Preventing concrete leakage in tunnel lining formwork is crucial for the structural integrity, durability, and aesthetics of the tunnel. Leakage can lead to honeycombing, voids, exposed rebar, and ultimately compromise the lining’s performance.
How to prevent concrete leakage in tunnel lining formwork
I. Formwork Design and Fabrication:
Tight Joints: This is paramount. Formwork panels must be precisely manufactured and assembled to ensure minimal gaps.
Sealing Materials: Use appropriate sealing strips, gaskets, or expandable foam at all joints between formwork panels and at interfaces with existing structures.
Overlapping: Where possible, design formwork panels with overlapping sections to create a tighter seal.
Rigidity and Strength: The formwork must be strong enough to withstand the pressure of fresh concrete without deformation or deflection, which can create gaps.
Adequate Bracing and Support: Ensure the formwork is properly supported and braced to prevent movement during concrete placement and vibration.
Through-Ties and Wall Bolts: Use sufficient and correctly installed through-ties or wall bolts to secure the formwork. Ensure these penetrations are sealed effectively after removal.
Cleanliness and Release Agent:
Clean Surfaces: Before concrete pouring, thoroughly clean the formwork surfaces to remove any debris, dust, or hardened concrete that could prevent a tight seal.
Release Agent Application: Apply a suitable release agent evenly to the formwork surface. This facilitates easy stripping and helps prevent concrete from sticking to the formwork, which can damage the concrete surface and lead to leakage paths during subsequent pours.
Precision in Dimensions: The formwork should be manufactured to precise dimensions to ensure a snug fit and minimize gaps.
II. Construction Practices During Concrete Pouring:
Concrete Mix Design:
Appropriate Slump: Use a concrete mix with the correct slump (workability) for tunnel lining. Too high a slump can lead to excessive bleeding and segregation, while too low a slump can make compaction difficult and increase the risk of voids.
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