An Evidence-Based Framework for the Sustainable Rehabilitation of Corrosion-Damaged Historic Marine Structures

Abstract

This paper presents a validated, data-driven framework for the sustainable rehabilitation of corrosion-damaged marine infrastructure, demonstrated through a comprehensive study on a historic coastal structure. The implemented three-phase methodology—integrating advanced condition assessment, evidence-based intervention design, and rigorous performance validation—successfully addressed severe chloride-induced deterioration. Diagnostic quantification revealed that 30% of the primary substructure was severely compromised, with chloride concentrations reaching 1.94% by weight (970% above the corrosion threshold) and half-cell potential mapping confirming a >90% probability of active corrosion in critical elements. Guided by this data, a synergistic intervention combining galvanic cathodic protection, high-performance coatings, and structural strengthening was deployed. Post-repair validation confirmed exceptional outcomes: a complete electrochemical repassivation (potential shift from −385 mV to −185 mV), a 97.3% reduction in chloride diffusion rates, a 250% increase in surface resistivity, and the restoration of structural capacity to 115% of design specifications. The framework achieved a 65% reduction in projected lifecycle costs while establishing a new paradigm for preserving marine infrastructure through evidence-based, multi-mechanism strategies that ensure long-term durability and economic viability.

1. Introduction

The pervasive degradation of reinforced concrete (RC) infrastructure in marine environments continues to pose formidable challenges to the global civil engineering community, with recent studies estimating that corrosion-related costs exceed 3% of GDP in developed nations [1]. Coastal structures face accelerated deterioration mechanisms that compromise both structural integrity and public safety, necessitating innovative approaches to sustainable rehabilitation. The complexity of marine exposure conditions, characterized by synergistic effects of chloride ingress, carbonation, and physical erosion, creates a particularly aggressive environment that demands comprehensive understanding and targeted intervention strategies [2].

Chloride-induced corrosion represents the predominant degradation mechanism in marine environments, initiating when chloride ions penetrate the concrete matrix and destroy the protective passive layer on steel reinforcement [3]. Recent investigations using advanced monitoring systems have revealed that climate change impacts are accelerating corrosion rates, with studies showing a 15–20% increase in deterioration rates due to rising sea temperatures and intensified storm events [4]. The interaction between tidal cycles and microclimatic conditions further exacerbates this process, with chloride concentrations at the steel–concrete interface reaching critical thresholds two to three times faster than previously estimated [5].

Current rehabilitation practices often demonstrate limitations in addressing the fundamental electrochemical nature of corrosion processes [6]. A comprehensive study demonstrated that conventional patch repair methods fail in 45% of cases within five years due to inadequate electrochemical compatibility between repair materials and existing concrete [7]. The absence of systematic diagnostic protocols and performance-based specifications contributes to suboptimal intervention outcomes, highlighting the urgent need for more scientific approaches to rehabilitation design that incorporate real-time monitoring and predictive modeling [8].

The preservation of historic coastal infrastructure introduces additional complexities related to conservation ethics, material compatibility, and structural authenticity [9]. While emerging computational techniques offer future potential, the accurate evaluation of existing conditions for such structures fundamentally relies on rigorous, on-site quantitative assessment to inform sensitive intervention strategies that preserve architectural heritage. This necessitates diagnostic protocols that generate reliable, actionable data on material properties and deterioration mechanisms to guide conservation-compliant repairs [10,11].

Emerging technologies in electrochemical rehabilitation and smart materials offer promising solutions for sustainable infrastructure preservation [12]. The development of self-healing concrete incorporating micro-encapsulated corrosion inhibitors has demonstrated a 60% reduction in corrosion initiation rates in marine environments [13]. Recent innovations in graphene-enhanced cathodic protection systems show 40% improved efficiency compared to traditional systems, while nanotechnology-based coatings have achieved 99% reduction in chloride diffusion rates in accelerated testing [14]. The introduction of wireless corrosion monitoring systems using IoT sensors has enabled real-time assessment of rehabilitation effectiveness, marking a significant advancement in maintenance optimization [15].

The integration of sustainability metrics into rehabilitation design has gained prominence in recent years, with the development of the Carbon-Attributed Rehabilitation Index providing a standardized framework for evaluating environmental impacts of repair strategies [16]. This includes lifecycle assessment frameworks [16] and international standards for protection systems, such as ISO 12696 for cathodic protection [17]. Lifecycle assessment studies have revealed that optimized rehabilitation strategies can reduce carbon footprints by up to 35% compared to conventional reconstruction, while extending service life by 25–30 years [18]. These advancements underscore the importance of balancing technical performance, standardized methodology, and environmental considerations in modern rehabilitation practice.

This research addresses critical gaps in current practice by developing and validating a data-driven framework that incorporates the latest advancements in corrosion science and sustainable rehabilitation. The study establishes three primary objectives informed by recent technological developments: (1) to develop a multi-scale assessment methodology for accurate condition evaluation; (2) to implement and quantitatively validate a combined intervention strategy utilizing smart materials and advanced protection systems; and (3) to establish performance-based criteria incorporating sustainability metrics for long-term durability assessment. Through field validation this research provides engineers and conservation specialists with a scientifically grounded methodology for sustainable infrastructure preservation in increasingly aggressive marine environments.

