Effect of Grouting Materials on the Cathodic Protection Effectiveness of Shield-Crossing Pipeline

Abstract

This study established a full-scale test platform to measure the polarization curves, instant-off potentials, and current distribution of carbon steel pipes under combined cathodic protection (CP) in three grouting materials (fly ash concrete, foam concrete, bentonite concrete), soil, and sand. CP simulations were conducted for validation, and the potential distribution under various working conditions was investigated. The results show that the open-circuit potential (OCP) of carbon steel pipes in soil is significantly more negative than that in concrete or sand, thereby elevating the risk of galvanic corrosion at transitions where the pipeline crosses different media. Polarization results indicate that the current density required to achieve the same degree of polarization for carbon steel follows the order: soil > foam concrete > bentonite concrete > fly ash concrete > sand. Under low CP current conditions, the galvanic effect dominates, causing protection current to converge toward regions with higher potential. At high CP currents, differences in cathodic polarization behavior become dominant, elevating and homogenizing the potential level into the effective protection range.