# Unveiling the Degradation Mechanism of Impermeability and Pore Structure in Concrete Under Long-Term Water Exposure

## TL;DR

This study examines how long-term water exposure affects concrete's impermeability and pore structure in dam sections over 75 years old.

## Contribution

The paper reveals the degradation mechanism of concrete impermeability caused by crystallization pressure and carbonation in coastal environments.

## Key findings

- The downstream section of the main dam shows significantly lower water permeation resistance compared to other sections.
- Mercury intrusion porosimetry indicates higher pore diameters and porosity in the downstream section.
- Crystallization pressure and carbonation are identified as key factors in structural loosening and porosity increase.

## Abstract

To investigate the evolution of impermeability and pore structure in concrete under long-term service, systematic tests were conducted on submerged concrete from dam sections with over 75 years of service. Results show that the surface water permeation resistance index of concrete in the downstream section of the main dam is only 9.19 × 10−9, significantly lower than that of concrete from the upstream of the main dam (UMD), downstream of the main dam (DMD), upstream of the auxiliary dam (UAD), and upstream of the weir (UW). Moreover, its impermeability improves noticeably within the 0–100 mm depth range. Mercury intrusion porosimetry revealed that the median pore diameter, average pore diameter, pore content, and porosity in this region reach 306.7 nm, 55.4 nm, 35.64%, and 3.961 mm, respectively—all markedly higher than in other dam sections. Combined XRD and SEM/EDS analyses indicate that crystallization pressure from saline solutions in the coastal environment, together with long-term carbonation, leads to structural loosening and increased porosity in the downstream concrete of the main dam, ultimately degrading its impermeability performance.