Mechanical Performance and Microstructure Evolution in 56-Year-Old Aqueduct Concrete

The performance evaluation of aqueducts is crucial for the development of water conservancy and the protection of cultural relics. However, there are few effective methods for accurate evaluations of the mechanical performance of aqueducts. To investigate the changes in the concrete microstructure during the service life of aqueducts, this study conducted compressive tests on various parts of an aqueduct that has been in service for 56 years in Hunan Province, China. Additionally, scanning electron microscopy (SEM) scans and mercury intrusion porosimetry (MIP) tests were carried out on concrete samples taken from the side and bottom of the aqueduct tank. The compressive strength of the aqueduct concrete was 28.3–44.1 MPa, and the porosity of concrete was 10.98–17.57%. The pore structure of concrete is deteriorated by carbonation and water flow, which has a negative impact on the impermeability of the aqueduct. For concrete at the bottom of the tank, the internal pore structure was denser than the external one (with lower porosity and smaller average pore diameter). In contrast, the pore structure in other parts was the opposite. This difference was caused by the presence of flowing water. The types of internal pores in the concrete are basically gel pores and capillary pores. Finally, evaluation models considering the relationships between carbonation, compressive strength, porosity and permeation parameters of aqueduct concrete were proposed. The models can provide theoretical support for the performance evaluation and maintenance of aged aqueducts.