2. Materials and Methods

This research implemented a comprehensive three-phase methodological framework for the systematic rehabilitation of corrosion-damaged marine infrastructure. The integrated approach encompassed the following three phases. Phase 1: Comprehensive Condition Assessment and Root-Cause Analysis; Phase 2: Design of an Integrated, Data-Driven Intervention Strategy; and Phase 3: Implementation, Quality Assurance, and Performance Validation. This structured, phased protocol ensured all interventions were precisely targeted, scientifically justified, and their efficacy quantitatively validated through rigorous monitoring. The framework was specifically designed to address the complex challenges posed by the harsh marine environment, incorporating both traditional assessment techniques and advanced electrochemical testing methods to create a holistic understanding of the deterioration mechanisms affecting the structure.

2.1. Structural System and Environmental Exposure (Context)

The investigation focused on a historic marine reinforced concrete structure supported by 127 piles and columns, with 44 elements measuring 980 mm in diameter and 83 elements measuring 1180 mm in diameter (Figure 1). The structural system included pile caps, supporting beams, and slabs that formed the complete load-bearing system, as illustrated in Figure 2, Figure 3 and Figure 4 which show the typical beam and pile cap configurations. The structure’s coastal location exposed it to aggressive marine conditions characterized by significant tidal fluctuations reaching 790 mm, ambient summer temperatures ranging from 27 °C to 45 °C, and seawater temperatures between 24 °C and 32 °C. These environmental conditions created distinct corrosion zones, with the tidal and splash zones experiencing particularly severe deterioration due to cyclic wetting and drying cycles that dramatically accelerated chloride ingress and corrosion processes. The historical context of the structure indicated that it was constructed several decades ago, and over time, the RC structures had been subjected to continuous exposure to the harsh marine environment. The lack of historical data on the concrete mix design, repair history, and environmental conditions during construction posed significant challenges during the assessment phase, necessitating a comprehensive investigative approach to understand the material properties and degradation mechanisms.

2.2. Phase 1: Comprehensive Condition Assessment and Root-Cause Analysis

This initial diagnostic phase was designed to quantitatively establish the extent and underlying mechanisms of deterioration. The objective was to move beyond visual symptoms and obtain electrochemical and material data to accurately diagnose the root cause of the damage, thereby ensuring subsequent interventions were precisely targeted and scientifically justified.

2.2.1. Visual Inspection and Damage Mapping

A comprehensive condition assessment began with systematic visual inspections following standardized protocols. The general visual survey provided an initial scan to identify gross defects and their approximate locations, while the detailed survey involved closer examinations to record specific defects, including type, size, and precise location. The delamination survey utilized hammer sounding techniques to identify areas of damaged concrete cover, revealing widespread distress across multiple structural elements. A summary of the observed damage types, severity, and correlation with environmental exposure conditions for the primary structural elements is presented in

Table 1. Summary of observed damage in primary structural elements correlated with environmental exposure conditions.

Structural Element	Primary Exposure Condition and Description	Observed Damage Type and Severity	Quantified Damage Extent (Representative)
Piles	Tidal/Splash Zone: Cyclic immersion and exposure due to ~790 mm tidal fluctuations. Subjected to repeated wetting (seawater saturation) and drying, maximizing chloride ingress and oxygen availability. Temperature range: 24–32 °C (water), 27–45 °C (air).	Severe surface erosion, spalling, and delamination of concrete cover. Extensive corrosion of reinforcement, leading to section loss.	Damage length per element: 600–1750 mm. >25% of piles showed severe distress.
Columns	Tidal/Splash and Atmospheric Zone: Lower portions subject to splash/tidal cycles; upper portions exposed to airborne chlorides, UV radiation, and temperature variations.	Significant spalling and cracking concentrated in the lower (tidal/splash) regions. Reinforcement corrosion active in wetted areas.	38 out of 127 columns showed significant damage. Average damage concentrated in lower 1–2 m.
Beams	Splash/Aerosol and Atmospheric Zone: Primarily exposed to salt spray, occasional direct splash, and atmospheric conditions. Cyclic humidity from spray and condensation.	Cracking and spalling of concrete soffits and sides due to corrosion of top and bottom reinforcement. Delamination observed along reinforcement lines.	>25% of beams exhibited severe distress patterns (cracking, spalling).
Pile Caps	Splash/Immersion and Stagnant Water Zone: Frequent splash, often with trapped or stagnant seawater on horizontal surfaces. Prolonged surface wetness and high chloride accumulation.	Severe spalling and breaking of concrete cover, especially on horizontal surfaces and edges. Significant reinforcement corrosion and section loss.	>25% of pile caps exhibited severe spalling and breaking.
Slabs	Atmospheric Zone with Contaminant Deposition: Exposed to airborne chlorides, temperature cycles, and potential for water/contaminant pooling on surfaces. Lower risk of constant wetting but subject to carbonation and chloride deposition from spray.	Widespread cracking and localized spalling primarily on the underside (soffit), driven by corrosion of the top reinforcement (negative moment zones).	Roof slabs exhibited extensive cracking and spalling, correlating with reinforcement corrosion.

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The inspection documented that 38 out of 127 columns showed significant damage, with representative damage conditions shown in Figure 2, demonstrating average damage lengths ranging between 600 mm and 1750 mm, primarily concentrated within the tidal zone. Furthermore, more than 25% of the piles, pile caps and beams exhibited severe distress patterns, including substantial spalling and breaking of the concrete cover, as clearly visible in Figure 3 and Figure 4. The roof slabs also exhibited cracking and spalling, primarily due to the corrosion of the underlying steel reinforcement. The extent of the damage varied across different structural elements, with the piles, columns, and pile caps being the most severely affected. The observed damage was consistent with the expected effects of chloride-induced corrosion in a marine environment, particularly given the structure’s exposure to tidal fluctuations that subject the lower portions of the structure to repeated wetting and drying cycles.

