The construction challenges of high pier columns of urban viaducts are mainly reflected in three aspects, namely the connection of main reinforcement bars, the control of concrete quality, and the vibration of concrete.

1) Connection of main reinforcement bars

Due to the relatively high height of the pier columns, when embedding the main reinforcement bars of the pier columns in the cap, it is impossible to install them in place at one time. They need to be installed in sections. The connection form between sections generally adopts lap welding. A crane is required to cooperate with workers to fix the lapped reinforcement bars, and then the welding workers stand on the high scaffold platform to carry out vertical welding. Therefore, it is required that the welding workers not only have a high level of professional skills but also have strong ability to resist external environmental interference. In short, the construction difficulty is relatively high.

2) Control of concrete quality

The performance indicators of concrete mainly include workability, that is, fluidity (consistency), cohesiveness, and water retention. For the construction of concrete for high pier columns, a pump truck is generally used. Therefore, the fluidity of the concrete arriving at the construction site should meet the requirements of the mix proportion design. However, in the actual construction process, the fluidity of concrete will be affected by various factors such as raw materials, mixing time, transportation distance, and external temperature, and it may be larger or smaller. This situation often occurs especially when the transportation distance is long, the road traffic conditions are unclear, and the external temperature is high. Therefore, the mixing plant should make timely fine adjustments according to factors such as transportation time and temperature to ensure that the fluidity of the concrete arriving at the construction site meets the construction requirements. At the same time, the two indicators of cohesiveness and water retention are equally important. Otherwise, in the process of concrete construction, phenomena such as segregation and bleeding will occur. In mild cases, it will affect the appearance quality of the pier columns, such as the water streak phenomenon; in severe cases, it will affect the internal quality of the pier columns, such as unqualified concrete strength.

3) Vibration of concrete

Vibration is a key process in concrete construction, and the quality of vibration directly affects the compactness of the concrete. When constructing the concrete of high pier columns, the problem of how to vibrate the concrete often arises. For example, if the vibrator worker directly stands on the top of the pier column to vibrate, due to a height of up to 20 meters and the dim light inside the formwork, even if lighting lamps are installed and an extended vibrator rod is used, it is impossible to ensure that the vibration is sufficient and there is no situation of missed vibration. If the vibrator worker is directly sent to the bottom of the pier column to vibrate, because the stirrups inside the pier column are crisscrossed and the space is narrow, it is difficult for the vibrator workers to operate.

To Wrap Up

In conclusion, the construction of high pier columns of urban viaducts faces many challenges in aspects such as the connection of main reinforcement bars, the control of concrete quality, and the vibration of concrete. To ensure the construction quality and progress, construction units need to formulate scientific and reasonable construction plans, strengthen the management of construction processes, and improve the professional skills of construction personnel. Only in this way can the high-quality completion of urban viaduct projects be guaranteed.