntschKSL

LKW

KW

S

ER

AG

KWF

Rüchlig

RK

N

Some Swiss Dams – Bastian Otto, NOK

KLL

KSL

KVRKWI

KWZ KHR

Ofible

Ofima

Aegina EM

FMM

Lienne

GD

Argessa

OIM

LMSA KWM

ELIN

CAL

ALK EKW

KWF

GöschenenWassen

TEC

Patvag

Isola

Bernina NordScala

Illsee

Serra


3

321 4 5 6 7 8 9 10

0

Block number

Isola Dam

Hydraulische Energie

5

57 6 6 6 6 7Number of cracks

Zone with cracks

15 September 2009Robin Charlwood


24

lake level

summer

full lake

1988

2004


radial crestdisplacement

radial displacementat control gallery

upstream


observationswelling of the upper sectionin vertical direction 0.02%

calculationvolume increase by 0.02%horizontal stress of 6 MPa

1960 to 200545 years


observationswelling of the lower sectionin vertical direction 0.005%

observationmean concretetemperature 7 °C

15 September 2009Robin Charlwood

Workshop Panel Questions A - IMPORTANT REACTIONS:1. What are the important chemical reactions? Causes, interactions,

mechanisms, effects?2. Options for diagnosis and testing in new & existing structures?

B - CONTROL & MANAGEMENT:3. Effectiveness of control or management in affected structures? 4. Remaining or residual expansion strains and deterioration?

C - MODELLING & MONITORING:5. Can the available numerical models treat all the important reactions?6 Can existing models reliably forecast future behaviour of existing structures?6. Can existing models reliably forecast future behaviour of existing structures?7. What instrumentation and testing for modelling and monitoring?

D - PREVENTION & REMEDIATION:8. Options for and efficacy of remediations in existing structures?9. Effectiveness of prevention in new structures?10. What are effective laboratory criteria for prevention by testing?11. How big can be an expansion can be tolerated for a mass concrete element

or structures? In terms of μstrains? Or Cracks openings?

E - RESEARCH & DEVELOPMENT:12. R & D needs including controlled prototype testing?


Panel Responses – Lessons LearnedA - IMPORTANT REACTIONS:1. What are the important chemical reactions? Causes, interactions,

mechanisms, effects?RESPONSES:1. The most important chemical reactions are alkali aggregate reactions with

siliceous aggregates, this affects up to 30% of dams in some countries. 2. A more minor reaction is of aggregates containing sulfide minerals (e.g.

pyrite) which may oxidize to sulfate leading to internal sulfate attack. This is reported in a handful of cases.

3. Although massive deposits of ettringite have also been observed, these are a common feature of old concrete (especially when saturated) and degradation due to delayed ettringite formation is very unlikely as this occurs only when the temperature during hydration exceeds 70°C (on a conservative basis) and more realistically 80 or 90°C.

Q: To what extent can these various reactions co-exist?


Panel Responses – Lessons LearnedA - IMPORTANT REACTIONS:2. Options for diagnosis and testing in new & existing structures?RESPONSES:1. In the case of new structures, it is a matter of assessing materials and

mix combinations in advance, to ensure an absence of potentially expansive reactions.

2. Dams require long term tests well in advance of construction. 3. RILEM has published guidance on assessing aggregate combinations

for AAR potential and is now developing a practicable and universally reliable performance test; it will be important to ensure its applicability to dam structures.

4. RILEM is also preparing guidance on the diagnosis of AAR in existing structures, stressing the key value of experienced petrographic examination of suitable samples, which can also identify other deteriorative mechanisms.

5. Further guidance is also planned for the appraisal of affected structures, including tests to assess any residual potential for continued expansion; again it will be essential to ensure that the guidance makes allowance for the special circumstances of large concrete dams.

18/19 October 2007 Robin Charlwood & Juan Manuel Buil Sanz 14315 September 2009 143Robin Charlwood

Panel Responses – Lessons LearnedB - CONTROL & MANAGEMENT:3. Effectiveness of control or management in affected structures? RESPONSES:1. At this time there is no known intervention method to curtail or stop the

expansive reactions within the concrete mass, either ASR, ACR or ISA.2. Lithium salts injection has been suggested in lab tests but it is not feasible to

get uniform distribution in large dams3. In some ASR cases the reactions have ceased after about 30 years. What

about ACR or ISA?4. Some dams have been waterproofed with upstream membranes. It is not yet

known if this will significantly reduce the expansive reactions. 5. Chambon Dam has geo-membrane upstream for the top 60 m for 20 years

but there are still other moisture access paths available.6. San Esteban Dam also coated with geo-membrane Q: Long term (maybe 30 years?) observations may provide indications of the

effects but a carefully controlled prototype experiment is required to derive reliable results.



