Concrete Structures In Marine Environment Research Articles

Comparative analysis of microdamage-affected chloride transport in concrete under static and dynamic hydraulic pressure

Concrete structures in marine environments frequently encounter the adverse impacts of hydraulic pressure, leading to a decrease in their durability. This study aims to conduct a comparative analysis of the internal microdamage in concrete when subjected to static and dynamic hydraulic pressure of equal intensity, and to examine the influence of such damage on chloride transport. By employing potentiometric titration, MIP, N2 adsorption, and AFM tests, the chloride concentration, pore structure parameters, and microscale elastic modulus of concrete under static and dynamic hydraulic pressure were analyzed. The results indicate that dynamic hydraulic pressure accelerates chloride transport in concrete. Compared with static hydraulic pressure, dynamic hydraulic pressure — sustained at the same intensity—results in an elevated threshold pore size along with an increased most probable pore size of the concrete. Furthermore, dynamic hydraulic pressure induces the expansion of microcracks, consequently decreasing the microscale elastic modulus of concrete. The use of mineral admixtures can effectively mitigate the damage evolution of concrete microstructure subjected to dynamic hydraulic pressure. Besides, a model is developed for relative chloride diffusion based on the principle of energy conservation and from the evolution law of the microscale elastic modulus gleaned from AFM tests. Through calculations, it can be found that the crack propagation rate and the decline rate of the relative chloride diffusion coefficient Df1Df2 increase markedly when dynamic hydraulic pressure intensity surpasses 40,000 Pa. The propagation of the crack length is moderated by a larger initial crack width.

A hybrid method for bond-slip behavior of reinforcement rebar in steel-polypropylene hybrid fiber reinforced concrete structures in marine environments

Fiber-reinforced concrete is an advanced class of construction materials that display higher mechanical and durability performance, but limited information is available on the bond behavior of reinforcement rebar in steel-polypropylene hybrid fiber reinforced concrete (SPHFRC) in marine environments, which produce crack states commonly seen in reinforced concrete structural components. In this study, a hybrid method for predicting the bond response behavior of SPHFRC under monotonic and cyclic loading was developed. The proposed method combining mechanical-driven model and generative adversarial networks (e.g., GAN) method. Experimental databases were constructed. Two empirical models were developed. The GAN method enhanced its prediction accuracy through adversarial training support by database and hyper-parametric analytics. Finally, to verify the accuracy and effectiveness of the developed model, a total of 65 SPHFRC specimens under cyclic loading were conducted. The comparison shows that this model can reproduce the corrosion-induced bond deterioration of SPHFRC. The model can also capture the cyclic bond degradation of SPHFRC and other types of ultra-high-performance concrete with an acceptable range.

An experimental investigation on mitigating cracks and augmenting the endurance of concrete structures in marine environment by bio-mortar immobilised with halophilic bacteria

In coastal areas, built structures encounter hostile conditions and forces that can cause them to deteriorate over time owing to saltwater exposure, tidal forces, reinforcement corrosion, and freeze–thaw cycles. Early age cracks in such structures accelerate the rate of deterioration, and the current research focuses on alleviating such threats. This paper evaluates the performance of a self-healing mortar made by encapsulating expanded perlite with the bacterium Halobacillus Halophilus MCC2188. Mortar cube specimens of size 70.6 mm × 70.6 mm× 70.6 mm were prepared with cement: fine aggregate in 1:3 ratios. A 10% volume of the fine aggregate fraction was substituted with the expanded perlite immobilised with bacterial spores and nutrients. The expanded perlite aggregates were coated with sodium silicate and cement solution to protect the spores from the nonconducive environment. The specimens were subjected to fully and partially submerged marine water curing. The mechanical properties and self-healing potential were evaluated, and the precipitated polymorphs in completely healed cracks were identified and examined by characterisation techniques such as XRD, FEGSEM, FTIR, and TGA-DTG. The marine bacterium under investigation can tolerate the high salt concentrations commonly found in seawater and saline marshy soil and produce calcite through the metabolism of organic compounds, making it a suitable microorganism for self-healing applications. Crack widths of up to 0.84 mm and 92.79% average strength recovery were achieved in 56 days post-cracking, and the pace of healing was quicker in partially submerged curing conditions. The results showed improved self-healing, strength regain and mechanical strength and proved to be an efficient tool for enhancing the endurance of biomortar in severe marine exposure conditions.

