Durability of Post-Tensioned Structures Grout Specifications Durability Design Details

Durability and Post-Tensioning Extremely durable when properly constructed Crack control Multiple protection levels moisture, Cl-, CO2 concrete duct grout The grout is the last level of protection for the strand strand

Purpose of Grout Corrosion protection Bond

Properties Fluidity Bleed Segregation Set Time Strength Permeability Volume Change Corrosion Protection Bleed

Bleed in Grouts Bleed water is trapped in duct Higher vertical rises = higher pressures and more bleed water Strand promotes bleed by wicking Intermediate lense Bleed lenses form as a result of the separation of water from the cement. Ducts with vertical rises will typically experience more bleed due to the increased pressure within the grout column. Intermediate bleed water lenses may form in tall vertical ducts, leaving a void through the cross-section of the duct exposing the tendon. This sedimentation process is accentuated by the addition of seven-wire strand. The spaces within the individual twisted wires that form the strand are large enough to allow easy passage of water but not cement.

Bleed Lenses Voids Loss of protective environment 9 ¾” bleed column Intermediate lense

Keys to a Good Grout Completely fills duct Low permeability Appropriate bleed resistance Careful use of admixtures Detailed description of bleed lense formation and result. Exposed strand at high points in low vertical rise ducts. Possible completely exposed strand in areas for large piers. Many admixtures help one grout property while degrading another

Tasks under WO-81 Literature review and summary of current practice Development of specification language, details, and revisions to PennDOT publications Scope includes Grouting (materials, procedures, venting) Durability details (anchorage, duct material) Inspection/repair Training of personnel