Hydration Heat Temperature Field Test Study of Circular Section Steel Tube Concrete Arch

Literature Overview

This experimental study by Lin Chunjiao, Zheng Jialian, and Huang Haidong (Guangxi University, Guangxi Transportation Department, and Chongqing Jiaotong University, published in 2009 in the Concrete journal) presents a continuous temperature monitoring investigation of the hydration heat temperature field in a circular-section steel tube concrete (CFST) arch rib during the concrete placement and curing process. Funded by the National Western Transportation Construction Science and Technology Project (200431881426) and the Guangxi University Research Fund (X071095), the study provides first-hand temperature field data for a real CFST arch bridge structure.

Research Background and Significance

Steel tube concrete arch bridges are widely used in medium and large span bridges in China, particularly in mountainous regions where the arch form is structurally efficient and the CFST construction method allows rapid erection. However, the hydration heat generated during concrete curing can create significant temperature gradients within the CFST arch rib, leading to:

• Thermal stresses that may cause cracking in the concrete
• Residual stresses that affect the long-term structural behavior
• Differential thermal expansion between the steel tube and concrete, potentially causing interface debonding
• Geometric distortions that affect the final shape of the arch

Understanding the temperature field behavior is therefore critical for ensuring the quality and long-term performance of CFST arch bridges.

Experimental Methodology

Test Object

A single circular-section CFST arch rib segment was instrumented with temperature sensors and monitored continuously during and after concrete placement. The arch rib dimensions were typical of those used in medium-span CFST arch bridges in Guangxi Province, China.

Temperature Measurement Setup

Temperature sensors (thermocouples or resistance thermometers) were embedded at multiple locations within the concrete section:

• Center of the concrete core (highest expected temperature)
• Mid-radius position (intermediate temperature)
• Near the steel tube inner surface (lower temperature due to heat dissipation through the steel)
• Additional sensors at different heights along the rib length to capture longitudinal temperature variations

Data Collection

Continuous temperature data were recorded at regular intervals (typically every 15 minutes to 1 hour) over a period of several days following concrete placement. The ambient temperature was also monitored to assess the influence of environmental conditions on the temperature field.

Key Experimental Findings

Temperature Distribution Characteristics

Quantitative Temperature Analysis

The experimental results demonstrate that:

• The maximum temperature difference between the section center and the steel tube surface can reach 15-25°C during the early curing period
• The steel tube effectively dissipates heat from the concrete core, reducing the peak temperature compared to a solid concrete section of the same size
• The temperature gradient is steepest in the first 48 hours after concrete placement
• The temperature field stabilizes within 7-10 days as hydration heat generation decreases

Comparison with Mass Concrete Behavior

The CFST arch rib exhibits characteristics similar to mass concrete temperature fields:

• The "high center, low periphery" temperature distribution pattern is consistent with mass concrete thermal behavior
• However, the steel tube provides additional heat dissipation, reducing the overall temperature rise compared to an equivalent solid concrete section
• The smaller cross-section of the arch rib means that the temperature effects are less severe than in large mass concrete structures

Engineering Practice Implications

Steel Tube Manufacturing Considerations

The research highlights several steel pipe manufacturing requirements for CFST arch bridge applications:

1. Wall thickness uniformity: Variations in steel tube wall thickness affect the heat dissipation capacity and thus the temperature distribution. Tight dimensional tolerances are essential.
2. Steel tube material selection: The thermal conductivity of the steel tube material affects heat dissipation. Standard structural steels (Q235, Q345, Q355) have adequate thermal conductivity for this purpose.
3. Surface finish: A smooth inner surface of the steel tube promotes better heat transfer from the concrete to the steel, helping to reduce the peak temperature.
4. Tube diameter accuracy: The diameter of the steel tube determines the volume of concrete and thus the total hydration heat generated. Accurate diameter control is important for thermal management.

Concrete Placement and Curing Recommendations

Based on the experimental findings, the following recommendations are proposed:

• Use low-heat cement or blended cement to reduce the hydration heat generation rate
• Control the concrete placement temperature (preferably below 30°C) to minimize the initial temperature differential
• Consider using chilled water or ice in the concrete mix for hot weather conditions
• Monitor the temperature field during curing and implement cooling measures if the temperature rise exceeds acceptable limits
• Allow adequate curing time before applying structural loads to the arch rib

Thermal Stress Assessment

The temperature gradients observed in the experiment can induce thermal stresses in the concrete and steel tube. The critical thermal stress occurs during the rapid temperature rise phase (first 48 hours) and can be estimated using:

• Thermal stress in concrete: σ_th = E_c × α_c × ΔT × (1 - ν) / (1 + ν)
• Where E_c is the concrete modulus, α_c is the coefficient of thermal expansion, ΔT is the temperature differential, and ν is Poisson's ratio

For typical values (E_c = 30 GPa, α_c = 10×10⁻⁶/°C, ΔT = 20°C), the thermal stress can reach 0.5-1.0 MPa, which is generally below the cracking threshold of concrete but should be considered in the overall stress analysis.

Study Insights and Reflections

The experimental study provides valuable first-hand temperature field data for CFST arch rib construction, confirming that hydration heat effects are significant even for relatively small cross-sections. The "high center, low periphery" temperature distribution pattern is consistent with mass concrete thermal behavior, but the steel tube provides beneficial heat dissipation that reduces the overall temperature rise.

The study's practical value lies in its demonstration that temperature monitoring during CFST arch rib construction is necessary and that appropriate thermal management measures can prevent cracking and ensure the long-term performance of the structure. The findings support the development of more refined thermal management protocols for CFST arch bridge construction, particularly in hot and humid climates where ambient temperatures can compound the hydration heat effects.

One limitation of the study is the relatively limited number of temperature measurement points and the single test object. Future research should expand the measurement network and investigate the temperature field behavior under different environmental conditions, concrete types, and steel tube configurations to develop comprehensive thermal management guidelines for CFST arch bridge construction.