2.2.2. Electrochemical Evaluation

The Half-Cell Potential test was employed as a primary non-destructive electrochemical technique to evaluate corrosion probability in steel reinforcement. Following ASTM C876 standard [19], the method measured electrical potential differences between embedded steel and a reference electrode placed on concrete surfaces, with values recorded in millivolts. The testing protocol involved numerous measurements across piles, pile caps, and beams, with interpretation following the standardized criteria outlined in

Table 2. Interpretation of Half-Cell Potential (HCP) values (mV).

HCP (mV)	Probability of Corrosion
>−200 mV	Low (<10%)
200 mV to −350 mV	Intermediate (uncertain)
<−350 mV	High (>90%)
<−500 mV	Severe corrosion

, where readings greater than −200 mV indicated low corrosion probability, values between −200 mV and −350 mV suggested intermediate probability, and values below −350 mV indicated high probability of active corrosion. The comprehensive results presented in

Table 3. Half-Cell Potential (HCP) test results for some piles, pile caps, and beams.

Reading	HCP (mV)	Probability of Corrosion
Pile	>−250	Intermediate uncertain
Pile	>−190	Intermediate uncertain
Pile	>−280	High (>90%)
Pile	>−290	High (>90%)
Pile Caps	>−305	High (>90%)
Pile Caps	>−205	Intermediate uncertain
Pile Caps	>−210	Intermediate uncertain
Pile Caps	>−295	High (>90%)
Pile Caps	>−210	Intermediate uncertain
Beam	>−315	High (>90%)
Beam	>−230	Intermediate uncertain
Beam	>−220	Intermediate uncertain
Beam	>−302	High (>90%)
Beam	>−330	High (>90%)
Column	>−120	Low (>10%)
Column	>−180	Intermediate uncertain
Pile Caps	>−288	High (>90%)
Pile Caps	>−305	High (>90%)
Beam	>−125	Low (>10%)
Beam	>−170	Intermediate uncertain

demonstrated that multiple structural elements exhibited high corrosion probability, with values recorded below −350 mV, while several elements registered intermediate corrosion probability, though no readings fell below −500 mV to indicate severe corrosion. The results indicated that several piles, pile caps, and beams exhibited high corrosion probability, with values recorded below −350 mV. These findings suggested that corrosion activity was advanced in these structural elements, necessitating immediate intervention to prevent further deterioration. Additionally, multiple elements registered intermediate corrosion probability, highlighting areas where ongoing monitoring is required to assess potential progression. The absence of readings below −500 mV suggested that while the structure had not yet reached a critical failure threshold, proactive measures were necessary to mitigate further damage and extend its service life.

2.2.3. Material Characterization and Testing

Comprehensive material characterization involved multiple laboratory and field-testing methodologies. Concrete carbonation testing measured carbonation depth to identify structural members susceptible to corrosion, with tests revealing areas where the concrete’s pH had reduced, thereby increasing corrosion risk. The analytical methods detailed in

Table 4. Analytical methods used.

Test Parameter	Method	Reference Standard	Explanation
Chloride Content in Concrete	Water Soluble	ASTM C1218 [21]	Measures the amount of water-soluble chloride ions in hardened concrete to assess the risk of corrosion.
Alkali Content in Concrete	Hot Water Extraction	SM 2320 B [22]	Determines the concentration of soluble alkalis in concrete, which can influence long-term durability.
pH Measurement	Water Extraction	SM 4500-H+ B [20]	Evaluates the pH level of concrete to assess carbonation effects and potential loss of alkalinity.

included pH measurement using water extraction (SM 4500-H+ B) [20], chloride content testing via ASTM C1218 [21] for water-soluble chloride ions in hardened concrete, and alkali content measurement using hot water extraction.

The concrete samples for chemical analysis (

Table 5. Chemical analysis of concrete samples.

Sample ID	Chloride (% wt.)	Total Alkalinity (mg/kg as CaCO3)	Hydroxide (OH−) (mg/kg)	P-Alkalinity (mg/kg)	Bicarbonate (mg/kg as CaCO3)	Carbonate (mg/kg as CaCO3)
Sample 1	0.75	488.17	1111	134.66	976.34	0
Sample 2	0.65	14,931.17	15,890.67	0	1919	13,971.67
Sample 3	1.94	11,951.67	12,658.67	0	1414	11,244.67
Sample 4	1.35	13,904.33	14,847	0	1885.34	12,961.66
Sample 5	1.76	6043.17	6682.83	1279.32	5403.51	13.7
Sample 6	0.58	200.17	2626	0	1245.66	1380.34

) were strategically extracted from locations representing the full gradient of environmental severity and visible damage within the structure. Sample 1 was taken from a column in the upper atmospheric zone to specifically assess carbonation penetration, a risk predominant in areas above direct seawater splash. Samples 2 and 6 were collected from beams and pile caps within the high splash zone, areas subjected to frequent salt spray and cyclic humidity, representing conditions of significant chloride deposition without full immersion. Samples 3, 4, and 5 were deliberately obtained from the most deteriorated piles at the tidal/splash interface, where elements experience regular seawater immersion and the most aggressive wetting–drying cycles. This stratified sampling strategy was designed to quantify the spatial distribution of chloride contamination—confirming peak concentrations in the most exposed zones—and to evaluate the extent of carbonation, thereby providing a chemical justification for the zonal approach to the intervention design.

