06 historic stadiums freeze thaw
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www.sgh.com
Specialized Surface Preparation
and Repair of Historic Stadiums with
Freeze-Thaw Damage
Liying Jiang, P.E.
Timothy Montgomery, P.E.
18 April 2012
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Description of Structure
Cast-in-place concrete Stadia Raker beams
Seat slabs and riser beams
Usually have elastomeric coating on topside
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Typical Damage At Stadia
Corrosion
Failed joints
Condensation
Organic growth
Freeze-Thaw Deterioration
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Freeze-Thaw Deterioration
Occurs when water gets
into the concrete andfreezes. Ice formation is expansive,
so it creates tensilestresses in the concrete.
It is a progressive failure,
starting at the surface andworking its way into theconcrete.
Modern concretes use airentrainment, but those onlycame into widespread usein the 1950s, well aftermost cast-in-place stadiawere built.
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Freeze/Thaw Repair Is Complicated By
Damage is widespread, and often concealed
Variability in damage
Cracking that is interconnected
Fragility of concrete in direction parallel to exposed face
Exposed nature of the concrete in use Requirement to prevent trapping moisture
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Owner Concerns
How will the repaired stadium look?
Like new would essentially require complete demolition
Is the level of damage possible to repair?
Conventional techniques may be inadequate Special construction methods
Additional oversight of repair demolition and surface preparation Close collaboration between all parties
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Owner Concerns & Costs
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LeaveAlone
LikeNew
$
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Repair Approach: Coat and Pray
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Owner Concerns & Costs
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LeaveAlone
LikeNew
$
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Repair Approach: Blow and Go
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Owner Concerns & Costs
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LeaveAlone
LikeNew
$ Manage Owner Expectations
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Repair Approaches: TLC
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IMPLEMENTING THE REPAIRS
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Coating Removal
Concrete Repairs
Testing and Inspection of Concrete Repairs
Waterproofing Preparation & Installation
Implementing the Repairs
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Coating Removal
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Coating Removal
Hydrodemolition: the superior method of coating removal
Mower with rotating head for bulk removal Lance for removing remainder
High-pressure: 35,000 psi
Removes coating and unsound concrete near surface
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Video of Hydro Mower
Coating RemovalMower
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Coating RemovalMower
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Remove coating from vertical surfaces and edges of
treads/risers
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Coating RemovalLance
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Video of Hydro Lance
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Coating RemovalLance
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Coating RemovalIdentifying Deterioration
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Next goal is to determine extent & depth of repairs
Implement conventional condition inspection
Identify extents of deterioration: Chain drag on horizontal surfaces
Hammer sounding on vertical surfaces
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Concrete RepairsCondition Inspection
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Concrete RepairsCondition Inspection
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Next goal is to determine depth of repairs
Choice of demolition method: Hydrodemolition
No microcracking
Fully prepares concrete and reinforcing surfaces
Slower rate of removal; typically higher cost/sq ft Electric Chipping Hammers
Induces microcracking
Additional surface preparation usually required (sand blast)
Can result in lower bond strengths
Owner often prefers this method due to schedule
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Concrete RepairsPartial vs. Full Depth
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Electric Chipping Hammer Demolition:
Saw-cut the perimeter of repair BEFORE removing all loose andunsound concrete.
Minimize bruising and microcracking of good concrete byremoving concrete in thin lifts; inspect surface after each lift
Require Engineer approval of each repair
Growth of repair extents: vibrating reinforcing steel andadjacent sound concrete
Determination of partial-depth vs. full-depth is made on acase-by-case basis
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Concrete RepairsBest Practices
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Concrete RepairsPartial-Depth Nosing
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Concrete RepairsPartial-Depth Tread
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Concrete RepairsFull-Depth Demolition
Inspect full-depth repair
edges to determine ifadditional demolition isneeded
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Concrete RepairsRepair Mortar Placement
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Sounding repairs (hammer)
Direct-Tension Pull-Tests Measure average bond stress
Failure to be minimum 150 psi orwithin substrate
Require frequent tests initially inproject to verify demolitionmethod is providing adequatebond
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Testing Partial-Depth Repairs
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Waterproofing Preparation
Alternatives for waterproofing preparation:
Cementitious parge coat (continuous) Installing localized epoxy products at pits, grooves, or voids
Parge CoatEpoxy Mortar
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Waterproofing Preparation
Insert photo of pargecoat
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Waterproofing Installation
Choose a robust waterproofing system
Sand-filled urethane base coat Conduct mock-up to confirm amount of sand relative to surface
irregularity
Waterproofing Installation Sand Filled Urethane
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Waterproofing InstallationSand-Filled Urethane
Base Coat
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Waterproofing InstallationIntermediate Coat
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Waterproofing SystemFinished Appearance
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Summary
Stadium work can be very interesting and rewarding,
They present challenges to conventional thinking Can they be like new?, Can marginal concrete remain?, When
do we stop?
Successful projects require careful alignment of goals
and expectations of all parties, Careful and proper preparation is key,
Use selective hydrodemolition as a screening tool,
Close cooperation and inspection is required.
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Questions?
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