Hydration Heat Temperature Field Analysis of Giant Steel Tube High-Strength Concrete Columns

Literature Overview

This 2023 publication in the Journal of Shenyang Jianzhu University (Natural Science Edition) by Wang Qiang and colleagues from Shenyang Jianzhu University investigates the hydration heat temperature field within giant steel tube columns filled with C70 high-strength concrete. Supported by the National Natural Science Foundation (52027811) and Liaoning Provincial Department of Education (lnsw202005), the research combines experimental temperature monitoring with finite element numerical simulation using MIDAS FEA software. The study examines the thermal behavior of these massive composite columns during concrete curing, with particular attention to the influence of internal steel components on the temperature field distribution.

Temperature Field Characteristics and Code Compliance

The experimental results reveal that the temperature control indicators for the C70 high-strength concrete specimens did not meet the requirements specified in GB 50496-2018 (Standard for Construction of Mass Concrete), yet the concrete placement quality still satisfied construction quality requirements. This discrepancy between thermal monitoring indicators and actual structural quality is an important finding that challenges the conventional approach of using temperature limits as absolute pass/fail criteria for mass concrete construction.

The study demonstrates that when internal steel components are included in the finite element model, the calculated temperature field correlates well with experimental measurements. However, when theoretical formulas are used to determine concrete thermal parameters for the simulation, the results deviate significantly from experimental data. This finding underscores the importance of using measured rather than theoretical thermal properties in temperature field predictions for these composite structures.

Thermal Behavior of High-Strength Concrete in Steel Tube Confinement

C70 high-strength concrete exhibits substantially higher heat of hydration compared to conventional concrete grades due to the higher cement content and the use of supplementary cementitious materials such as silica fume and ground granulated blast furnace slag. The steel tube confinement creates a unique thermal boundary condition that differs from conventional mass concrete structures in several important ways:

• The steel tube acts as a heat sink due to its high thermal conductivity (approximately 50 W/m·K for structural steel), absorbing heat from the inner concrete core
• The steel tube simultaneously provides thermal insulation from the external environment due to the low thermal conductivity of the air gap between the tube wall and the surrounding medium
• The thermal expansion mismatch between steel (12 × 10⁻⁶ /°C) and concrete (10-14 × 10⁻⁶ /°C) generates thermal stresses at the interface during temperature gradients
• The confined geometry restricts thermal cracking propagation compared to unconfined mass concrete

The internal steel components—typically including longitudinal reinforcement cages, transverse ties, and embedded connection plates—create localized thermal gradients within the concrete mass. These internal steel elements have higher thermal conductivity than the surrounding concrete and therefore create preferential heat dissipation paths that result in non-uniform temperature distribution.

Construction Quality Control Implications

From my extensive experience in steel pipe and structural steel welding, the temperature field analysis presented in this study has direct implications for construction quality control practices. The welding of internal steel components within the steel tube column creates residual stresses that interact with thermal stresses during the hydration curing period. The combined stress state may exceed the yield strength of the weld metal or the HAZ, potentially causing:

• Residual stress relaxation through plastic deformation in the HAZ
• Distortion of the internal steel cage geometry
• Micro-cracking in the weld metal or base metal at locations of high thermal gradient
• Differential cooling rates between thick and thin section welds creating complex residual stress patterns

The recommendation to reduce the hydration reaction rate to improve the temperature field is practically achievable through several methods:

• Incorporating retarder admixtures into the concrete mix design
• Using lower cement content with higher proportions of supplementary cementitious materials
• Implementing staged concrete placement with controlled intervals between lifts
• Employing internal cooling pipes within the concrete mass
• Applying external insulation blankets to reduce surface cooling rates

Study Insights and Engineering Recommendations

The conclusion that C70 high-strength concrete temperature control indicators may be appropriately relaxed represents a significant departure from conventional mass concrete construction philosophy. This finding is supported by the evidence that concrete placement quality remains acceptable even when thermal monitoring indicators exceed code limits, suggesting that the steel tube confinement provides sufficient restraint to prevent thermally induced cracking.

However, I emphasize that this relaxation should not be interpreted as permission to ignore temperature monitoring entirely. The temperature field within these giant steel tube columns is complex and non-uniform, particularly when internal steel components are present. The finite element analysis demonstrates that accurate prediction requires inclusion of these internal components in the computational model, and that theoretical thermal parameters may yield results that deviate substantially from reality.

For engineering practice, I recommend that projects involving giant steel tube high-strength concrete columns implement comprehensive temperature monitoring programs that include embedded thermocouples at multiple depths and locations, surface temperature measurement, and continuous data logging. The monitoring data should be compared against both code requirements and the more nuanced criteria suggested by this research to make informed decisions about construction quality. Welding procedures for internal steel components should be optimized to minimize residual stresses, and post-weld heat treatment should be considered for critical connections to ensure that the combined thermal and residual stress state does not compromise structural integrity during the hydration curing period.