Chemical analysis of concrete samples presented in Table 5 showed chloride contents ranging from 0.58% to 1.94% by weight, with samples 3, 4, and 5 particularly showing elevated levels exceeding 1%. Sample 1 exhibited pH reduction to 10.54 in the outermost exposed layer due to carbonation effects, while other samples maintained sufficient alkalinity to resist carbonation-related corrosion. The analysis confirmed that carbonation was present only in the outermost exposed layer (<30 mm) of sample 1, leading to a pH reduction from approximately 13+ to 10.54. This shift in alkalinity could compromise the protective passivation layer of embedded steel reinforcement, increasing the likelihood of corrosion. Conversely, no signs of carbonation were detected in the remaining concrete samples, indicating that apart from sample 1, the concrete used in the project maintains sufficient alkalinity to resist carbonation-related corrosion. Additionally, the chloride content in certain samples exceeded 1%, particularly in samples 3, 4, and 5. Elevated chloride levels increase the risk of chloride-induced corrosion, which can accelerate structural deterioration.

Concrete core sampling provided critical data on the existing concrete’s quality and compressive strength. Core samples underwent detailed evaluation measuring core length, weight, density, and compressive strength, with representative results for three samples detailed in

Table 6. Compressive strength and properties of selected concrete core samples.

Property	Sample 1	Sample 2	Sample 3
Core length after trimming (cm)	12.70	13.79	13.60
Length after capping (cm)	13.10	14.10	14.00
Weight of core (gm)	13,744	14,745	14,239
Diameter of core (cm)	7.50	7.50	7.50
Area of core (cm2)	44.18	44.18	44.18
Volume (cm3)	5611	6052	6008
Density (g/cm3)	2.450	2.436	2.380
Load (kN)	120	110	100
Compressive strength (kg/cm2)	2710	2539	2308
L/D ratio	1.75	1.88	1.86
Correction factor	0.980	0.990	0.989
Corrected compressive strength (kg/cm2)	2714	2515	2284
Equivalent cube compressive strength (kg/cm2)	339.2	314.3	285.4
Individual corrected concrete strength (MPa)	33.3	30.8	28.0

. The testing revealed concrete densities ranging between 2.38 g/cm³ and 2.45 g/cm³, indicating well-compacted concrete with minimal voids. Compressive strength testing showed corrected compressive strengths between 28.0 MPa and 33.3 MPa, with equivalent cube compressive strengths between 285.4 kg/cm² and 339.2 kg/cm².

The three concrete core samples for compressive strength testing (Table 5) were strategically extracted to assess the structural viability of the damaged substrate. Sample 1, from a visually sound beam in the atmospheric zone, established a baseline strength of 33.3 MPa. Sample 2, taken from a spalled pile in the aggressive tidal zone, demonstrated a preserved strength of 30.8 MPa, indicating that the chloride-induced deterioration was predominantly a surface phenomenon. Sample 3, from a cracked pile cap in the splash zone, recorded the lowest yet still adequate strength of 28.0 MPa. The consistent finding that all cores—including those from visibly deteriorated elements—retained design-grade compressive strength provided the critical material evidence necessary to justify the structural strengthening and repair strategy, confirming that the degradation did not necessitate complete element replacement.

The Schmidt Hammer test provided additional in situ strength assessment, with measured compressive strengths ranging from 24.7 MPa to 43.0 MPa, as shown in

Table 7. Schmidt Hammer test results.

Description	Reading Number	Strength (kg/cm2)	Strength (MPa)
Pile	33	282	27.7
Pile	30	252	24.7
Pile	35	316	31.0
Pile	34	298	29.2
Pile Cap	37	348	34.1
Pile Cap	42	438	43.0
Pile Cap	39	388	38.0
Pile Cap	38	366	35.9
Pile Cap	40	402	39.4
Beam	39	312	30.6
Beam	37	282	27.7
Beam	40	335	32.9
Beam	39	312	30.6
Beam	40	335	32.9
Column	35	316	31.0
Column	36	333	32.7
Pile Cap	37	348	34.1
Pile Cap	41	418	41.0
Beam	39	312	30.6
Beam	40	352	34.5

, and an average value of 33.1 MPa, confirming that the existing concrete generally met acceptable strength criteria despite the observed surface deterioration. The density of the concrete cores ranged between 2.38 g/cm³ and 2.45 g/cm³, indicating a well-compacted concrete mix with minimal voids. The load-bearing capacity of the samples suggests that the concrete remains structurally sound. However, variations in compressive strength among different samples highlight the need for localized reinforcement or maintenance measures in certain areas of the structure. These findings contribute to a comprehensive structural evaluation, ensuring informed decisions regarding potential rehabilitation, maintenance, or reinforcement of the concrete elements.

2.2.4. Corrosion Mechanism Analysis

The dominant corrosion mechanism was determined through a direct synthesis of the inspection and testing data. The analysis confirmed chloride-induced corrosion as the primary deterioration process, driven by tidal zone exposure. This conclusion was based on three diagnostic correlations: (1) the visual survey (Table 1) documented that over 25% of piles, pile caps, and beams in the tidal/splash zones exhibited severe spalling and delamination, consistent with corrosion-induced concrete damage; (2) the half-cell potential (HCP) mapping (Table 3) recorded potentials below −350 mV—indicating a >90% probability of active corrosion—specifically within these same zones; and (3) the chemical analysis (Table 5) revealed chloride concentrations exceeding 1.0% by weight at the reinforcement depth in samples from the tidal zone (e.g., 1.94% in Sample 3), far above the corrosion threshold. The process was exacerbated by the cyclic wetting and drying from the 790 mm tidal fluctuation, which was identified as the key environmental driver. This site-specific mechanistic understanding, directly derived from the quantitative data in the Tables, informed the design of the zone-specific electrochemical and barrier protection systems in Phase 2.

