Aggressive Marine Environment Research Articles

Efficient and reliable corrosion control for subsea assets: challenges in the design and testing of corrosion probes in aggressive marine environments

Abstract This review discusses the challenges in designing and testing corrosion probes for aggressive marine environments. The objectives are to analyze existing literature, identify methodological problems, and highlight research gaps in subsea corrosion control. To achieve these, a comprehensive review of relevant literature was conducted, focusing on factors like high salinity, fluctuating temperatures, and the presence of corrosive agents. The methods involved synthesizing information from peer-reviewed articles, industry reports, and academic publications to thoroughly analyze current state of knowledge. The findings of this review highlight the need for standardized testing protocols, improved understanding of material compatibility, and consideration of real-world conditions in corrosion probe design and testing. Methodological problems include the lack of standardized testing protocols, limited understanding of material compatibility, and insufficient consideration of real-world conditions. These findings emphasize the challenges researchers and practitioners face in developing efficient and reliable corrosion control strategies for subsea assets. In terms of novelty and improvement, this manuscript contributes to improving corrosion control practices in aggressive marine environments by synthesizing existing literature, identifying methodological problems, and highlighting gaps. By addressing these challenges, future research can focus on developing innovative solutions and methodologies to enhance the durability and effectiveness of corrosion probes in subsea environments.

Flexural behaviour of the segmental precast concrete decks post-tensioned by GFRP rods

This paper introduces an innovative post-tensioned segmental concrete deck system internally reinforced and tied with GFRP reinforcements for application in pontoon decks and other deck structures in aggressive marine environments. Utilisation of the GFRP reinforcements in floating concrete structures is essential because of their non-corrosive characteristics. Six large-scale segmental decks following the specifications of Queensland maritime infrastructure were designed, manufactured, and tested to assess the reliability of the new construction system under static flexural loading in the flatwise and edgewise orientations. One segmental deck served as a reference with hand-tight post-tensioning, while the remaining specimens were connected by the GFRP rods with varying levels of post-tensioning. All decks were tested up to failure, allowing for an investigation of their flexural strength, load-strain behaviour, joint opening, and failure mechanism. The results showed that post-tensioning the GFRP rods improves the flexural performance of the segmental decks. The higher the level of post-tensioning, the higher the contact area between the segments at the joint is achieved. A numerical model was developed to understand the detailed mechanism of both flatwise and edgewise specimens. A strain reduction coefficient in the segmental concrete deck under flexure is introduced accounting for the joint presence to reliably calculate the stress in the post-tensioned internal GFRP rod when the concrete in the joint crushes. The system investigated can increase maritime and recreational infrastructure's construction efficiency and provide creative solutions in the GFRP-reinforced concrete structures in the building and construction industry.

50 Years Of Hanbar Concrete Units In Australia And New-Zealand: Lessons Learned From Physical Modelling Studies And Recently Built Structures

During the last 50 years, numerous breakwaters along the eastern coast of Australia, and more recently in New Zealand, have undergone construction, repairs, or upgrades using Hanbar concrete armour units. These units are distinct to Australasia, and there is limited information about their properties in standard coastal engineering literature. This paper first provides a survey and timeline of all known projects using Hanbars. An overview of the Hanbar concrete unit features and manufacturing method is then provided. The paper presents a summary of results of previous modelling studies of Hanbar applications to specific breakwaters, as well as recent research programs completed at WRL, and provides placement density guidelines as well as recommended damage coefficient (Hudson Kd) for design. The paper concludes with a brief overview of two recent case studies which have successfully capitalized on the economical, robustness and manufacturing simplicity of the Hanbar concrete units. The first case study is on the Opotiki Harbour Development (“OHD”) in New Zealand. The OHD scheme comprises twin 400 m long training wall breakwaters to train a dynamic river mouth. A multi-stage approach to physical modelling was adopted by conducting 2D modelling of key sections of the training wall trunks, quasi-3D modelling of the breakwater head, and full 3D modelling of complete structures. The second case study presents the results of a field trial investigating the potential for high-density geopolymer concrete (GPC) coastal armour units. This resulted in the casting and placing of thirteen 16 t GPC Hanbar units (SG 2.6) on the Port Kembla northern breakwater in NSW. The trial proved the viability of production of geopolymer armour units, and allowed long-term monitoring of the integrity of the concrete in the aggressive marine environment.

