1. ASU/ACS/99 A Concrete Arch Dam in Arizona (USA) §Stewart Mountain Dam l Deterioration of Dam l Analysis: Unsafe under Earthquake load l Measures: Complete replacement Epoxy coated Post-tensioning

2. ASU/ACS/99 Analysis §Loads considered l Gravity l Hydrostatic Pressure l Temperature l Seismic §Joint element incorporated §Collision between elements modeled §Analysis accounts for additional flexibility provided by non-linear joints

3. ASU/ACS/99 Alkali Silica Reaction §Reaction of Aggregates with Cement §Causes Extensive Cracking and Fragmentation §Extensive testing is performed

4. ASU/ACS/99 Results of testing analysis §Interior concrete was still strong §No further deterioration due to ASR expected §Total replacement is not required §Epoxy coated Post-tensioning l Best remedy for seismic safety l Least expensive l Used 62 cables, 22 wire 15.24mm diameter

5. ASU/ACS/99 Modeling of the joint elements §Three Dimensional Element §Account for the following effects l Friction l Loss of contact between different pours l Impact between disjointed elements l Loss of joint material

6. ASU/ACS/99 Joint types §Shear component of the joint force l force is in the joint plane l determined by frictional interaction §Normal component §No inertial properties §Nonlinear (Piecewise linear) force- displacement relationship

7. ASU/ACS/99 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

8. ASU/ACS/99 Chemistry of Alkali Silica Reaction §Cement production involves raw materials that contain alkalis in the range of 0.2 to 1.5 percent of Na 2 O §This generates a pore fluid with high pH (12.5 to 13.5) §Strong alkalinity causes the acidic siliceous material to react

9. ASU/ACS/99 ASTM specification §ASTM C150 designates cements with more than 0.6 percent of Na 2 O 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/m 3, alkali-silica reactions will not occur

10. ASU/ACS/99 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 l alkaline admixtures l aggregates that are contaminated l penetration of seawater l deicing solutions

11. ASU/ACS/99 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

12. ASU/ACS/99 Case Histories §Buck Hydroelectric plant on New River (Virginia, US) §Arch dam in California l crown deflection of 127 mm in 9 years §Railroad Canyon Dam §Morrow Point Dam, Colorado, USA §Stewart Mountain Dam, Arizona §Parker Dam (Arizona) l expansion in excess of 0.1 percent

13. ASU/ACS/99 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

14. ASU/ACS/99 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)

15. ASU/ACS/99 International Congress Creating With Concrete 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: University of Dundee Dundee, Scotland, UK

16. ASU/ACS/99 REHABILITATION AND RETROFITTING OF AN ARCH DAM By Dr. Avinash C. Singhal Arizona State University Tempe, Arizona, USA

17. ASU/ACS/99 Overview §Introduction §Alkali-Silica reaction and its effects §Seismic Study §Case Study: Stewart Mountain Dam l Problems encountered l Remedial measures l Analysis l Post-tensioning of dam structure

18. ASU/ACS/99 Dam deterioration §Bond within dam structure was not intact l Caused due to formation of laitance l Cleaning of horizontal construction surfaces was not recognized l 13 out of 16 joints unbonded (core-drilling) §Alkali-silica reaction was not recognized §Local seismicity was unknown

19. ASU/ACS/99 §Located fifty miles east of Phoenix, Arizona on the Salt River §Double curvature arch dam l 64.6 m high l 2.44 m thick across the crest l 10.36 m thick across the base l 177.7 m long along the crest Stewart Mountain Dam