Hoover Dam Bypass Bridge

Hoover Dam Bypass Bridge

• Concrete arch bridge
• 1,900 feet long
• Concrete arch – 1,000 feet
• Pier caps are 7’ wide x 10’ deep x72’ long

Fire Damage

• Fire Damage to east pier
• Welding on top of pier cap
• Sparks caused form work to smolder
• Formwork smolder over weekend
• Fire damage to underside of pier cap

Repair MethodGoal:

Achieve a durable repair

• Remove damaged concrete using chipping hammers & hydrodemolition
• Perform final preparation using hydrodemolition
• Place new concrete using shotcrete method

Hydrodemolition Issues

• 100% Tie off – Fall Protection
• Accessibility – Handlance
• Close working distance
• PPE for handlance use.

Shotcrete Repair

Shotcrete was the recommend repair:

• Accessibility
• Quantity of material
• Durability

FHWA Required Testing

• Mix design submittal
• Material Certifications
• Compressive strength
• Test panels for core grading
• Shrinkage testing
• Bond testing performed on field mockup

Shotcrete Specifications

• Compressive Strength 6000 psi
• Low to moderate shrinkage
• Bond strength of

Material

Selected a pre-blended material:

• Type 1 Portland Cement
• Silica-fume
• Aggregate –ACI 506.2 –Gradation #2
• Design strength of 7,250 psi

Shrinkage

Shrinkage requirement: Low to Moderate

• Cast 3 -3”x3”x11-1/4” prisms
• Drying shrinkage measurements at 7, 14, 21 & 28 days
• Avg. results –0.047%, 0.064%, 0.075% and 0.076%
• ICRI TG 3733
  • –Low shrinkage = 0.025 –0.050%–
  • Moderate shrinkage = 0.050% -0.10%
• Meets requirement

Test Panel Preparation

Three test panels were prepared to perform various test:

• One unreinforced panel –wood form
• One reinforced panel containing #11 bars @ 10” OC and #4 stirrup bars @ 6” OC –wood form
• One reinforced concrete test panel made at the project site and shipped to the repair contractor’s site

Test Panel – 1

• Unreinforced panel
• Core grading –ACI 506.2 –Grade 2 or better –Excellent Results
• Compressive strength –average 8,180 psi

Test Panel – 2

• Reinforced panel
• Core grading –ACI 506.2 –Grade 2 or better –Excellent Results
• Core visually graded by FHWA officials.

Test Panel – 3

Reinforced concrete panel, water blasted with 20,000 psi to simulate hydrodemolition profile.

• Bond test –ICRI TG 3739
• Average direct tensile strength –259 psi @ 14 days
• Shotcrete Approved for Repairs

Shotcrete Repairs

• Approx. 60 cubic feet installed
• Ridley C-9 dry mix gun•375 cfm
• Shotcrete work accepted
• Construction continues
• Schedule completion of the arch bridge mid-2010
• Open to traffic by the end of 2010