Experimental behaviour of hybrid carbon steel – stainless steel bolted connections subjected to electrochemical corrosion

To minimise cost in practical applications whilst still obtaining a satisfactory performance, stainless steel is often employed in aggressive marine environments to ensure the durability of the structure, whilst parts of the structure less susceptible to corrosion employ conventional carbon steel. When the two materials are in direct contact in the connection region, galvanic corrosion can occur over time thus leading to an increased level of corrosion of the less noble carbon steel parts and an associated degradation in the structural performance. A comprehensive experimental study on the shear behaviour of hybrid carbon steel – stainless steel bolted connections subjected to electrochemical corrosion is presented in this paper. A total of 30 bolted connection specimens were designed and assembled from hot-rolled carbon steel and stainless steel plates. Two bolt grades, the high strength bolts 10.9 and the precipitation hardening stainless steel bolts 10.9 were used to connect the plates. Employing the electrochemical corrosion method, the specimens were subjected to various levels of corrosion by adjusting the duration over which the specimens were sunk in the corrosive medium, which resulted in both different corrosion morphology as well as different levels of mass loss of the carbon steel plates due to corrosion. The corroded connection specimens were thereafter tested to failure under shear exhibiting 4 different failure modes. The load versus deformation curves were recorded and are reported herein, whilst the observed failure modes were also documented. It was revealed that increased level of corrosions led to decreased levels of bolt pretention forces and ultimate resistances of the connections, albeit the severity of the degradation strongly depended on the adopted joint configuration and resulting failure mode.

Effect of Al Content on the Long-Term Corrosion Behavior of Arc-Sprayed ZnAl Alloy Coatings

The corrosion of steel structures in aggressive marine environments is a vital issue that induces significant degradation of their performance and lifespan. Herein, three arc-sprayed ZnAl coatings with varied Al contents of 0 wt.%, 15 wt.%, and 50 wt.% were deposited onto a hull steel substrate. The effect of Al content on the long-term corrosion protection performance of ZnAl coatings left in a chloride-containing solution for 840 h was systematically investigated. The evolutions of open-circuit potential, polarization curves, and electrochemical impedance spectroscopy of different ZnAl coatings during the long-term immersion test were examined. The morphologies and phase constitutions of the corrosion products were characterized. The results indicated that the corrosion rate of ZnAl coatings decreased as the Al content increased, and the ZnAl50 coating exhibited the most superior long-term corrosion protection performance. Moreover, for the three ZnAl coatings with an Al contents varying from 0 to 50%, their corrosion rate increased with immersion time in the initial 360 h due to the formation of the unstable and porous corrosion product ZnO; after 360 h immersion, their corrosion rate decreased with the prolonging of immersion time. This was revealed to be related to the formation of different corrosion products. ZnO and stable Al2O3 were the main corrosion products for the pure Zn coating and ZnAl15 coating, respectively. Al2O3 and powerful layered double hydroxide Zn6Al2(OH)16CO3·4H2O were found to be the dominant corrosion products of the ZnAl50 coating, which was responsible for its remarkable long-term corrosion protection performance.

Residual load-bearing capacity of corroded reinforced concrete columns with an annular cross-section

Reinforced concrete (RC) columns with an annular cross-section are commonly utilized as supporting structural members in ocean engineering structures, and their structural performance deterioration is mainly caused by the corrosion of rebar in aggressive marine environment. This paper proposes an effective method to investigate the effects of rebar corrosion on the structural performance of the annular RC columns under various loading conditions. Firstly, the material degradation and residual structural strength models are proposed based on the analysis of the corrosion-induced deterioration of RC structures. Then, the general method for determining the load-bearing capacity is developed using the equivalent steel ring assumption. To improve computational efficiency and practical applicability, an effective method for assessing the residual load-bearing capacity is proposed by simplifying the calculations of rebar load-bearing capacity coefficients using the regression fitting approach. Finally, the effectiveness of the proposed simplified method is demonstrated with the relevant experimental data available. The results show the capacity deterioration rate is strongly related to the corrosion level and loading condition with the most severe degradation typically at the corrosion level of 5–10%, and the smaller and larger eccentric columns drop the capacities by about 28% and 41% at 10% corrosion level, respectively.

