Construction methods · Precast concrete decks

Epoxy and dry joints, shear keys and temporary PT

The joint between match-cast segments: a thin epoxy layer squeezed by temporary bars until the permanent tendons take over, with multiple shear keys carrying the shear. Dry joints without epoxy were once used with external tendons but are now avoided in most codes for durability.

How bridges get built · Precast concrete decks · Epoxy and dry joints, shear keys and temporary PT

Also called: epoxy joint, dry joint, match-cast joint, temporary post-tensioning

How it is done

  1. Clean and roughen the match-cast faces; apply epoxy at the specified temperature and pot life to both faces.
  2. Bring the segment to the previous one, apply temporary post-tensioning bars to 0.3 MPa average, squeeze out the excess.
  3. Stress the permanent tendons within the epoxy's open time; inspect for squeeze-out around the full perimeter.

Where it fits

  • All precast segmental decks.

Where it does not

  • Epoxy in rain or outside temperature limits; dry joints in aggressive environments or with internal tendons.

Plant, pace and money

PlantEpoxy kits, temporary bars and jacks.
ProductivityAn hour per joint.
CostSmall per joint; the durability of the bridge rests on it.

Risks and controls

What goes wrong

  • Poor squeeze-out leaving voids, epoxy exceeding open time, water in the joint.

Quality assurance

Epoxy batch tests, temperature logs, squeeze-out inspection, temporary bar force.

Examples

AASHTO now requires epoxy joints for segmental bridges with internal tendons.

Related methods

Segment casting: short-line and long-line match castingSpan-by-span precast segmental with gantryPost-tensioning: tendons, stressing and grouting

Further reading

AASHTO Guide Specifications for Segmental Bridges · ASBI Handbook

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