Hydration Heat Temperature Field of Large-Diameter Steel Tube Concrete Components in Complex Environments

Overview of the Study

This paper by Zhou Qian, Feng Pengcheng, Zhou Jiangting, Jing Shihong, Zheng Guohui, and Zhang Wenfeng, published in "Concrete" (2023, Issue 3, pp. 148-153), investigates the hydration heat temperature field of large-diameter steel tube concrete components under combined effects of strong solar radiation, large diurnal temperature variations, and cement hydration heat. Funded by the Chongqing Natural Science Foundation (Grant No. CSTB2022NSCQ-MSX0661) and the Chongqing Transportation Industry Science and Technology Program (Grant No. KJXM2021-0966), the study applies ANSYS transient thermal analysis to reveal the temperature field distribution characteristics and evolution mechanisms in large-span steel tube concrete arch bridges in plateau regions.

Core Technical Findings

The study reveals several important temperature field characteristics:

• The central concrete temperature initially increases due to hydration heat and then decreases to a stable temperature as hydration progresses.
• The outer concrete temperature near the steel-concrete interface exhibits sinusoidal time-varying behavior with amplitude increasing toward the interface.
• The sunny-side maximum temperature exceeds the shaded-side maximum temperature by approximately 20 degrees Celsius.
• At midday, the temperature distribution from the sunny side to the center follows a pattern of first decreasing then increasing, with the turning point located at D/8 from the interface (where D is the diameter).
• From the center to the shaded side, temperature gradually decreases.
• At night, concrete temperature distributes symmetrically along radial directions, with the segment from D/4 to the center showing higher and more uniform temperatures.
• The maximum temperature gradient on the sunny and shaded sides varies sinusoidally with time.
• The diurnal temperature difference in the radial segment from D/8 to the center approaches a constant value, approximately 1/8 of the diurnal temperature difference at the sunny-side interface.

Technical Parameters and Temperature Field Characteristics

The hydration heat temperature field is a transient phenomenon that occurs during the early age of concrete hardening. For large-diameter steel tube concrete components, the heat generated by cement hydration is significant and can cause substantial temperature differences between the core and the surface. These temperature differences induce thermal stresses that may crack the concrete or affect the bond between the steel tube and concrete.

Finite Element Modeling and Validation

The ANSYS transient thermal analysis model incorporates the following key features:

• The steel tube and concrete core are modeled as separate regions with appropriate thermal properties.
• The thermal contact between the steel tube and concrete is modeled with a contact conductance that accounts for the bond quality.
• The boundary conditions include solar radiation on the sunny side, convective heat transfer on all exposed surfaces, and the internal heat generation from cement hydration.
• The hydration heat generation rate is modeled as a function of time and temperature, following established models such as the Sahin model or the modified Arrhenius model.

The study validates the finite element results against experimental measurements, confirming that the numerical model achieves engineering-level accuracy. This validation is critical for the application of the model to practical design problems.

Engineering Practice Implications

For steel tube concrete bridge construction, the temperature field study has several important implications:

1. Thermal cracking risk: The temperature gradients induced by hydration heat and solar radiation can cause thermal stresses that exceed the tensile strength of early-age concrete. Engineers must implement temperature control measures during construction, such as internal cooling pipes, external insulation, and controlled pouring rates.
2. Steel tube deformation: The differential thermal expansion between the steel tube and concrete core can cause relative movement and interface slip. This is particularly critical for large-diameter tubes where the thermal gradient is more pronounced.
3. Long-term performance: The temperature field affects the long-term properties of the concrete, including strength development, shrinkage, and creep. The hydration heat temperature distribution influences the microstructure development of the concrete, which in turn affects its mechanical properties.
4. Weld quality: The temperature field near weld joints in the steel tube can affect the weld residual stress distribution and the risk of hydrogen-induced cracking. Engineers should consider the thermal history during construction when evaluating weld quality.

Key Questions and Reflections

The study raises important questions about the adequacy of current design codes for steel tube concrete structures in extreme environmental conditions. The combined effects of hydration heat, solar radiation, and large diurnal temperature variations create a complex thermal environment that may not be adequately addressed by simplified design approaches. Engineers should consider the full thermal history of the structure during design and construction to ensure long-term performance.

The finding that the sunny-side maximum temperature exceeds the shaded-side maximum temperature by approximately 20 degrees Celsius highlights the significant impact of solar radiation on the thermal environment. This temperature difference can induce substantial thermal stresses in the steel tube and concrete core, and engineers should incorporate these effects into their design calculations.

Study Insights and Recommendations

This research provides valuable insights into the temperature field behavior of large-diameter steel tube concrete components under complex environmental conditions. The findings have direct implications for the design, construction, and long-term performance assessment of steel tube concrete arch bridges in plateau and mountainous regions. For steel pipe fabrication and welding engineers, the study emphasizes the importance of considering thermal effects during construction, particularly the interaction between hydration heat and environmental temperature variations. The validated finite element model provides a powerful tool for predicting temperature fields and thermal stresses, enabling engineers to optimize construction procedures and implement effective temperature control measures. This research should inform future design standards and construction guidelines for steel tube concrete structures in extreme environments.