Long-term Deformation of Scale-Beam Concrete in Complex Plateau Environment

The plateau region is characterized by low air pressure, diurnal temperature, high annual irradiation, strong dry winds, and other complex environmental factors. These conditions have severe challenges to the shrinkage and creep of railway bridge girders, as well as to the control of their alignment. According to the engineering practice, the creep camber of precast prestressed simply supported girders in the plateau region increases significantly, adversely affecting track smoothness and train safety. It is thus crucial for providing a technical support for the design and construction of railway concrete simply supported box girders to clarify the long-term deformation behavior of beam concrete in this complex environment.

Two mix ratios and two curing methods were employed to create three sets of comparative working conditions. The JZ-NC was used for constructing simply supported box girders in Langcangjiang Special Bridge, China, with standard curing (NC). The JZ-SC shared the same composition but utilized steam curing(SC). The LSLC-SC incorporated a densifying modifier, primarily silica fume and calcium sulfate whiskers (3% by mass), along with a shrinkage-reducing agent (0.5% by mass), and also used steam curing. For each group, four scale-beam concrete specimens were prepared, i.e., two for creep testing and two for shrinkage testing. The scale-beam underwent a four-point bending loading mode, with upper and lower spans of 500 mm and 1500 mm, respectively, at a creep load of 2 kN. Strain gauges were installed in the compression and tension zones to monitor strain, while the LVDT displacement sensors measured beam deflection. The specimens were subjected to shrinkage and creep tests in a high-altitude exposure environment at 14 d.

A constitutive model for the long-term deformation of scale-beam concrete under the combined action of wet, heat and force fields was proposed using a software named ABAQUS and the secondary development function, and the long-term deformation of the model beam concrete was simulated.

Compared with standard curing, the scale-beam concrete subjected to steam curing shows a reduction of 6.2%, 7.1%, and 6.0% in shrinkage strain, compression zone creep strain, and tension zone creep strain for 365 d, respectively. Under the same curing conditions, the incorporation of dense modified materials and SRA effectively reduces the shrinkage strain of the concrete. The 365-d shrinkage strain, compression zone creep strain, and tension zone creep strain are decreased by 13.2%, 11.4%, and 19.1%, respectively, and the mid-span deflection of the scale-beam is decreased by13.8%, further verifying the regulatory effects of dense modified materials and shrinkage reducing agent.

The simulation results of the shrinkage and creep of the scale-beam concrete are in a reasonable agreement with the experimental results. The maximum error of the shrinkage strain is no more than 3%, and the maximum error of the creep is no more than 1%. This indicates that the established simulation method can well reproduce the long-term deformation behavior of the scale-beam concrete under the complex plateau environment.

The change in environmental temperature does not cause a uneven deformation in the scale-beam concrete, nor does it result in the warping of the scale-beam body, indicating that the temperature field mainly affects the longitudinal stress distribution of the scale-beam. The change in environmental temperature intensifies the redistribution of stress in the longitudinal section, and increases the shrinkage and creep of the concrete. Based on the micro-strain distribution characteristics caused by relative humidity, the humidity change does not lead to the warping of the scale-beam, indicating that the humidity field only affects the longitudinal stress distribution of the scale-beam, while the deformation coordination causes the stress to be redistributed between different sections, affecting the water migration and stress balance within the concrete, and exacerbating the shrinkage and creep of the scale-beam concrete.

Steam-cured concrete was prepared via incorporating a dense modified material (i.e., mainly composed of silica fume and calcium sulfate whiskers, with a mass fraction of 3%) and a shrinkage reducer (with a mass fraction of 0.5%) could effectively inhibit the shrinkage, creep and deflection deformation of scale-beam concrete in the complex plateau environment, and its 1-year shrinkage, compression creep and deflection reduction rates could reach 13.2%, 11.4% and 13.8%, respectively.

ABAQUS subroutine was written, and a numerical calculation framework for the long-term deformation of scale-beam concrete considering the temperature-humidity effects of the complex plateau environment was established, and the error between the simulation data and the measured results was less than 3%.

The temperature and humidity changes could mainly affect the longitudinal stress distribution of the scale-beam concrete, and the temperature-humidity effects in the complex plateau environment could intensify the stress redistribution on the longitudinal section, thus increasing shrinkage and creep.

The long-term deformation simulation of the scale-beam concrete at 50 a further verified that using the steam curing process, incorporating the dense modified material mainly composed of silica fume and calcium sulfate whiskers, and the shrinkage reducer could inhibit the shrinkage and creep of the scale-beam concrete in the complex plateau environment with the reduction amplitude of >17%.