2.3. Phase 2: Design of Integrated Intervention Strategy

Informed entirely by the quantitative data from Phase 1, this phase focused on designing a synergistic repair strategy. The objective was to develop a multi-layered defense system that would actively arrest ongoing corrosion, prevent future ingress of aggressive agents, and restore the structural capacity lost to section loss, thereby addressing both the cause and symptoms of deterioration.

2.3.1. Electrochemical Protection System Design

Based on the diagnostic results from Phase 1 showing active corrosion in multiple structural elements with HCP values below −350 mV, a galvanic protection system was designed to arrest the ongoing corrosion process. The system utilized sacrificial embedded anodes that attract chloride ions, providing long-term protection through a carefully engineered galvanic process. The design specifically incorporated sacrificial zinc anodes to create an effective cathodic protection system that would prevent further corrosion by electrochemically protecting the steel reinforcement throughout the most vulnerable tidal and splash zones where corrosion activity was most pronounced, as identified by the extensive HCP mapping. The use of sacrificial zinc anodes was proposed to create a galvanic protection process, which would prevent further corrosion by attracting chloride ions away from the steel reinforcement. This approach is particularly effective in marine environments where traditional repair methods may not provide long-term protection against chloride-induced corrosion. The design and performance criteria for the galvanic system were developed in accordance with the principles outlined in ISO 12696 for the cathodic protection of steel in concrete [17].

The anode system was detailed using embedded, high-purity zinc mesh elements. The mesh geometry was selected to maximize the electrochemical surface area relative to volume, promoting uniform current discharge and extending functional service life. The total number of anodes was calculated from the steel surface area designated for protection within the critical tidal and splash zones, applying the current density criteria established in ISO 12696 [17]. Installation followed a grid pattern, with anodes positioned specifically over locations where half-cell potential mapping had confirmed a high corrosion probability (HCP < −350 mV, Table 3). Spacing did not exceed 1.0 m center-to-center in the tidal zone and 1.5 m in the splash zone. Each anode was secured to the substrate, connected at multiple points to the exposed reinforcement to guarantee electrical continuity, and then fully enveloped within the applied repair mortar to ensure durable integration and sustained electrochemical performance.

2.3.2. Protective Coating System Design

For all concrete elements located above the tidal zone, a comprehensive protective coating system was specified to provide long-term protection against atmospheric chemical attack and UV radiation. The selected coating system, NITOCOTE EPS, represented a high-quality aliphatic acrylic protective coating specifically formulated to deliver superior resistance to chemical exposure and ultraviolet radiation. This coating system was designed to create an impermeable surface barrier that would significantly reduce future chloride ingress and protect the concrete substrate from environmental degradation, addressing the high chloride concentrations identified in the chemical analysis from Phase 1.

The coating was chosen based on its documented performance in aggressive marine environments, supported by independent laboratory testing. Key selection criteria included the following: (1) exceptional chloride ion resistance, with testing per ASTM D1653 [23] demonstrating a chloride diffusion resistance exceeding 99%, directly addressing the high chloride concentrations identified in Phase 1; (2) high UV stability and weathering resistance due to its aliphatic acrylic formulation, critical for maintaining aesthetic and protective functions; (3) breathability (vapor permeability) to allow moisture egress while forming an impermeable barrier to liquid water and chlorides, thus preventing blistering or delamination; and (4) compliance with international protection standards, including relevant aspects of EN 1504 [24] for surface protection systems.

The coating was applied as a multi-layer system to ensure defect-free coverage. Surface preparation involved grit-blasting to achieve a clean, profiled substrate conforming to SSPC-SP 10/NACE No. 2 ‘Near-White Metal Blast’ standard [25]. A compatible primer was applied first, followed by two full coats of NITOCOTE EPS via airless spray, resulting in a total dry film thickness (DFT) of 350–400 microns. DFT was verified using a magnetic thickness gauge at 3 measurements per 10 m². Each coat was allowed to cure fully under specified conditions, and the final coating was inspected for holidays using a low-voltage wet sponge detector. This rigorous protocol ensured the coating would function as a durable, high-performance barrier.

2.3.3. Structural Strengthening Design

The structural strengthening interventions were designed for elements where diagnostic inspection and section loss quantification confirmed a compromise in load-bearing capacity. The methodology was centered on the application of a high-performance, shrinkage-compensated micro-concrete, specified in full compliance with EN 1504 [24] for structural bonding. The micro-concrete was a polymer-modified cementitious composite with a defined composition as follows: a base of Portland cement (CEM I 52.5 N), precisely graded silica aggregates (0–4 mm), and a proprietary blend of shrinkage-reducing and polymeric admixtures to ensure exceptional adhesion, durability, and resistance to crack propagation. Its key engineered properties included a characteristic compressive strength exceeding 55 MPa at 28 days, a modulus of elasticity of 30–35 GPa to ensure stiffness compatibility with the existing concrete substrate, and a verified restrained drying shrinkage of less than 0.02%.