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Panel Responses – Lessons LearnedB - CONTROL & MANAGEMENT:4. Remaining or residual expansion strains and deterioration?RESPONSES:1. Reports indicate that structural problems may occur in dams with expansions

as low at 0.01% (0.1mm/m). 2. Such low levels of expansion are general regarded as below the threshold for

deleterious effects in most test methods and at this stage the signs of ASR in petrographic analysis may be difficult to detect.

3. Similarly most cases of expansion reported appeared to initiate after several decades and to be advancing at a linear rate with no sign of leveling off.

4. Such results are likely to be quite variable because of the large aggregate size (some areas contain a lot of aggregate others less).

5. In terms of kinetics, there is considerable evidence that this follows the Arrhenius law (R=Roexp(-Ea/RT))with increasing temperature and the activation energy seems to be fairly constant in reported studies, so extrapolation to lower temperatures should be fairly reliable.

Q: Can residual expansion can be measured on cores taken from the structure if care is taken to avoid leaching (J.Wood recommends conserving in sealed container with a small amount of water)?


Panel Responses – Lessons LearnedC - MODELLING & MONITORING:5. Can the available numerical models treat all the important reactions?RESPONSES:1. Most previous models were simply mechanical expansion models and if they

were calibrated based on deformations and stresses, then the type of reaction was not considered an issue.

2. Newer kinetic models include explicit relations regarding temperature and moisture. In theory these will require recalibration for each case of each reaction type.

3. It is possible that the extent of enhanced creep will vary depending on the damage effects of the particular reaction type

4. Similarly stress-dependency of the expansion may be related to the driving mechanism and therefore reaction type specific

Q: This topic requires further investigation.


Panel Responses – Lessons LearnedC - MODELLING & MONITORING:6. Can existing models reliably forecast future behaviour of existing structures?RESPONSES:1. Historically, “heuristic” models (such as GROW3D and CANT) developed in the 80’s

and 90’s have met a pressing need of industry.2. We are all indebted to the excellent experimental research program on AAR undertaken

in France by the LCPC (Larive, Multon, Toutlemonde) which cast the problematic of AAR into a formalism rooted in Chemistry, Thermodynamics, and Mechanics.

3. As a result of this work, there are a number of codes based on this model developed in France (LRPC/CESAR/Seignol, EdF/Grimal), and US (Colorado/Merlin/Saouma). ( g ) ( )However, these models are more complex, and certainly more accurate, than the current ones widely used in practice. They are being adopted in Europe and Japan.

4. Practically any Finite Element code has sufficient number of “parameters” which can be fine-tuned to give numerical results which appear to match experimental observations. Great care is required on calibrating the model before forecasting.

Q: We should design a test of uniqueness of calibration and reliability for forecasts. Maybe an ICOLD Numerical Methods Benchmark Topic where models are calibrated for an existing condition and future forecasts are compared?


Panel Responses – Lessons LearnedC - MODELLING & MONITORING:7. What instrumentation and testing for modelling and monitoring?RESPONSES:1. Mechanical models require “free” and “restrained” expansion rates as inputs.

Measurements of vertical expansion provide a reasonable approximation to “free” expansion.

2. Longitudinal strain rates on affected structures are required and are the most reliable inputs.

3. To determine expansion rates at least three years of high accuracy data are required to allow the trend to be filtered from the cyclic data.

4. Deformation data accuracy of about 1 με/year is required5. In-situ stress measurements are required to calibrate a model. Accuracy is

usually limited to about 0.7 MPa (100psi) but is sufficient.6. Offsets at cracks or construction joints are very valuable. Accuracy of about

0.5 mm/year is required.7. RH is not a reliable indicator of water supply for the reaction. 8. Need stress dependency of expansion and enhanced creep parameters Q: Need alternative measure of available moisture. Degree of saturation?


Panel Responses – Lessons LearnedD - PREVENTION & REMEDIATION:8. Options for and efficacy of remediations in existing structures?RESPONSES:1. Options for remediation depend upon the impacts of the expansion on the

structure and associated equipment.2. In some cases continued monitoring suffices, whereas in other examples

some sort of protection, strengthening, or actions such as slot cutting to accommodate movement or partial replacement might be necessary.

3. Affected structures can usually be managed and AAR has rarely, only about 4 known cases, been the sole cause of actual failure.

4. In dams and related water-retaining construction, complete exclusion of water is not feasible and water-resistant coatings can sometimes cause new problems for concrete rather than having a beneficial effect.

5. RILEM is preparing guidance on appraisal and management of structures affected by AAR.

Q: Is this going to be relevant to dams?


Panel Responses – Lessons LearnedD - PREVENTION & REMEDIATION:9. Effectiveness of prevention in new structures?RESPONSES:1. There is extensive knowledge about ASR and various forms of expansive

sulfate action, so that prevention ought to be effective when materials and mixes have been adequately assessed in advance and these are then properly monitored during construction.