Factorial Mixture Design for Properties Optimization and Modeling of Concrete Composites Incorporated with Acetates as Admixtures

Nowadays, admixtures are used with the aim to provide strength and durability to concrete with less water use. New and low-cost admixtures gained a large amount of consideration to mitigate the problems associated with concrete’s durability and service life without upsetting its strength properties. The current work investigates the effect of three types of acetates on the workability, density, and compressive strength of concrete, which is used in structures of the Iraqi ports that suffer from corrosion damages and deterioration owing to the aggressive marine environments. Potassium acetate (KA), calcium acetate (CaA), and ethyl acetate (EA) are incorporated with different doses (1.38–5.6 wt.% of cement) in concrete mixtures using different water/cement ratios (0.48–0.54) based on an espoused central composite experimental design. The experimental results confirmed that the average workability increased with increasing the acetate dose, particularly with CaA. The density and compressive strength of 28 days of water-cured mixtures increased with increasing acetate dose following the order: Ca > K > Ethyl acetate and decreased with increasing w/c ratio. The high rise in compressive strength and workability linked to control mixtures was 30.8% and 77.3% as well as 15.7% and 64.3% for the mixtures incorporated with 5.6 wt.% CaA and KA, respectively. While it was 14.2% and 58.3% for the mixtures incorporated with 3.5 wt.% EA. RSM was employed to optimize and model the design and hardened properties of concrete mixtures. ANOVA results predicted the same trend, which was obtained from the experimental results. The mathematical models were valued with high-regression coefficients. The highest compressive strength of 42.68 MPa has been achieved for a concrete mixture of 0.48 w/c ratio by the incorporation of 5.1 wt.% CaA through a model with R2 96.97%. The relatively low-cost acetate admixtures, particularly CaA, seemed promising for the fabrication of concrete with outstanding properties.

Performance-based seismic resilience and sustainability assessment of coastal RC bridges in aggressive marine environments

Corrosion-induced deterioration of material properties can noticeably affect the seismic performance of coastal reinforced concrete (RC) bridges in aggressive marine environments, causing significant adverse economic and environmental consequences post extreme events. This study systematically investigates the time-dependent seismic performance, resilience, and sustainability of coastal RC bridges. For that purpose, a three-dimensional (3D) nonlinear finite element (FE) framework is developed and combined with the formulation of performance-based earthquake engineering (PBEE) and an economic input-output life cycle assessment (LCA) approach. Seismic resilience and robustness of the coastal RC bridges are subsequently evaluated in terms of the post-earthquake repair cost, repair time, and carbon footprint quantified by CO2. Within this framework, additional analyses are conducted to explore possible retrofit measures, including the use of fiber-reinforced polymer (FRP) reinforcement on the sustainability and resilience of the retrofitted RC bridges. For the presented scenario, it is shown that wrapping bridge columns with FRP composites can effectively increase the moment capacity, thus improving resilience and sustainability by reducing as much as 650 Mg of CO2 for this specific bridge. Overall, the derived insights highlight the need for sustainability, resilience, and potential retrofit analysis of coastal RC bridges in seismically active regions affected by corrosion-induced deterioration.