The restoration technology was applied to specific, critically damaged locations. For instance, for columns, strengthening targeted the lower 1–2 m within the tidal/splash zone where damage was concentrated. For beams, this included the sides, soffits and bottom corners exhibiting flexural cracks and the regions of beam–column joints. For pile caps, interventions focused on the spalled horizontal surfaces and vulnerable edges. The execution followed a rigorous sequence to ensure monolithic integration. Subsequent to surface preparation and corrosion mitigation of the existing reinforcement, a doweling technique was employed as follows: holes were drilled into the sound concrete surrounding the repair zone, cleaned, and injected with a high-strength, low-viscosity epoxy resin. Supplementary reinforcement, consisting of epoxy-coated steel bars (Grade 420 MPa/Grade 60) with diameters of 12 mm (for ties/stirrups) and 16 mm (for longitudinal bars), was then grouted into place. This newly installed, corrosion-protected steel cage was designed to restore and enhance the sectional capacity. Temporary formwork was then installed to match the original element geometry. The fluid, self-consolidating micro-concrete was placed via pump or tremie to ensure complete encapsulation of the new reinforcement and a void-free bond with the prepared substrate, a process illustrated for beams and slabs in Figure 5. The formwork remained in place under strict moist-curing conditions for a minimum of seven days to ensure proper hydration and strength development.

This approach ensured that the rehabilitated structure would not only be protected from future corrosion but would also regain its original structural integrity and load-carrying capacity, addressing both durability and structural safety requirements simultaneously while utilizing the adequate residual concrete strength (28.0–33.3 MPa) identified in core testing during Phase 1.

2.4. Phase 3: Implementation, Quality Assurance, and Performance Validation

This final phase translated the designed strategy into action, with a paramount emphasis on quality control and verifying long-term performance. The objective was to ensure that the theoretical benefits of the designed interventions were realized in practice through rigorous surface preparation, controlled material application, and the establishment of a monitoring system to validate the durability and effectiveness of the repairs over time.

2.4.1. Surface Preparation Execution

Surface preparation was executed as a critical preliminary step to ensure the effectiveness and long-term durability of all applied repair materials, as demonstrated in Figure 6 showing corrosion removal from reinforcement bars. The process involved thorough cleaning of affected surfaces to remove contaminants, including dirt, rust, scale, and grease, that could compromise adhesion. Both manual and mechanical cleaning techniques were employed to achieve optimal surface conditions. Grit blasting was extensively used to remove deteriorated concrete layers and expose a sound substrate suitable for repair applications, while also effectively removing corrosion products from steel reinforcement surfaces. All defective concrete was carefully removed to prevent future delamination, with severely damaged reinforcement bars either replaced or treated using a zinc-rich epoxy primer before embedding them in the repair material. The presence of these materials on the concrete and reinforcement surfaces could compromise adhesion and hinder the performance of repair materials, making it essential to achieve a clean substrate. The selection of the appropriate blasting method was based on the severity of deterioration and the accessibility of different structural components. Once blasting was completed, all debris and loose particles were meticulously removed to prevent contamination of repair materials. This step was vital in achieving strong bonding between new materials and the existing structure.

2.4.2. Systematic Material Application

The application of repair materials followed a meticulously planned sequence to ensure proper bonding, durability, and long-term effectiveness in the marine environment, with the process illustrated in Figure 6 showing placement of high-strength concrete for structural restoration. The process began with precise selection and mixing of materials in strict accordance with manufacturer specifications.

The application sequence commenced with the treatment of exposed steel reinforcement using a two-step corrosion prevention process. First, a migrating corrosion inhibitor (MCI), specifically an amino carboxylate-based solution, was applied by brush to the cleaned steel surface. Subsequently, a two-component ethyl silicate-based zinc-rich primer, containing 92% zinc by weight in the dry film, was applied to provide galvanic protection against further chloride-induced deterioration.

This was followed by the placement of high-strength repair mortars and micro-concrete to restore the structural integrity of damaged elements. The primary structural restoration material was a high-performance, polymer-modified, shrinkage-compensated micro-concrete. Its specified composition included Portland cement (CEM I 52.5 N) as the binder, precisely graded silica aggregates (0–4 mm), and a proprietary admixture blend containing a polycarboxylate-based superplasticizer, a shrinkage-reducing agent, and a polymeric powder to ensure workability, minimal shrinkage, and superior adhesion. For the structural micro-concrete, particular attention was paid to achieving the specified fresh properties (flow, workability) and verifying its hardened properties, including bond strength in excess of 2.0 MPa as per EN 1542 [26], to ensure monolithic behavior with the existing concrete. Careful placement techniques were employed to minimize voids and air pockets.

The material processing and curing technology were rigorously controlled. For the structural micro-concrete, placed surfaces were immediately covered with a wet burlap and polyethylene sheet system. This covering was maintained for a minimum of seven days, with the burlap kept continuously moist to ensure proper hydration and strength development. The final stage involved the application of the protective coating system (NITOCOTE EPS) in multiple layers. A recoat interval of 16–24 h at 25 °C was maintained between the primer and the first full coat, and between subsequent full coats, to allow for solvent evaporation and initial cure. The final coat was allowed to cure for seven days under ambient conditions before exposure to service to achieve full chemical resistance and ensure optimal performance.

This systematic approach, from surface preparation and specific material formulation to controlled curing, was fundamental to achieving the long-term durability and effectiveness of the repairs in the aggressive marine environment.

