Key Takeaways & Executive Findings
- •• Higher binder content slightly increases early-age thermal cracking risk in HSR bridge piers, but this can be offset by using low-heat cements and high-thermal-conductivity formwork. • A novel variable, “representative temperature rise for unit concrete,” integrates binder content, cement type, and formwork type to characterize the pier's inherent thermal property. • Three linear regression models were developed to predict the earliest safe demolding age, enabling engineers to optimize formwork removal timing without complex simulations. • The findings provide practical recommendations for mitigating early-age thermal cracking in high-altitude railway bridge construction, enhancing structural durability and safety.
Abstract
High-speed railway (HSR) bridge piers in high-altitude areas frequently face the challenge of early-age thermal cracking. This study employed numerical simulation methods to analyze the early-age temperature field, deformation field, and cracking risk of HSR bridge piers, considering three factors: binder content, cement types, and formwork types. The results show that the cracking risk slightly increases with a higher content of cementitious materials. However, this risk can be mitigated by selecting cements with lower heat of hydration and formwork materials with higher thermal conductivity. A variable termed “representative temperature rise for unit concrete” was proposed to integrate these three factors and comprehensively reflect the inherent thermal property of the pier. Subsequently, three linear regression models for predicting the demolding age of HSR bridge piers were established. These models empower engineers to determine the earliest feasible time for formwork removal without the need for complex computational analyses.
1. Introduction
By the end of 2023, the total mileage of China's high-speed railways has reached 45000 km, with transportation infrastructure such as railways and bridges continuing to extend into high-altitude regions such as the Qinghai-Tibet Plateau [1]. High-speed railway (HSR) bridge piers play a crucial role in the overall structure of the bridge. Compared to damage in the superstructure, pier damage may have a more significant impact on the bridge's performance [2]. The causes of pier damage can generally be attributed to several factors: dynamic loads (e.g., vehicle impact, wind loads, and earthquake action) [3, 4], environmental effects (e.g., solar radiation, atmospheric temperature fluctuations, and freeze-thaw cycles), and early-age cracking [5]. Early-age cracking accelerates concrete damage and failure under dynamic loads and environmental effects, leading to a decline in the long-term safety and durability of the structure [6]. However, for HSR bridge piers on plateaus, it remains uncertain how early-age deformation develops and how to mitigate the risk of early-age cracking.
The early-age deformation of concrete mainly consists of three components: early-age creep, shrinkage due to water loss, and thermal deformation caused by the heat of hydration and ambient temperature changes [7, 8]. For bridge pier components with adequate moist curing, the variation in concrete moisture is minimal, and thermal cracking is the primary factor contributing to early-age structural damage [9−11]. As depicted in Figure 1, prior to formwork removal, the release of hydration heat and the constraints from the formwork result in certain compressive stresses within the concrete, accompanied by stress relaxation over time. Following formwork removal, the surface temperature rapidly cools to ambient levels, while the internal temperature decreases more gradually due to the large volume and low thermal conductivity of concrete. This results in a significant temperature difference between the interior and the surface, leading to non-uniform thermal deformation within the structure. Consequently, the external surface develops tensile strains. When these strains surpass a critical threshold, cracking occurs. Therefore, identifying the time corresponding to the critical strain enables the determination of the earliest feasible formwork removal age, promoting timely removal. Upon further formwork removal delay, shrinkage cracking within the formwork may occur due to environmental cooling [7, 12, 13]. For bridge structures, several investigations have focused on the influence of temperature fields on the structure under solar radiation during later-age period, employing experimental research methods [14−17], theoretical analysis methods [18, 19], finite element analysis methods [20, 21], and a combination of the above methods [22−24]. However, research on the early-age temperature field
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YANG Jia-lin, YUAN Qiang, ZHANG Kai, GARBA Jamaa Mustapha, LI Qiu-yi, CHEN Lei, YU Cheng-long, LONG Xu-you (2025). Early-age thermal cracking behavior of high-speed railway bridge piers in plateau regions: Formwork removal recommendations. Journal of Central South University. https://doi.org/10.1007/s11771-025-6069-1
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Frequently Asked Questions
What is the main challenge addressed in this study?
The study addresses early-age thermal cracking in high-speed railway bridge piers located in high-altitude plateau regions, which is a significant durability concern.
What factors were considered in the numerical simulations?
The simulations considered three factors: binder content, cement types, and formwork types, to analyze their influence on temperature field, deformation, and cracking risk.
How can the cracking risk be mitigated according to the findings?
The risk can be mitigated by using cements with lower heat of hydration and formwork materials with higher thermal conductivity, which help reduce temperature gradients.
What is the 'representative temperature rise for unit concrete'?
It is a proposed variable that integrates the effects of binder content, cement type, and formwork type to comprehensively reflect the inherent thermal property of the pier.
What practical tools were developed for engineers?
Three linear regression models were developed to predict the earliest feasible demolding age, allowing engineers to determine formwork removal timing without complex computational analyses.
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