Sustainable Backfill Design Strategies for Mitigating External Corrosion in Buried Ductile Iron Pipelines

The long-term integrity of buried ductile iron pipelines is increasingly compromised by external corrosion, especially where protective coatings are damaged or direct soil contact occurs. While coatings and cathodic protection remain essential for corrosion control, their long-term performance is strongly governed by the surrounding soil environment. In highly corrosive or moisture-retentive backfills, these conventional systems can degrade rapidly, leading to reduced protection efficiency and frequent maintenance. However, backfill design in current practice is primarily driven by mechanical considerations, such as providing adequate stiffness rather than corrosion resistance. To maximise the effectiveness of both structural support and corrosion protection, backfill properties should be understood from an integrated geotechnical and materials perspective; a connection that remains poorly understood. This review synthesises existing knowledge in both fields to demonstrate how key soil parameters such as moisture content, resistivity, pH, ion concentration, gradation, and compaction collectively influence the corrosion kinetics. Complementing the literature review, industry survey data from Australia provide insight into practical challenges and maintenance strategies. Findings highlight the need for performance-based backfill design to extend pipeline service life, reduce maintenance frequency, and support carbon-reduction goals in civil infrastructure.