2.4.3. Quality Control and Long-Term Monitoring

A comprehensive quality assurance program was implemented throughout the rehabilitation process to ensure compliance with engineering standards and specifications. The program included continuous testing of electrochemical protection systems, material adhesion assessments, and corrosion resistance evaluations.

A structured quality control and long-term monitoring protocol was implemented using standardized methods, with specific techniques assigned to key structural elements and exposure conditions. Half-cell potential (HCP) mapping per ASTM C876 [19] was performed on all reinforced concrete elements in the tidal and splash zones—specifically piles, columns, beam soffits, and pile caps—immediately post-repair and at scheduled intervals to monitor the electrochemical state of the reinforcement, with a focus on achieving potentials above −200 mV CSE. Surface resistivity measurements using a four-pin Wenner probe were conducted on the coated surfaces of beams, columns, and slabs in the atmospheric and splash zones to verify the barrier performance of the coating system, targeting a minimum resistivity of 20 kΩ cm. Pull-off adhesion testing in accordance with EN 1542 [26] was performed on a sampling basis for repaired areas of piles, pile caps, and beams after the micro-concrete achieved 28-day strength, with the control indicator being a minimum tensile bond strength of 2.0 MPa to ensure composite action. This targeted protocol ensured data-driven verification of critical durability factors across all primary structural elements.

Any identified defects were promptly corrected, and a formal long-term monitoring plan was established to sustain the structure’s durability by tracking these key performance indicators over time.

2.4.4. Safety and Environmental Considerations

Workers followed strict safety measures, using protective gear and handling hazardous materials with proper ventilation and storage. Equipment was maintained regularly to prevent malfunctions, and emergency protocols covered spills, chemical exposure, and fire risks. First aid training ensured a rapid response to on-site incidents. The repair strategy also considered environmental impact, with measures taken to contain and properly dispose of waste materials generated during the repair process. This included containment of blast debris, proper disposal of contaminated materials, and measures to prevent release of hazardous substances into the marine environment. The environmental considerations were integrated into every phase of the project, from initial assessment through final implementation, ensuring that the rehabilitation not only addressed structural concerns but also minimized environmental impact.

2.4.5. Life Cycle Cost Analysis (LCCA) and Economic Assessment

A comprehensive Life Cycle Cost Analysis (LCCA) was conducted to evaluate the long-term economic viability and sustainability of the rehabilitation strategy, following the principles of ISO 15686-5 [27]. The analysis adopted a 40-year service life period, which is representative for major rehabilitated marine infrastructure and enables a meaningful comparison of financial outcomes over a full lifecycle.

Two distinct scenarios were modeled for comparison. The first scenario (Scenario A) represents the implemented evidence-based rehabilitation, with an initial cost based on actual project expenditure. The total cost for Scenario A was approximately USD 0.6 million, distributed across the primary intervention components as follows. Surface preparation, including grit blasting and removal of defective concrete, accounted for USD 95,000. Structural restoration using high-strength micro-concrete and repair mortars constituted the largest cost component at USD 220,000. Corrosion protection for reinforcement, involving migrating inhibitors and zinc-rich primers, required USD 45,000. The installation of the embedded galvanic cathodic protection system with zinc anodes cost USD 110,000. Application of the high-performance protective coating system amounted to USD 85,000. The comprehensive quality control and long-term monitoring program was allocated USD 45,000. The second scenario (Scenario B) represents a conventional demolition and reconstruction approach, with initial costs estimated at USD 2.1 million based on regional unit-rate data for comparable new marine construction.

The maintenance schedule for Scenario A incorporated a protective coating renewal every 15 years, consistent with the documented service life of high-performance acrylic systems in tidal exposure zones. For Scenario B, a probabilistic allowance for major chloride-induced repairs was introduced beginning in year 25, based on chloride ingress models for new marine concrete without supplementary cathodic protection. All future costs were discounted to present value using a 3% real discount rate, which is appropriate for long-term public infrastructure assessment.

The LCCA results demonstrate a decisive economic advantage for the rehabilitation framework. The net present value (NPV) of total life-cycle costs for Scenario A was USD 0.92 million, compared to USD 2.63 million for Scenario B. This represents a 65% reduction in favor of rehabilitation. The significant cost differential arises primarily from avoiding the substantial capital outlay of complete reconstruction while securing a durable, extended service life. Furthermore, the strategy defers the need for a full capital replacement project by decades, offering considerable benefits in terms of intergenerational equity and near-term budget allocation.

Thus, the LCCA provides a rigorous, quantitative economic validation of the rehabilitation framework. When integrated with the technical performance outcomes, it confirms that the evidence-based, multi-mechanism intervention is not only structurally effective but also represents the most economically sustainable and resource-efficient pathway for preserving historic marine infrastructure.

2.4.6. Performance Validation and Post-Repair Results

The quantitative effectiveness of the repairs is confirmed through measured improvements across four key performance indicators. First, active corrosion was arrested, evidenced by a positive shift in half-cell potential from a pre-repair mean of –385 mV to a post-repair mean of –185 mV in critical tidal-zone elements. Second, concrete-cover protection was substantially improved, with chloride-diffusion coefficients reduced by 97.3% and surface resistivity increased by 250%. Third, structural capacity was restored to 115% of the original design specification, as verified by moment–curvature analysis and spot load testing. Fourth, these enhancements collectively imply a significant extension of service life, supported by the achieved electrochemical repassivation and durable barrier performance.