MATERIALS AND ANTICORROSION DEVELOPMENTS IN OFFSHORE AND SUBSEA OIL AND GAS PRODUCTION

The development of hydrocarbon resources of the continental shelf of the Russian Federation and especially its Arctic part and the Far East is the largest infrastructure project based on unique proven oil and gas reserves. The continental shelf of Russia is a large national hydrocarbon reserve, which can provide up to 25% of Russian oil and up to 30% of Russian gas. The most difficult reserves represent difficult development conditions - high pressure and low temperatures, may be in deep water or arctic regions. As oil resources become more and more heterogeneous, an expansion of various methods of extraction and processing is required, including in extreme conditions, at high pressures in aggressive marine environments and low temperatures. An integrated field development method allows maintaining a high level of hydrocarbon production for a long time, reducing costs by optimizing the resources used and using a common infrastructure. In the long term, the presence of production facilities and service bases near the Arctic shelf will allow solving multidisciplinary tasks that affect various segments and areas, such as engineering and technology, environmental protection, and others. The review article discusses the factors affecting the resistance of oil and gas pipelines to corrosion in the marine environment, the issues of hardening and alloying corrosion-resistant alloys for use in the marine and underwater environment while expanding the boundaries of the use of traditional technical alloys, as well as further study of the mechanisms of corrosion and crack propagation, which can lead to equipment failure and destruction. The study of nanoscale corrosion analyzed in this article can have a profound impact on the degradation characteristics of materials applicable to the entire industry.

Article: Oxy-Nitriding AISI 304 Stainless Steel by Plasma Electrolytic Surface Saturation to Increase Wear Resistance

AISI 304 SS has good corrosion resistance in a variety of environments but does not have good resistance to wear. Aggressive marine environments require materials that can withstand both the biocorrosion and the wear associated with the impact of waves, ocean currents and suspended particles. Oxy-nitriding of stainless steels can be used to increase their hardness and wear resistance. The conventional oxy-nitriding process is lengthy, and the temperature involved can affect the corrosion resistance of the material. To mitigate these problems, it was decided to study an oxy-nitriding process in plasma electrolytic conditions, using aqueous solutions of 20, 30 and 40 wt% urea. The results showed that all the concentrations evaluated gave lower levels of wear than untreated stainless steel. However, considering the amount of urea used and the environmental emissions from the waste generated, a concentration of 20% by weight of urea in the electrolyte is considered sufficient to increase up to three times the wear resistance of stainless steel. XRD, XPS and microscopy analyses showed that, in the main, the outermost layer of the steel surface treated by electrolytic plasma has a morphology of small craters of chromium and iron oxy-nitrides. A nitrogen diffusion layer was also seen below the oxy-nitrided layer.

Torsional behavior of GFRP-reinforced concrete pontoon decks with and without an edge cutout

Using glass fiber-reinforced polymer (GFRP) bars in precast concrete pontoon decks in aggressive marine environments would eliminate corrosion problems encountered with steel reinforcement. Although wave action usually subjects pontoon decks to torsion, but little is known about the behavior of such structures. Moreover, nothing is known about the effects of cutouts on the torsional behavior of pontoon decks. This study experimentally investigated the torsional behavior of GFRP-reinforced concrete (RC) pontoon decks in terms of the effect of edge cutouts, reinforcement-bar distribution, and rotation direction. The results show that the bar configuration affected the failure behavior and torsional capacity of the GFRP-reinforced concrete decks under torsion. The decks with double-layer reinforcement exhibited slower and narrower cracking growth in the post-cracking stage than the decks with single-layer reinforcement. In addition, the edge cutouts reduced the cracking torque of the solid rectangular decks by an average 17%. The torsional behavior of the GFRP-reinforced planks can be accurately described by the ACI318-14 equation in the cracking stage, while the decks’ post-cracking torsional rigidity can be predicted accurately from the contribution of the GFRP bars.

RETRACTED: The influence of fiber RC beams under flexure on the chloride-induced corrosion

Corrosion of rebars is the main cause of the deterioration of reinforced concrete structures. In an aggressive marine environment, rebar corrosion occurs due to chloride ion penetration of the reinforced concrete (RC). This paper presents the findings of an experimental study conducted to determine the influence of fiber reinforcement on the chloride-induced corrosion and flexural behaviour of reinforced concrete beams. Uncracked and cracked reinforced concrete beams were exposed to a 16.5% chloride solution in a cyclic immersion for three years, causing them to corrode naturally. The half-cell potential test was carried out to monitor the corrosion potentials, and flexural tests were carried out in a three-point bending configuration to assess the structural performance. Gravimetric tests revealed that bars in conventional concrete had higher degrees of corrosion than those in fiber-reinforced concrete with a variation of 11 %. With increasing crack widths (max 0.2–0.3 mm), there was a tendency toward early corrosion initiation, in contrast, fiber addition delayed the process of corrosion initiation by 6 %. Regarding flexural performance, fiber-reinforced beams are significantly better than conventional concrete beams, especially steel fiber incorporated concrete beam's residual flexural strength 16 % more than the conventional concrete beams.