Measurement plan targeting the accuracy of calibrated chloride ingress model for concrete structures in marine environment

Surface chloride concentration (CS) and chloride diffusion coefficient (DCl) are key parameters for durability assessment of concrete structures in marine environment; they are time-varying and highly dependent on the exposure condition. To reasonably model their behaviors at a specific location, durability measurement data are often needed to calibrate the apparent chloride ingress model based on Fick’s second law. In view of the significant variability of measurements and the bias of chloride ingress model, it remains unaddressed how to formulate a measurement plan to make the calibrated model achieve the required accuracy. This paper first establishes the probabilistic time-dependent models of CS and DCl with both sample variance and model bias considered, and then introduces the Bayesian method to update the two models using measurement data. By assuming realistic models of CS and DCl and comparing them with updated ones, the effectiveness of Bayesian updating method is demonstrated, and the key factors affecting the updated model accuracy are discussed, including prior estimate of parameters, model bias and measuring times. On this basis, a determination method of measurement plan targeting the calibrated model accuracy is proposed, which works for both Bayesian updating and linear fitting for model calibration. And finally numerical examples are presented to show the validity of the proposed method. The sample size obtained by the proposed method is exact for linear fitting and slightly more than required for Bayesian updating.

Moisture transports in high-cycle compressive fatigue-damaged concrete

Concrete structures in marine environments, e.g. bridges, usually undergo fatigue loads induced by vehicle transportations. Fatigue loads may lead to growth of micro-cracks in concrete which would initiate the additional transport channels and thus accelerate the penetration of moisture and some other aggressive agents into concrete This paper presents an investigation on the moisture transports in fatigue-damaged concrete. Axial compressive fatigue tests were conducted to obtain concrete with uniform compressive fatigue damage and residual strains were used as indexes to estimate the fatigue damage degrees of concrete. Water absorption and air drying tests were subsequently designed and carried out on fatigue-damaged concrete. Test results showed that the absorption rate increased with the residual strain and moisture could evaporate out of the exposed surface more easily of fatigue-damaged concrete than non-damaged concrete, which indicated that degradation of impermeability performance of fatigue-damaged concrete. In addition, prediction model of moisture transport in fatigue-damaged concrete was developed based on assumption of fictitious crushing band, and the accuracy of model was verified based on experimental results. The moisture transports in gradient fatigue-damaged concrete were further investigated based on the validated model with two damage indexes, i.e. residual strain at the exposed edge and residual curvature. The numerical results showed that the moisture transport rates are slightly decrease by the increase of residual curvature as the residual strain at the exposed edge was fixed. As compared to residual curvature, the rates of moisture transport in gradient fatigue-damaged concrete were more sensitive to the residual strains at the exposed edges.

Experimental Investigation and Numerical Model for Chloride Diffusivity of Long-Age Fly Ash Cement Slurry

Fly ash is a by-product of coal-fired thermal power plants and offers great potential for the use of resources. To effectively improve the durability of reinforced concrete structures in marine environment and achieve waste to treasure, fly ash is widely used as a pozzolanic material due to its long-hydration characteristics and effects of micro-aggregate, micro-filling and secondary hydration. In this study, both the experimental investigation and numerical simulation are carried out to study the chloride transport characteristics of fly ash cement paste. The variation in chloride diffusivity with fly ash content, water-to-binder ratio and curing age up to 360 days is studied via accelerated conductivity measurement, and it is found that the above three experimental variables have a significant impact on the chloride diffusivity. For the influence of the dosage of fly ash, the optimum dosage is 30%. By introducing specific rules for the particle distribution, the fresh fly ash cement paste is first made. Based on the volume change characteristics of fly ash and cement particles after hydration, the vector hydration model of fly ash cement paste is established by considering the water shortage effect caused by hydration layer interference. After the accuracy of this hydration model is verified by the results from third-party experiments, the random walk algorithm is proposed to calculate the diffusion coefficient of the reconstructed mineral admixture cement paste. By comprehensive comparison with the experimental results from the third-party and self-conducted experiments, the numerical model for predicting the chloride diffusivity of fly ash cement paste is verified.

