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A Concrete Arch Dam in Arizona (USA). Stewart Mountain Dam Deterioration of Dam Analysis: Unsafe under Earthquake load Measures: Complete replacement Epoxy coated Post-tensioning. Analysis. Loads considered Gravity Hydrostatic Pressure Temperature Seismic Joint element incorporated

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a concrete arch dam in arizona usa
A Concrete Arch Dam in Arizona (USA)
  • Stewart Mountain Dam
    • Deterioration of Dam
    • Analysis: Unsafe under Earthquake load
    • Measures:
      • Complete replacement
      • Epoxy coated Post-tensioning

ASU/ACS/99

analysis
Analysis
  • Loads considered
    • Gravity
    • Hydrostatic Pressure
    • Temperature
    • Seismic
  • Joint element incorporated
  • Collision between elements modeled
  • Analysis accounts for additional flexibility provided by non-linear joints

ASU/ACS/99

alkali silica reaction
Alkali Silica Reaction
  • Reaction of Aggregates with Cement
  • Causes Extensive Cracking and Fragmentation
  • Extensive testing is performed

ASU/ACS/99

results of testing analysis
Resultsof testing analysis
  • Interior concrete was still strong
  • No further deterioration due to ASR expected
  • Total replacement is not required
  • Epoxy coated Post-tensioning
    • Best remedy for seismic safety
    • Least expensive
    • Used 62 cables, 22 wire 15.24mm diameter

ASU/ACS/99

modeling of the joint elements
Modeling of the joint elements
  • Three Dimensional Element
  • Account for the following effects
    • Friction
    • Loss of contact between different pours
    • Impact between disjointed elements
    • Loss of joint material

ASU/ACS/99

joint types
Joint types
  • Shear component of the joint force
    • force is in the joint plane
    • determined by frictional interaction
  • Normal component
  • No inertial properties
  • Nonlinear (Piecewise linear) force-displacement relationship

ASU/ACS/99

alkali silica reaction1
Alkali Silica Reaction
  • Reaction of alkali ions present in Portland Cement and siliceous material in aggregates in the presence on hydroxyl ions
  • Leads to expansion, cracking, loss of strength, durability and elasticity
  • Cause of distress for structures exposed to humid environment

ASU/ACS/99

chemistry of alkali silica reaction
Chemistry of Alkali Silica Reaction
  • Cement production involves raw materials that contain alkalis in the range of 0.2 to 1.5 percent of Na2O
  • This generates a pore fluid with high pH (12.5 to 13.5)
  • Strong alkalinity causes the acidic siliceous material to react

ASU/ACS/99

astm specification
ASTM specification
  • ASTM C150 designates cements with more than 0.6 percent of Na2O as high-alkali cements
  • Even with low alkali content, but sufficient amount of cement, alkali-silica reactions can occur
  • Investigations show that if total alkali content is less than 3 kg/m3, alkali-silica reactions will not occur

ASU/ACS/99

contribution of calcium hydroxide
Contribution of Calcium Hydroxide
  • Ca(OH)2 is present in sizable proportions in cement
  • Even if alkali content is small, there is a chance of alkali-silica reaction due to
    • alkaline admixtures
    • aggregates that are contaminated
    • penetration of seawater
    • deicing solutions

ASU/ACS/99

expansion mechanism
Expansion Mechanism
  • Breakdown of the silica structure by hydroxyl ions
  • Adsorption of alkali ions on new product
  • This alkali-silicate gel swells in presence of water through the process of osmosis

ASU/ACS/99

case histories
Case Histories
  • Buck Hydroelectric plant on New River (Virginia, US)
  • Arch dam in California
    • crown deflection of 127 mm in 9 years
  • Railroad Canyon Dam
  • Morrow Point Dam, Colorado, USA
  • Stewart Mountain Dam, Arizona
  • Parker Dam (Arizona)
    • expansion in excess of 0.1 percent

ASU/ACS/99

factors influencing the reaction
Factors influencing the reaction
  • Alkali content of cement and other sources
  • Amount, size and reactivity of alkali-reactive material present in aggregate
  • Availability of moisture
  • Ambient temperature
  • Expansive effects of MgO and CaO

ASU/ACS/99

measures for prevention
Measures for prevention
  • Low alkali content cement and mildly reactive aggregate
  • Sweetening of aggregate using limestone
  • Control of access of water to concrete
  • Replacing part of cement by pozzolanic admixtures
  • MgO content should not exceed 6 percent (ASTM C 150-83)

ASU/ACS/99

slide15

Concrete Durability and Repair Technology

Repair Materials and Methods

Thursday 9 September, 1999; 14:00-17:30

G.G.T. Masterton and M. Walker

Conference 5:

Theme 4:

Date:

Chair:

International Congress

Creating With Concrete

University of Dundee

Dundee, Scotland, UK

ASU/ACS/99

slide16
REHABILITATION AND RETROFITTING OF AN ARCH DAM

By

Dr. Avinash C. Singhal

Arizona State University

Tempe, Arizona, USA

ASU/ACS/99

overview
Overview
  • Introduction
  • Alkali-Silica reaction and its effects
  • Seismic Study
  • Case Study: Stewart Mountain Dam
    • Problems encountered
    • Remedial measures
    • Analysis
    • Post-tensioning of dam structure

ASU/ACS/99

dam deterioration
Dam deterioration
  • Bond within dam structure was not intact
    • Caused due to formation of laitance
    • Cleaning of horizontal construction surfaces was not recognized
    • 13 out of 16 joints unbonded (core-drilling)
  • Alkali-silica reaction was not recognized
  • Local seismicity was unknown

ASU/ACS/99

stewart mountain dam
Stewart Mountain Dam
  • Located fifty miles east of Phoenix, Arizona on the Salt River
  • Double curvature arch dam
    • 64.6 m high
    • 2.44 m thick across the crest
    • 10.36 m thick across the base
    • 177.7 m long along the crest

ASU/ACS/99