The traditional construction process of precast T-girders has quality defects and control difficulties in formwork system, steel bar fabrication and installation, concrete construction and prestressed tensioning. Combined with the standard production requirements of precast girder yards and current bridge construction specifications, this paper carries out process optimization research from the four core working procedures above, and puts forward a construction optimization strategy suitable for precast T-girders production, so as to improve construction quality and guarantee the long-term service performance of bridge superstructure.

1. Optimization of Formwork System

(1) Formwork design optimization. Adopting modular design concept, the formwork is divided into base formwork, side formwork, end formwork and other modules connected by high-precision connectors with tight joints. Double sealing strips are arranged at joints to prevent grout leakage. The stiffness and strength of formwork are checked according to the force condition of girders, and the panel thickness and support specification are reasonably selected to avoid displacement and deformation during construction.

(2) Formwork fabrication and installation optimization. Numerical control cutting and welding are adopted to strictly control geometric dimension and surface flatness. Before installation, the formwork shall be cleaned, derusted and coated with release agent. Total station and other high-precision instruments are used for positioning and calibration to ensure accurate axis and elevation. Full framing support or section steel support is adopted, with strength and stability checking to bear construction loads.

(3) Formwork stripping optimization. The stripping time is determined by concrete strength test on reserved test cubes. Stripping follows the principle of “support later, strip first; support first, strip later” in sectional and layered way to prevent concentrated stress and cracks. Girder surface shall be protected from collision during stripping.

2. Optimization of Steel Bar Fabrication and Installation Technology

(1) Application of automatic steel bar processing technology. Automatic equipment including numerical control cutter, numerical control bender and steel mesh welding machine replaces manual work. It precisely controls cutting length and bending shape, stabilizes welding quality, improves processing accuracy and efficiency, and reduces labor intensity.

(2) Optimization of steel bar positioning. Special positioning fixtures are manufactured: positioning clamping grooves on base formwork fix longitudinal reinforcement for uniform spacing; high-strength concrete or plastic spacer blocks are mounted on inner side of side formwork to control cover thickness. Temporary supports together with binding and welding are used to fix steel skeleton and prevent displacement during concrete pouring.

3. Optimization of Concrete Construction Technology

(1) Mix proportion optimization. Based on design strength, durability and site environment, orthogonal test is used to optimize the dosage of cement, aggregate, admixture and additive. Proper fly ash and slag powder are mixed to reduce cement consumption, shrinkage and construction cost while improving workability and durability. High-efficiency water reducer is selected to lower water consumption and enhance concrete compaction and strength.

(2) Mixing and transportation optimization. Forced mixer is used with strict batching and proper mixing duration to guarantee uniform mixing. Raw material temperature is monitored and adjusted under extreme ambient temperature. Transit mixer truck keeps slow rotation to avoid segregation. Delivery routes and vehicle quantity are reasonably arranged to prevent initial setting before placement.

(3) Pouring and vibrating optimization. A full inspection on formwork, reinforcement and embedded parts shall be completed before pouring. Concrete is poured in layers with thickness no more than 30 cm, following the sequence “web first, flange later” in continuous placement. Inserted vibrator penetrates 5–10 cm into the lower layer. Vibration stops when mortar appears on surface, avoiding over-vibration or missing vibration. Dense reinforcement zones and chamfers are vibrated carefully to eliminate voids and bubbles.

(4) Curing optimization. Timely curing measures including water sprinkling, membrane covering and steam curing are adopted. Normal water curing lasts no less than 7 days, and 14 days for concrete with retarding admixture or impermeability requirement. Girder surface shall be kept wet to avoid drying shrinkage cracks. Sunshade is equipped under high temperature and strong wind; membrane or steam curing is applied in winter to keep temperature above 5 ℃ against freezing damage.

4. Optimization of Prestressed Tensioning Technology

(1) Selection and calibration of tensioning equipment. Jack, oil pump and pressure gauge are selected according to prestressing tendon type and design tension force, with rated capacity higher than design value for safety margin. Equipment shall be calibrated by qualified inspection institutes at intervals of 6 months or specified service cycles, and inspected before tensioning.

(2) Tension sequence and rate optimization. Symmetric tensioning is adopted to avoid additional internal force caused by uneven stress. Multi-strand tendons are tensioned in design sequence. Graded tensioning is implemented: initial stress is 10%–20% of design stress to eliminate relaxation; each incremental load accounts for 20%–30% of design stress with holding period for deformation observation. A 5–10 min holding stage is required before anchoring at design tension.

(3) Monitoring during tensioning. Automatic monitoring is applied for tension force, tendon elongation and girder deformation. Pressure sensors and displacement sensors collect real-time data. Strain and displacement measuring points are arranged on key sections. Tensioning shall be suspended immediately once deformation or stress exceeds allowable range for troubleshooting.

(4) Anchorage quality control. Qualified anchors and clamps are adopted. Anchors shall closely fit tendons with properly installed clips to prevent wire slipping or fracture. Anchorage retraction shall be measured and comply with specifications. Supplementary tensioning or anchor replacement shall be carried out if excessive retraction occurs.

Conclusion

This article covers the whole construction process of precast T-girders, including modular formwork installation, automatic steel bar fabrication, concrete proportioning, pouring & curing, as well as prestress monitoring and anchorage. Integrated with modular tooling, numerical control machining and automatic monitoring, the strategy effectively mitigates common defects such as grout leakage, steel bar offset, concrete cracking and inaccurate prestress. On-site parameters shall be adjusted dynamically according to raw material, yard condition and local climate. Supporting inspection and acceptance procedures help realize standardized and refined precast T-girder construction to meet requirements on structural safety, appearance and durability of modern bridges.