Experimental based time-dependent reliability assessment of corrosion initiation for PC girders in frozen marine environment

Chloride induced corrosion is the main reason for the deterioration of concrete structures in marine environments, and the prediction of corrosion initiation life is one of the greatest challenges for preventative maintenance. To conduct a corrosion initiation assessment of PC girders in frozen marine environment and support preventative maintenance, a time-dependent reliability assessment method is developed. Long-term exposure experiments and in-house tests are combined to calibrate the chloride diffusion model, and then a probabilistic diffusion model is proposed based on the randomness of the key model parameters. Through the analysis of the target reliability index of corrosion initiation, the risk-function based time-dependent reliability assessment method is developed. Finally, a case study is introduced to illustrate the application of the proposed method. It is found that the surface chloride concentration on concrete structures in frozen marine environments increases at the beginning of service life and it tends to be stabilize when the service time is around 9–10 years. The age reduction factor of chloride diffusion can be described as the linear function of cementitious composition. The target reliability indices of corrosion initiation are suggested as 2.46, 1.50 and 1.13 for the referenced periods of 1, 10 and 20 years. The corrosion initiation life is very sensitive to the tensile stress level of concrete, and it decreases linearly with the increasement in tensile stress when the stress is not higher than 2 MPa.

Electrical resistivity tomography results analyzed with two inversion methods to determine chloride profiles on BFS concrete having very high electrical resistivity

Non-destructive evaluation techniques are increasingly used for the investigation of reinforced concrete structures in marine environment. In this paper, the possibility of evaluating chloride profiles by Electrical Resistivity Tomography (ERT) on Blast furnace slag (BFS) concrete at a long curing period so having high electrical resistivity was studied. This was carried out by monitoring the chloride profile for two 6-years old concretes (with and without slag) during a diffusion campaign using a Non-Destructive Evaluation (NDE) methodology. The methodology is based on determining the electrical resistivity profiles by carrying out surface apparent resistivity measurements submitted to two different inversion processes. The resistivity profiles are then converted to chlorides profiles using calibration curves. The chlorides profiles were also compared by those assessed by Destructive Evaluation (DE) at three different exposure periods, which displays a high similarity between DE and NDE profiles.

Biogalvanic cathodic protection of reinforced concrete structures in marine environments

Cathodic protection is an efficient solution that is implemented on reinforced concrete structures to address corrosion issues and prevent further deterioration. However, it has significant drawbacks in terms of sustainability. This paper explores a new biological CP technology for reinforced concrete structures in marine environments, where a bioanode is buried in marine sediments, and electrons are supplied through the oxidation of various substrates by electro-active micro-organisms. The issue was addressed both numerically and experimentally, with a first-of-a-kind experimental verification on a laboratory specimen. This new solution offers three fundamental advantages: autonomous operation, green solution, and free current supply.

Corrosion of Reinforced A630-420H Steel in Direct Contact with NaCl Solution.

The deterioration of reinforced concrete structures in marine environments presents multiple problems due to the premature degradation of reinforced steel. This work aimed to study the corrosion of reinforced A630-420H steel when exposed to a 0.5 M NaCl solution. Although this carbon steel is the most widely used material for reinforced concrete structures in Chile, there is limited research on its resistance to corrosion when in contact with saline solutions. The electrochemical reactions and their roles in the corrosion rate were studied using linear sweep voltammetry, weight loss, scanning electron microscopy, and X-ray diffraction techniques. This analysis is unique as it used the superposition model based on mixed potential theory to determine the electrochemical and corrosion parameters. The outcomes of this study show that A630-420H steel has a higher corrosion rate than those of the other commercial carbon steels studied. This fact can be attributed to the competition between the cathodic oxygen reduction reaction and hydrogen evolution reaction, which also depends on the environmental conditions, exposure time, stabilization of the corrosion products layer, and presence of chloride ions. Additionally, the results under mechanical stress conditions show a brittle fracture of the corrosion product oriented longitudinally in the direction of the bend section, where the presence of pores and cracks were also observed. The corrosion products after corrosion were mainly composed of magnetite and lepidocrocite oxide phases, which is in concordance with the electrochemical results.

