In our previous article, we introduced the full construction workflow of precast box girders for bridges, covering beam yard preparation, reinforcement and corrugated pipe installation, formwork erection, concrete pouring, prestressed tensioning, duct grouting, end sealing, lifting and beam storage. Stable construction performance relies on systematic quality control. As a core superstructure component of bridges, the precision of box girder steel formwork and prestressed construction quality directly affect the forming effect and long-term durability of girders. Combined with field construction practice, this article sorts out key quality control points for precast box girder construction. It breaks down control standards for raw materials, concrete mix proportion, formwork tooling, prestressed tensioning and grouting, as well as inspection and acceptance of finished girders, helping projects stably produce qualified precast girders with complete sets of equipment such as bridge steel formwork and segmental box girder formwork.

Box gider formwork

(1) Raw Material Control Cement, sand and aggregate complying with national standards shall be selected to control material quality from the source. Cement shall meet GB175, while sand and aggregate shall satisfy design requirements on particle gradation, silt content and cleanliness. The material, specification, yield strength and tensile strength of reinforcement and steel strands shall conform to design documents. Batch inspection shall be carried out upon arrival to avoid defective materials with rust, cracks or bending damage. Concrete admixtures shall comply with relevant specifications. Admixtures for improving impermeability, workability and durability must pass compatibility tests with cementitious materials. Raw materials lay the foundation for the internal quality of girders formed by box girder steel formwork. Unqualified main materials will bring hidden structural risks for subsequent procedures.

(2) Concrete Mix Proportion and Mixing The concrete mix proportion shall be scientifically designed according to the service environment and load requirements of precast box girders to meet design indicators for strength, workability, impermeability, frost resistance and other durability performances. The feeding sequence, mixing duration and rotating speed shall be strictly controlled to ensure uniform mixing of cementitious materials, aggregate and admixtures and prevent uneven consistency or segregation. Slump shall be adjusted dynamically based on pouring procedures and formwork types. Too low slump hinders concrete flow and compaction inside box girder steel formwork, while excessive slump easily causes aggregate settlement and mortar-aggregate separation, leading to honeycombing and delamination.

(3) Formwork and Precasting Technology Precast box girder formwork (box girder steel formwork) shall have sufficient rigidity, flatness and dimensional accuracy to guarantee the girder alignment and section dimensions. Formwork cleaning and release agent application are critical steps to prevent concrete adhesion and obtain good surface finish after stripping. Concrete pouring adopts layered placement and layered vibration. For densely reinforced webs, high-frequency vibrators and immersion vibrators work together to compact concrete and discharge air bubbles. Vibration duration shall be properly controlled to avoid aggregate separation from over-vibration or honeycombing caused by insufficient vibration. Boyoun Heavy Industry provides customized inner, outer and end formwork for precast box girders, together with supporting T-beam formwork and pier column formwork. High-precision formwork helps reduce dimensional deviation during precasting.

(4) Tensioning and Grouting Technology Prestressed tensioning is the core quality control procedure for precast box girders. It shall be implemented strictly in accordance with the designed tension stress and sequence. Before tensioning, inspect intelligent tensioning equipment, steel strands and clip anchors; calibrate equipment regularly to ensure uniform tension and qualified strand stress. The tensioning rate shall be stable to avoid local stress concentration and girder cracking. After tensioning, double-control data including elongation and gauge reading shall be checked to confirm effective prestress transfer. For grouting, intelligent grouting machines are used. The mix proportion and fluidity of grout shall follow design requirements to ensure filling capacity. Grouting pressure and flow rate shall stay stable with smooth duct ventilation to fully fill prestressed ducts. Curing after grouting is required to develop grout strength and durability, which is vital to the long-term safety of the prestressed system.

(5) Inspection and Acceptance Systematic acceptance shall be performed for each precast box girder after stripping and grout curing. First, recheck overall dimensions including length, width, height, thickness of top and bottom slabs. Inspect surface defects such as cracks, honeycombs, voids and blowholes, and the girder surface shall be smooth. Concrete strength is tested by ultrasonic testing or core drilling. Prestress inspection includes stress testing of steel strands to verify whether the stress reaches the design value, and grouting compactness testing to confirm full duct filling.

Quality control of precast box girder construction runs through the whole process, covering raw material inspection, concrete mixing, box girder steel formwork management, prestressed tensioning and grouting, and finished girder acceptance. Every procedure must follow specifications and design requirements. Full-process quality control ensures the strength, stability and durability of precast girders and secures the safety of bridge superstructures. Shandong Boyoun Heavy Industry focuses on bridge formwork equipment. Besides box girder steel formwork and segmental box girder formwork, we also supply rhombus form travelers, tunnel lining trolleys and other complete bridge construction equipment with technical support to help beam yards achieve standardized, high-quality precast girder production.