# Carbonation and Corrosion Durability Assessment of Reinforced Concrete Beam in Heavy-Haul Railways by Multi-Physics Coupling-Based Analytical Method

## TL;DR

This paper studies how heavy train loads cause cracks in concrete beams, leading to faster corrosion and reduced durability, using a new multi-physics method.

## Contribution

A novel multi-physics coupling method is introduced to assess the durability of reinforced concrete beams under heavy-haul railway conditions.

## Key findings

- Heavy train loads cause up to 20% stiffness reduction in beams over 100 years, compared to 7.4% for lighter loads.
- Crack width, carbonation time, and corrosion rate are key parameters in the durability decline of concrete beams.
- Beam cracking significantly influences the rate of structural degradation under operational loads.

## Abstract

The operation of heavy-haul railway trains with large loads results in significant cracking issues in reinforced concrete beams. Atmospheric carbon dioxide, oxygen, and moisture from the atmosphere penetrate into the beam interior through these cracks, accelerating the carbonation of the concrete and the corrosion of the steel bars. The rust-induced expansion of steel bars further exacerbates the cracking of the beam. The interaction between environmental factors and beam cracks leads to a rapid decline in the durability of the beam. To address this issue, a multi-physics field coupling durability assessment method was proposed, considering concrete beam cracking, concrete carbonation, and steel bar corrosion. The interaction among these three factors is achieved through sequential coupling, using crack width, carbonation passivation time, and steel bar corrosion rate as interaction parameters. Using this method, the deterioration morphology and stiffness degradation laws of 8 m reinforced concrete beams under different load conditions, including those of heavy and light trains in heavy-haul railways, are compared and assessed. The analysis reveals that within a 100-year service cycle, the maximum relative stiffness reduction for beams on the heavy train line is 20.0%, whereas for the light train line, it is only 7.4%. The degree of structural stiffness degradation is closely related to operational load levels, and beam cracking plays a critical role in this difference.