Precast T beam is a crucial aspect of bridge construction, and if the quality of the T-beams is not up to par, it can lead to a decrease in overall construction efficiency. To further improve the level of bridge construction, this article introduces five aspects of quality control for Precast T-beams.

1.Raw Materials

Concrete is the most commonly used material in bridge construction projects and the quality of sand and stones in concrete directly affects the elasticity and arching of T girder. Therefore, strict control should be exercised over the selection and application of construction materials during the prefabrication of T beam mould.

The precast T-beams have a relatively high strength grade, while concrete has little impact on its strength due to its water-cement ratio. Therefore, cement varieties with relatively low shrinkage and hydration heat should be selected, and the stability of the cement should be strictly controlled. Up to 10% to 20% of fly ash or 20% to 30% of mineral powder can be incorporated into precast T-beams. The sand and stone materials should meet relevant technical specification requirements, especially the raw materials must meet the II-class technical requirements for fine and coarse aggregates, and the crushed stone should be of continuous grading with particle sizes ranging from 5 to 20 mm. As for admixtures, it is preferable to use 1st-grade polymer light acid high-efficiency water reducers with early strength, delayed setting, a small air-entraining amount, and low dosages, which should meet the relevant requirements of the "High-performance Water Reducing Agent of Polycarboxylic Light Acid Series." When construction is carried out in harsh weather conditions, the setting time of admixtures should be appropriately adjusted, and the setting time of the concrete should be extended to control the construction environment temperature and time.

2. Concrete Mix Proportion Design

Through experiments, optimize and control the concrete mix proportion to ensure the workability of concrete, while controlling the cement dosage and water usage. Increase the usage of crushed stone appropriately and improve the volume stability of concrete. When determining the mix proportion, multiple designs should be implemented for different sand content, water-cement ratio, and admixtures. The goal is to meet the requirements for concrete strength and elastic modulus, as well as improve the workability and appearance quality of concrete, while minimizing issues like bubbles and water marks.

3. T Beam Formwork

The steel mold for precast T-beams should be manufactured by specialized manufacturers. The surface flatness of the steel formwork and the bolt connection holes between different templates must meet corresponding precision requirements. For T beam templates with rust on the internal surface, comprehensive cleaning is required before assembly. High-quality demoulding agent should be used to ensure uniform coating and prevent damage to the appearance of concrete caused by the formwork.

In order to prevent leakage of grout, rubber strips need to be attached to the side of the pedestal and assembled symmetrically from the middle to both sides. After assembly, it is necessary to connect the tie rods of the pedestal in time and adjust the transverse slope of the wing plate. To ensure the overall stability of the formwork, the tie rods between the pedestal and the top of the beam need to be tightened. Soft rubber strips should be used to fill the panel connection position between the two templates. After clamping the panel, the rubber is squeezed and deformed to block the control joint between the panels, effectively controlling grout leakage.

When installing the formwork of corrugated pipe end anchor plates, end pieces, and gear plates, foam sealant should be used to optimize the joint position of the templates with an attached vibrator. The end mould should be equipped with an attached vibrator in time to prevent insufficient vibration of the concrete under the anchor plate. Vertical connections should be realized using grouting sleeves, and the height of horizontal joints should be designed to be about 20mm, and grouting should be used to fill them. The steel bars connected through the sleeves can use a standard center single row with a spacing of less than 400mm, and the steel bar area should be determined through calculation. The connected steel bars can use large diameters to reduce the number of steel bars as much as possible and improve the efficiency of industrialized construction.

4. Concrete Pouring

The construction of precast T girder requires the use of post-tensioning construction method. Three corrugated pipes are arranged internally, and it is inconvenient to use embedded vibrators to vibrate the concrete under the corrugated pipes. The connection between the horseshoe part and the web plate is mainly inclined, and during the vibration process, it is difficult to eliminate bubbles. At this time, the concrete in the anchor zone and the bottom of the end needs to be separated by corrugated pipes, with a high reinforcement ratio. During the pouring process, problems such as slurry enrichment, grout leakage, and insufficient vibration compaction are prone to occur. Therefore, strict control is required for the pouring construction of precast T-beams. The slump and cohesion of the mix should be strictly controlled. The concrete under the corrugated pipes should be treated with attached vibrators. For areas with difficult vibration and corners of the formwork, small-diameter embedded vibrators or insertion rods should be used for auxiliary vibration treatment.

5. Concrete Pouring

The construction of precast T girder requires the use of post-tensioning construction method. Three corrugated pipes are arranged internally, and it is inconvenient to use embedded vibrators to vibrate the concrete under the corrugated pipes. The connection between the horseshoe part and the web plate is mainly inclined, and during the vibration process, it is difficult to eliminate bubbles. At this time, the concrete in the anchor zone and the bottom of the end needs to be separated by corrugated pipes, with a high reinforcement ratio. During the pouring process, problems such as slurry enrichment, grout leakage, and insufficient vibration compaction are prone to occur. Therefore, strict control is required for the pouring construction of precast T-beams. The slump and cohesion of the mix should be strictly controlled. The concrete under the corrugated pipes should be treated with attached vibrators. For areas with difficult vibration and corners of the formwork, small-diameter embedded vibrators or insertion rods should be used for auxiliary vibration treatment.

To Wrap Up

Precast T beams are important components in bridge construction projects, and their quality has a direct impact on overall construction efficiency. In order to improve the level of bridge construction, It is important to choose concrete materials reasonably, optimize mix design, strictly control formwork quality, carry out concrete pouring in a proper manner, and properly perform formwork removal and curing. Only in this way can the quality of precast T-beams be ensured and overall construction efficiency be improved.