The Feasibility of Using Bipolar Electrochemistry to Study Pitting and Crevice Corrosion of Stainless Steels in Cementitious Materials

The durability of carbon steel reinforced concrete infrastructure is often limited by rate of corrosion damage progression. Over the past couple of decades, corrosion-resistant alloys, such as stainless steels (SS), have garnered attention as a potential way to address the durability of reinforced concrete exposed to aggressive marine environments. However, there are currently no models available to accurately forecast corrosion of stainless-steel reinforced infrastructure and durability projections for carbon steel may not consider the necessary mechanistic steps.Traditional corrosion durability projections adopt the classic two stage model considering the time prior to and following corrosion initiation often distinguished by the point in time where enough chlorides have accumulated at the steel surface to exceed the chloride concentration required to initiate corrosion.[1] Such models do not consider the evolution of pitting or crevice corrosion and the potential for progression to more widespread corrosion. Therefore, research is required to first identify the expected corrosion damage morphology of stainless steels in concrete and then to formulate a theoretical framework that can be used to describe accurately its progression provided expected exposure conditions. This work attempts to develop an efficient yet informative method to study pitting corrosion evolution of steel in concrete with the objective of identifying the role of the cement pore structure on damage evolution and pit or crevice stability.Recently, bipolar electrochemistry has been used to identify potential-kinetic-corrosion damage mode relationships from single measurements on ferritic [2] and duplex stainless steels.[3] Bi-polar electrochemistry (BPE) comprises indirect dc polarization of a conductive element usually immersed in an electrolyte in cases where direct contact to the elements need to be avoided. In application to pitting corrosion studies, BPE followed by post exposure 3D surface metrology can provide pitting characteristics as a function of applied potential from a single experiment. In this work various BPE configurations including single and split electrodes are used to assess the feasible in applying a suitable potential distribution on steel plate specimens that have a thin cement overlay. A finite element model was developed to simulate the applied potential distribution considering the cell geometry and interfacial kinetics. The corrosion damage morphology and the pitting characteristics obtained will be compared to that of chloride-ponded SS reinforced concrete beams to uncover mechanistic insight on SS corrosion damage evolution. Tuutti, K: Corrosion of steel in concrete. 1982, Stockholm. Swedish Cement and Concrete Research Institute, ISSN 0346-6906. Royal Institute of Technology, Stockholm. Department of Building MaterialsZhou, Yiqi, and Dirk Lars Engelberg. "On the application of bipolar electrochemistry to characterise the localised corrosion behaviour of type 420 ferritic stainless steel." Metals10, no. 6 (2020): 794.Zhou, Yiqi, and Dirk Lars Engelberg. "Fast testing of ambient temperature pitting corrosion in type 2205 duplex stainless steel by bipolar electrochemistry experiments." Electrochemistry Communications117 (2020): 106779.

Control and Supervision Requirements for Floating Hybrid Generator Systems.

This work presents a series of devices that generate renewable energy from the marine environment which, in recent years, have aroused increasing interest. In particular, the main types of floating wind generators and marine current turbines are described. Over time, some of these floating generators have evolved in various hybrid modalities, integrating different generation devices into the same system, wind turbines, marine current turbines, wave energy converters, etc., with the objective of multiplying their generation capacity and optimizing the investment made in the floating system. However, this hybridization offers, in some cases, an opportunity to address the problem of controlling the structural stability of the system. Such stability enhancement has been considered a major challenge since the early days of floating wind turbine design. With this objective, in this work, a specific solution is proposed, consisting of a floating hybrid system composed of a wind generation subsystem and a generation subsystem with two marine current turbines. This proposal allows the development of an integrated control system which deals simultaneously with the structural stability of the system and the optimization of the generation capacity. Additionally, other requirements are also highlighted relating to the achievement of economic viability objectives, considering the reliability and availability of the system in the particularly aggressive marine environment, where maintenance operations are especially costly. In this sense, a model of intelligent integration of the tasks of supervision, diagnosis, and predictive maintenance is proposed.