Numerical modeling of chloride diffusion in cement-based materials considering calcium leaching and external sulfate attack

Chloride-induced corrosion of steel bars can shorten the service life of concrete structures in marine environment. Therefore, a numerical model that can accurately characterize the chloride diffusion in marine concrete can help to evaluate the service durability of structures. In this paper, a novel chloride diffusion model considering the coupling effect of calcium leaching and sulfate attack in cement-based materials is proposed. The model can not only simulate the increase of porosity structure and the desorption of bound chloride caused by calcium leaching, but also characterize the competitive antagonism between sulfate and chloride salts in cement-based matrix, which produces expansive products to fill pores and promotes the desorption of bound chloride. The proposed model was further developed in COMSOL, and verified by two groups of literature experimental data. Then, the verified model was applied to investigate the coupling effect of calcium leaching and external sulfate attack on chloride diffusion process in cement-based materials. The results show that the proposed model can effectively reproduce the chloride diffusion process in both groups of tests well. In contrast to the single influencing factor, the coupling effect of calcium leaching-sulfate attack on the chloride diffusion process in cement-based materials shows that there is a phenomenon of inhibiting chloride diffusion in the early stage of erosion, but it shows a promoting effect in the later stage. Compared with sulfate attack, calcium leaching always dominates the influence of chloride diffusion in cement-based matrix. Furthermore, considering the coupled effect of leaching-sulfate attack, the initial corrosion time of reinforced concrete is about 24.5% earlier than that without considering the coupling effect. Increasing the thickness of steel bar cover layer and reducing the initial porosity of matrix can effectively delay the occurrence of steel bar corrosion in cement-based matrix.

An improved method for predicting the shear strength of corroded reinforced concrete beams with experimental and numerical validation

Shear failure of reinforced concrete (RC) beams is a brittle failure without giving sufficient warning. Steel bar corrosion is one of the main deterioration phenomena for concrete structures in marine environments. However, the effect of steel bar corrosion on the shear-transfer mechanism of RC beams is not yet fully understood, and existing findings are insufficient for reasoned and accurate prediction of shear strength. Thus, the primary objective of this study was to propose and validate a revised fictitious-support-point method for better predicting the shear strength of corroded RC beams. The revised method determines the fictitious support points based on a more transparent mechanical model than previously. Finite element simulation confirms the validity of the revised method from the load-bearing mechanism point of perspective. Validation with copious previously-published test data show that the revised method predicts the shear strength of corroded RC beams more accurately and reasonably than the existing method proposed by other researchers. This study contributes to effective and reasonable maintenance of corroded RC structures.

Fundamental Design Concepts of a Modular Pier System Using Ultra-High-Performance Concrete for Solving Construction Errors

Concrete structures in marine environments are prone to deterioration and damage due to chloride ion penetration, freezing and thawing, and chemical erosion. Ultra-high-performance concrete (UHPC) mixed with steel fibers has been proposed as a solution to enhance the durability and mechanical properties of concrete in marine environments. Although several studies have been conducted in this regard, they have yet to focus on addressing errors that may be caused during the construction of offshore piers. Therefore, this study proposes a modular system to control horizontal and vertical errors during construction using a new connecting core type. UHPC with a fiber content of 0.75% was considered the optimum mix proportion because this met the tensile and compressive strength requirements and the chloride attack resistibility requirements of marine structures. The structural performance of a specimen constructed using modular technology was evaluated. The results of the lateral load resistance experiments showed minimal deformation in the girder and pier. Additionally, both the precast and cast-in-place types met the criterion of load resistance. This study contributes to the advancement of construction technology in marine environments by considering both material performance and construction conditions.

Empirical Study of Surface Deterioration Analysis Based on Random Fields for Reinforced Concrete Structures in Marine Environment.