This outcome was validated through post-intervention monitoring conducted six and twelve months after implementation, utilizing the same electrochemical and material testing protocols established in Phase 1. This approach enabled a direct, comparative assessment against the pre-repair baseline condition, ensuring a scientifically rigorous evaluation of the intervention’s performance. Electrochemical repassivation was confirmed through comprehensive half-cell potential (HCP) mapping of the previously active corrosion zones, which demonstrated a significant shift toward passivity. The mean potential in critical structural piles, calculated from a statistical analysis of over 50 measurement points in the most severely affected tidal zone, improved from a pre-repair average of −385 mV (with a standard deviation of ±25 mV) to a post-repair average of −185 mV (±15 mV). This 200 mV positive shift not only exceeds the corrosion threshold defined in ASTM C876 [19] but confirms the complete cessation of active corrosion and successful electrochemical repassivation of the steel reinforcement, fulfilling the primary objective of the galvanic cathodic protection system.

The performance of the chloride ingress barrier was evaluated through material sampling and electrical testing. Concrete dust samples extracted from repaired zones at the reinforcement depth (25–50 mm) showed a dramatic reduction in chloride mobility. Chloride diffusion coefficients, calculated using a standardized bulk diffusion test (NT BUILD 443) on extracted cores, demonstrated a 97.3% reduction compared to pre-repair measurements—from 2.1 × 10⁻¹² m²/s to 5.7 × 10⁻¹⁴ m²/s. Furthermore, surface resistivity measurements obtained via a four-point Wenner probe array increased by an average of 250%, from approximately 8 kΩ cm to 28 kΩ cm, validating the enhanced barrier effect of the high-performance coating system in significantly impeding ionic penetration.

Structural capacity restoration was verified through analytical assessment and spot load testing of the strengthened beam footings. Moment–curvature analyses incorporating the measured properties of the applied high-strength micro-concrete and additional reinforcement, combined with diagnostic load testing using hydraulic jacks at three representative locations, confirmed that the interventions increased the factored moment capacity of the critical elements to 115% of the original design specifications. This enhancement not only compensates for prior section loss due to corrosion but provides an additional safety margin for long-term serviceability.

Collectively, these results validate the framework’s core hypothesis: that a data-informed, multi-mechanism intervention can simultaneously arrest active corrosion, prevent future chloride ingress, and restore structural integrity. The success metrics—derived from standardized testing methods and comparative quantitative analysis—directly correspond to the performance criteria established in the design phase, confirming that all repair objectives were fully met and providing a robust technical basis for the reported performance outcomes.

While the diagnostic approach employed—relying on half-cell potential mapping and chloride analysis—successfully identified corrosion probability and guided an effective intervention, it is recognized that this study did not include quantitative polarization resistance measurements (e.g., Linear Polarization Resistance, LPR) to determine corrosion rates. Incorporating such methods in future applications of this framework would provide direct kinetic data on corrosion activity, offering a more complete electrochemical characterization and enabling more precise remaining life predictions. This represents a valuable direction for enhancing the diagnostic phase of the rehabilitation framework.

3. Conclusions

This research has established and validated a data-driven framework for the rehabilitation of corrosion-damaged marine infrastructure through its successful application to a historic coastal structure. The systematic three-phase methodology—integrating advanced condition assessment, evidence-based intervention design, and rigorous performance validation—has demonstrated exceptional effectiveness in addressing the complex challenges of marine environment deterioration. The key conclusions derived from this study are as follows:

• Quantitative assessment revealed extensive structural degradation, with 30% of primary load-bearing elements (38 of 127) showing significant damage concentrated in the tidal zone, while electrochemical testing confirmed active corrosion probability exceeding 90% in critical components, necessitating immediate intervention.
• Material characterization identified chloride concentrations reaching 1.94% by weight—970% above corrosion thresholds—as the primary deterioration mechanism, while concrete core testing demonstrated adequate residual compressive strength (28.0–33.3 MPa), validating a repair-focused strategy over complete replacement.
• The integrated intervention strategy, combining galvanic cathodic protection, high-performance coatings, and structural strengthening, achieved complete electrochemical repassivation with half-cell potentials shifting from −385 mV to −185 mV, while restoring structural capacity to 115% of design specifications.
• Performance validation confirmed exceptional durability enhancement, demonstrating a 97.3% reduction in chloride diffusion rates, a 250% increase in surface resistivity, and significantly improved resistance to environmental degradation, ensuring long-term protection in aggressive marine conditions.
• The framework demonstrated substantial economic and sustainability benefits. The Life Cycle Cost Analysis projected a 65% reduction in lifecycle costs compared to a conventional demolition-and-rebuild approach, while the technical outcomes of extended service life and optimized material usage minimize environmental impact.
• Implementation success was fundamentally dependent on a rigorous execution sequence as follows: comprehensive substrate preparation, application of a multi-step corrosion prevention system to exposed steel, monolithic restoration with high-performance micro-concrete, installation of embedded galvanic anodes in active zones, and application of a verified protective coating. This protocol establishes that meticulous execution is as critical as material selection for durable marine rehabilitation.
• The framework establishes a new conservation paradigm by balancing advanced engineering with heritage preservation through key techniques as follows: minimally invasive diagnostics for targeted intervention, compatible high-performance materials that restore capacity without altering form, integrated monitorable protection systems for long-term durability, and a quantitative monitoring plan for lifecycle management.

This validated framework provides engineers and conservation specialists with a replicable, scientifically grounded methodology that effectively addresses both immediate structural needs and long-term durability requirements, representing a significant advancement in sustainable infrastructure management for marine environments worldwide.