Plant Derived Natural Extracts and Nanoparticle Technologies for Corrosion Control in Reinforced Concrete: A Systematic Review of Mechanisms, Performance Metrics, and Emerging Hybrid Systems

Abstract

The corrosion of steel reinforcement remains the single most pervasive threat to the long‑term durability of reinforced concrete infrastructure worldwide, with direct economic losses estimated at trillions of dollars annually. Traditional corrosion protection strategies—epoxy coatings, cathodic protection, and synthetic chemical inhibitors—are often effective but face increasing scrutiny regarding their environmental footprint, long‑term reliability, and cost‑effectiveness in aggressive service environments. Over the past two decades, two alternative paradigms have emerged that align with the principles of sustainable construction: plant‑based “green” corrosion inhibitors and nanoparticle‑modified cementitious systems. This systematic review synthesizes findings from over 150 peer‑reviewed studies published between 2020 and 2026, with particular emphasis on the most recent advances in both fields. The first part of the paper examines the mechanistic basis of corrosion inhibition by botanical extracts, focusing on the adsorption behaviour of phytochemical constituents—flavonoids, tannins, alkaloids, and terpenoids—on steel surfaces under the high‑pH conditions characteristic of concrete pore solutions. Electrochemical data from more than 40 plant species are compiled and critically evaluated, with inhibition efficiencies exceeding 90% reported for several species in chloride‑laden simulated pore solutions at optimized concentrations. However, a recurring concern identified in the literature concerns heavy metal contamination of plant materials harvested from anthropogenically impacted environments; recent studies from Iran and elsewhere have documented measurable concentrations of lead, cadmium, and other toxic elements in medicinal plants, with significant implications for the safety of plant‑derived construction additives. The second part of the review systematically evaluates the role of nanoparticles—particularly nano‑silica, nano‑titania, carbon nanotubes, and green‑synthesised nanomaterials—in enhancing concrete durability through pore refinement, permeability reduction, and autonomous crack healing. Data from laboratory studies indicate that optimal nano‑silica addition (1.5–2.5% by cement weight) can reduce water absorption by up to 41%, decrease chloride permeability by 24–40%, and improve resistance against aggressive chemical attack by 39–42%. Bacterial–nano hybrid systems for self‑healing concrete have demonstrated healing efficiencies of up to 80% for cracks under 0.5 mm. The review concludes with a critical discussion of the knowledge gaps that remain, including the need for standardised testing protocols, long‑term field validation, and life‑cycle assessment of hybrid plant–nanoparticle systems.