Bio-based surface treatments for concrete durability: exploring the corrosion-inhibiting properties of Costus afer and Chrysophyllum albidum leaf extracts on fungal growth

Abstract

Concrete structures are vulnerable to deterioration caused by microbial colonization and the corrosion of embedded steel reinforcements. Although conventional synthetic coatings and chemical inhibitors can be effective, they raise environmental and economic concerns. This study explores the use of ethanol extracts from Costus afer and Chrysophyllum albidum leaves as eco-friendly, dual-function additives for concrete protection. Phytochemical properties were analyzed using GC–MS and FTIR, while antifungal efficacy was assessed via the agar well diffusion method against fungal strains isolated from deteriorated concrete surfaces. Corrosion inhibition in simulated concrete pore solution [saturated Ca(OH)₂] was evaluated using potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and atomic force microscopy (AFM). In addition, geospatial techniques were applied to assess regional susceptibility to fungal biodeterioration. Landsat 8-derived normalized difference moisture index (NDMI) and land use/land cover (LULC) mapping assessments were conducted for Port Harcourt and Owerri to evaluate environmental drivers of microbial risk. Results showed that C. albidum exhibited superior antifungal activity across all isolates, with inhibition efficiencies of up to 99.8%. Surface analysis confirmed reduced roughness in treated samples. NDMI and LULC assessments revealed that vegetation moisture and impervious surface distribution strongly influence fungal colonization risk. This combined laboratory and remote sensing approach highlights the promise of C. afer and C. albidum extracts as sustainable, non-toxic additives for enhancing the durability of concrete structures, while emphasizing the need for region-specific environmental diagnostics in biodeterioration risk management.