Depth-varying corrosion characteristics and stability bearing capacity of steel pipe piles under aggressive marine environment

The steel pipe pile (SPP) in the offshore steel trestle commonly suffers severe corrosion damage due to the aggressive marine environment. This paper aims at exploring the depth-varying corrosion characteristics of SPPs and their influence on the stability bearing capacity. To do this, the macro-defects along the elevation of corroded SPPs of an actual project were examined through field investigation. The 3D appearances of corroded steel surfaces along the elevation of SPPs were constructed using the optical digital microscope. It was found that SPPs presented varying corrosion damage along the elevation, and the corrosion damage in the splash zone exhibited the largest. In addition, corrosion loss-exposure time models were used considering depth-varying characteristics. The simplified finite element model of the corroded SPP was established and the parameter analysis was conducted. The stability bearing capacity of SPPs without corrosion, with depth-constant and depth-varying corrosion was compared. The results showed that the stability bearing capacity for SPPs serving for five years and ten years decreased by 24.7% and 37.3%, compared with that for SPPs without corrosion; the specification calculation method without considering depth-varying corrosion overestimated the stability bearing capacity of SPPs, significantly when the corrosion duration exceeds five years.

Structural performance deterioration of corroding reinforced concrete columns in marine environments

In aggressive marine environments, rebar corrosion caused by chloride ion ingression in concrete is a critical factor leading to premature failure of in-service reinforced concrete (RC) structures. This paper investigated the structural performance deterioration of marine RC structures affected by rebar corrosion, and proposed new analytical models for predicting the residual bearing capacity of the corroded RC columns. By analyzing the performance deterioration mechanisms of the corroded RC structures, the material degradation models and structural strength reduction models were constructed. Then, the analytical models for estimating the residual bearing capacity of the corroded RC columns under various loading conditions were proposed. From the proposed models, the moment-axial force (M-N) interaction diagrams were plotted for analyzing the influence of corrosion damage locations on the residual bearing capacity. Furthermore, the impact of marine environmental factors on the service life of the corroding RC columns under various loading conditions was investigated. Finally, a numerical example for the corroded RC columns was given to demonstrate the effectiveness of the proposed models. The results showed that the residual bearing capacity of the marine RC columns can be significantly affected by the rebar corrosion level, corrosion damage location, load condition and in-service environment.

Corrosion effect on the flexural behaviour of concrete filled steel tubulars with single and double skins using engineered cementitious composite

Concrete filled double skin tubular (CFDST) members are considered one of the most advanced construction composite forms, consisting of inner and outer tubes with concrete sandwiched between them. This paper presents an experimental study and theoretical analysis of the flexural performance of corroded concrete filled steel tubular (CFST), compared to CFDST beams with engineered cementitious composite (ECC) and normal concrete (NC). ECC is characterised by excellent tensile and flexural behaviour with crack control capacity, which shows great potential for enhancing the flexural behaviour of CFDST, especially in aggressive marine environments. In this study, a 500 µA/cm2 current density was implemented for 170 and 250 h to produce accelerated corrosion with mass losses of 6 % and 9 %, respectively, to investigate the effect of corrosion on the flexural behaviour of regular CFDST and CFDST with different types of infill material. Moreover, due to the shortcomings of normal concrete in preventing both the outward and inward buckling of steel plates, in this study an ECC was incorporated as the infill material between steel tubulars. The experimental results of all samples, including CFST and CFDST, showed that corrosion affects the flexural stiffness, ductility index, and energy absorption more than the ultimate moment strength. In addition, the highest impact of corrosion was for CFST with NC (CFST-NC), whereas the lowest effect was observed in CFDST with ECC (CFDST-ECC). Moreover, there is a lack of consideration regarding the impact of corrosion on the predicted flexural stiffness provided by existing codes. Hence, in this study, a theoretical flexural stiffness analysis was conducted and compared with various codes such as EC4, AIJ, BS5400, and AISC.

