1.Mould Treatment and Release Agent Application
Mould Inspection and Cleaning:
First, conduct a comprehensive inspection of the steel mold for flatness and cleanliness. Use an angle grinder or wire brush to remove residual concrete slurry, rust, and welding slag from the mold surface, ensuring no foreign matter adheres to the inner walls of the mold.
2. Release Agent Application:
Select a high-quality professional mold release agent (e.g., hydraulic oil, emulsified oil, or water-based release agent). Apply it evenly and without omission to the inner walls of the mold cavity using spray equipment or a long-nap roller.
3. Prestressing Tendon Installation and Tensioning
Prestressing Wire (Strand) Arrangement:
According to the design drawings, precisely thread the pretreated prestressing wires or strands into the reserved ducts or positioning grooves. Adjust their positions to ensure that straightness and concrete cover thickness comply with specifications.
Tensioning:
Use intelligent tensioning equipment or hollow-core hydraulic jacks to apply tension. The tensioning process follows the "dual-control" principle (tension force as the primary control, with elongation value as a secondary verification).
Load Holding and Anchoring:
After reaching the designed tensioning control stress, maintain the load for 2 to 5 minutes to minimize elastic losses of the wires and deformation losses of the anchors, then proceed with anchoring.
4. Concrete Pouring and Compaction Process Concrete Placement:
Use a hopper or pumping method to place the mixed concrete into the mold in layers. Control the concrete slump to meet the specified requirements.
Combined Vibration Process:
To enhance concrete density and surface quality, a combined vibration process using internal vibrators and external vibrators is adopted.
5. Finishing and Troweling
Rough Leveling:
After vibration is completed, use a straightedge to strike off the concrete along the top surface of the formwork, removing excess laitance.
Final Troweling:
Before initial setting of the concrete (typically 2–4 hours after pouring, depending on temperature), use a rotary power trowel to perform a large-area finishing operation that brings the paste to the surface. Subsequently, manually finish the beam ends, corners, and areas around embedded components with a steel hand trowel to ensure that the flatness of the top surface is controlled within ±5 mm. Finally, brush or texture the surface to enhance bond strength with the bridge deck overlay.
6.Curing and Resting
Covering and Moisture Retention:
Immediately after finishing, cover the beam with geotextile fabric or plastic sheeting. Sprinkle water over the beam surface and the geotextile fabric to maintain a continuously moist condition.
Resting for Hardening:
Allow the beam to rest and cure under ambient temperatures not lower than 5°C. Ordinary concrete requires a resting period of 24 hours (the exact duration is determined by the strength of companion cube specimens cured under the same conditions) to achieve demolding strength, which is typically no less than 70%–80% of the specified design strength.