2. Carbonate aggregates need more research and RILEM is presently conducting a review; it is thought possible that, in at least many cases,

i tl i t d ith b t t i ht bexpansion apparently associated with carbonate aggregates might be a special case of ASR. RILEM has established that many of the preventative measures that are usually effective at controlling conventional ASR are not similarly reliable in the case of expansion associated with carbonate aggregates.



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Panel Responses – Lessons LearnedD - PREVENTION & REMEDIATION:10. What are effective laboratory criteria for prevention by testing?RESPONSES:1. RILEM has devised a scheme - AAR-0 - for assessing aggregate

combinations for AAR potential, including petrographic assessment, screening tests and dependable concrete expansion tests, with one version - AAR-4 -being capable of interpretation after just 3 or 4 months and therefore practically useful for projects.

2. Criteria have been tentatively suggested in AAR-0, but these might need to be i d i t f l d RILEM h l d ft d i t ti lreviewed in respect of large dams. RILEM has also drafted an international

specification - AAR-7 - which assesses the level of precaution required on the basis of structure type and environment, with dams falling into the highest risk category, and then provides a menu of prevention measures.

Q: However, the current criteria in AAR-7 might need to be reconsidered for large dam structures.


Panel Responses – Lessons LearnedD - PREVENTION & REMEDIATION:11. How big can be an expansion can be tolerated for a mass concrete element

or structures? In terms of μstrain? or crack openings? or..?RESPONSES:1. Tolerable accumulated expansion depends on the dam configuration, size,

function (incl water access etc) and time frame (100 years +)2. Some recent cases in Switzerland with very wide mild curvature gravity

arches show serious issues with only 100 μstrain free expansion3. In other cases the expansion is restrained expansion of much larger

values of “free expansion” can be accommodated


Panel Responses – Lessons LearnedE - RESEARCH & DEVELOPMENT:12. R & D needs including controlled prototype testing?RESPONSES:1. Understanding of slow expansion mechanisms with low alkali content (eg dam

with <1 kg/m3 free alkali and 20 – 50 μstrain/year!!)2. Clarification of potential interactions or co-existence of different expansion

reactions (ASR, ACR, ISA, DEF and ??)3. Techniques for estimating remaining expansion in existing dams4. Understanding of indefinitely continuing expansion mechanisms (alkali

“resupply” from aggregates etc)pp y gg g )5. A large scale, very long term, prototype test of a sealed dam to examine

effectiveness of sealing??6. Material properties:

a) Clarify volumetric vs anisotropic expansion mechanismsb) Need creep parameters for expanding concretec) Need to know stress dependency of expansiond) Effects of global and local temperature fieldse) Dependency on water, RH, degree of saturation, …

7. Modeling reliability – test use of “calibrated” models for forecasts

18/19 October 2007 Robin Charlwood & Juan Manuel Buil Sanz 15315 September 2009 153Robin Charlwood

Panel Responses – Lessons Learned

Workshop PPTs are at:http://www.dam-research.org/Granada-2007/index.html

hosted by Victor Saouma at University of Colorado in Boulder


ICOLD Bulletin Contents1. Nature and Extent of the Problem2. Chemical reaction causes, factors (at micro level)3. Physical Effects and Factors for Each Reaction Type

(at meso and macro level)4. Diagnosis5. Mathematical modelling6 Management Options6. Management Options7. Prevention 8. Conclusions and Recommendations

• Appendices: • A – A Model Investigation Program• B - Case Histories


Panel Questions – Lessons LearnedA - IMPORTANT REACTIONS:1. What are the important chemical reactions? Causes, interactions,

mechanisms, effects?2. Options for diagnosis and testing in new & existing structures?

B - CONTROL & MANAGEMENT:3. Effectiveness of control or management in affected structures? 4. Remaining or residual expansion strains and deterioration?

C - MODELLING & MONITORING:5. Can the available numerical models treat all the important reactions?6 Can existing models reliably forecast future behaviour of existing structures?6. Can existing models reliably forecast future behaviour of existing structures?7. What instrumentation and testing for modelling and monitoring?

D - PREVENTION & REMEDIATION:8. Options for and efficacy of remediations in existing structures?9. Effectiveness of prevention in new structures?10. What are effective laboratory criteria for prevention by testing?11. How big can be an expansion can be tolerated for a mass concrete element

or structures? In terms of μstrains? Or Cracks openings?

E - RESEARCH & DEVELOPMENT:12. R & D needs including controlled prototype testing?



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Thank you for your attention

15 September 2009 Robin Charlwood 157


Documents

Some Dam AAR Milestones…. AAR in Dams and Hydroelectric Plantscivil.colorado.edu/~saouma/AAR/Library/Paris-2009/01-Charlwood.pdf · AAR in Dams and Hydroelectric Plants Robin G