Combined Effects of Sulfate and Chloride Attack on Steel Reinforced Mortar under Drying–Immersion Cycles

In this study, X-ray microcomputed tomography (XCT) and nanoindentation techniques were used to evaluate the synergistic action between sulfate and chloride ingress under cyclic drying–immersion conditions on steel-reinforced mortars. Three salt solutions, namely 3% NaCl (Sc), 5% Na2SO4 (Ss), and 5% Na2SO4 + 3% NaCl (Scs), were used and 24 drying–immersion cycles were applied. The results showed that the chloride caused more severe corrosion on steel reinforcement than the sulfate while under the influence of Scs, and the presence of sulfate suppressed the steel corrosion caused by chloride. In terms the damage to the mortar cover, after 24 drying–immersion cycles, the sulfate caused the most severe damage (volume loss of approximately 7.1%) while the chloride resulted in the least damage (volume loss of approximately 2.6%). By comparing Ss and Scs, it was also found that chloride suppressed the sulfate attack by reducing the damage to the mortar cover (volume loss of approximately 6.3% for Scs). Moreover, the degradation of mortar specimens was found to be layer-dependent, as was the distribution of micro-mechanics. Regarding the micro-mechanics, the specimens of the three solutions performed differently in terms of the aforementioned properties, depending on which underlying mechanism was analyzed. This research could allow for a more accurate assessment of the factors influencing building structures in a typical aggressive marine environment.

Dynamic fracture behavior of hygrothermally degraded carbon epoxy composites

Composite structures used in aerospace, automotive, and military applications are often subjected to aggressive marine or water environments during their service life that can cause material degradation over time. Many composites absorb moisture when exposed to wet environments which may affect their microstructure, consequently influencing their bulk material properties and performance. Additionally, certain applications may require them to be subjected to seawater environments where the addition of saline can further degrade the material over time. This experimental investigation examines the effects of moisture absorption and saline on the dynamic fracture behavior of unidirectional carbon epoxy composites. To accelerate mass absorption, samples were soaked in elevated temperature baths (70°C) of either ASTM standard seawater or distilled water. To explore the role of absorption duration on the dynamic fracture behavior, soaking time varied between 3.5 hours and longer than 4 months. Pre-cracked specimens were impacted using a long-bar striker device at 4 m/s, to instigate a dominantly Mode-I (opening) fracture response. Digital image correlation was used in conjunction with ultra-high-speed imaging to track the crack tip surface displacements and an elastodynamic solution for an orthotropic material leveraged to extract the stress intensity factor (SIF) up to and at initiation. The critical SIF of the soaked samples is compared with results from a group of ambient condition, unsoaked samples. Results suggest that moisture absorption causes the matrix to expand and introduce microcracks or delamination between plies as the composite swells to accommodate the additional water, inversely affecting the material resistance to fracture.

Experimental and theoretical investigation of chloride ingress into concrete exposed to real marine environment

Chloride-induced corrosion is a critical issue that influences the durability and mechanical performance of reinforced concrete (RC) structures exposed to marine tidal and splash environments. This paper presents an experimental and theoretical investigation on the chloride transport behavior in concrete exposed to an aggressive marine environment for up to 720 days. Field exposure tests were performed in marine tidal and splash zones, and free chloride concentration profiles for different types of concrete after several exposure times, i.e. 90, 180, 360 and 720 days, were obtained. The effects of the water-to-cement ratio, binder type, exposure environment and exposure time on the time dependency of the chloride diffusion coefficient (D) and surface chloride concentration (Cs) were analyzed and discussed. Based on the obtained results, a modified time-dependent prediction model of chloride ingress into concrete was established and validated by considering the time-dependency effect of material and environmental factors. The results indicate that the comparisons of the predicted chloride profiles using the developed time-dependent prediction model were in good agreement with the results of the real marine exposure test.