Corrosion-induced deterioration of the in-service marine reinforced concrete (RC) structures may result in unsatisfactory serviceability or insufficient safety. Surface deterioration analysis based on random fields can provide information regarding the future development of the surface damage of the in-service RC members, but its accuracy needs to be verified in order to broaden its applications in durability assessment. This paper performs an empirical study to verify the accuracy of the surface deterioration analysis based on random fields. The batch-casting effect is considered to establish the "step-shaped" random fields for stochastic parameters in order to better coordinate their actual spatial distributions. Inspection data from a 23-year-old high-pile wharf is obtained and analyzed in this study. The simulation results of the RC panel members' surface deterioration are compared with the in-situ inspection results with respect to the steel cross-section loss, cracking proportion, maximum crack width, and surface damage grades. It shows that the simulation results coordinate well with the inspection results. On this basis, four maintenance options are established and compared in terms of the total amounts of RC panel members needing restoration and the total economic costs. It provides a comparative tool to aid the owners in selecting the optimal maintenance action given the inspection results, to minimize the lifecycle cost and guarantee the sufficient serviceability and safety of the structures.

Non-uniform Corrosion Mechanism and residual life forecast of marine engineering concrete reinforcement

Reinforced concrete structures are commonly employed in civil engineering due to their low cost and high performance. However, their exposure to the marine environment, which is typically characterized by elevated salt content and humidity levels, heightens the probability of corrosion. Such corrosion can lead to a decrease in the service life of these structures, which is of utmost importance to predict in order to prevent potential safety hazards. To address this issue, this study investigated the corrosion mechanism of reinforced concrete structures in the marine environment and found Cl- concentration to be the most critical parameter for the corrosion of steel. Afterward, a predictive model is proposed based on the Back Propagation Artificial Neural Network (BPANN) to estimate the residual service life of reinforced concrete structures in different marine environments by forecasting the Cl- concentration in reinforced concrete components. The results demonstrate the high accuracy of the proposed BPANN model, with a maximum relative error of 6.292 %. Consequently, the residual service life forecast system of reinforced concrete structures proposed in this study can provide useful guidance based on the simplistic framework for designing concrete structures in the marine environment by predicting their effective service life. Thus, this study provides valuable insights for promoting the safety and economic benefits of reinforced concrete structures in the marine environment.

A systematic conditional assessment of strength and durability damage of concrete structures in marine environments

The marine environments reduce the working life of the concrete structures owing to the severe exposure to the chemical ingress, and continuous contact with the humid air, and saline soil conditions. A scientific investigation and the conditional assessment of the existing structures may be helpful to learn the damage mechanism. This article represents the scientific conditional assessment of some existing old concrete structures in the coastal areas of Jamnagar and Dwarka of Gujarat. The objective of the study was to collect information on the types and severity of the damagesin the existing structures and preparing an assessment rubric mentioning the significance of modes of marine environment resulting in a specific damage type. To evaluate the severity of the damages, the parametric approach and a root cause analysis including the experimental investigations on the collected samples has been utilized. The outcomes revealed several interesting observations those have been classified into three major attributes namely material limitations, structural design and third as the gross environmental impacts. The study encouraged the authors to dig deeper in the area of work and showed potential of the methodology to understand the damages caused by the marine environments to the on-shore concrete structures.

A non-linear multiscale chemo-mechanical model describing the delayed evolution of concrete structures in marine environments

The failure of offshore structures is a major issue as they lead to economic, environmental, and social disasters. Assessing the durability and long-term behavior of these structures subjected to chemical and mechanical degradation is subsequently critical. The analysis of these coupled phenomena induced by seawater attack and mechanical loading is complex and requires the development of innovative measurement systems and modelling strategies. Thus, multiscale protocols, starting from the microscopic scale of the cement paste, seems relevant for the characterization of the chemo-mechanical behavior of offshore structures. Therefore, the competition between protective layers' formations and harmful effects of seawater ions has been coupled with the creep phenomenon.

Solution Uptake in Cylindrical Carbon-Fibre-Reinforced Polymer (CFRP) Tendons

Salt water exposure conditions relevant to carbon-fibre-reinforced polymer (CFRP) prestressed concrete structures in marine environments are investigated. The diffusion into relatively small diameter CFRP tendons can be a lengthy process so the prediction of the long-term moisture uptake using short-term experiments on thin films of epoxy would be advantageous. However, the fibre inclusions within a composite introduce complexities, and factors are typically required for correlation with pure epoxy specimens. Diffusion parameters based on moisture uptake result from CFRP tendons exposed to salt water solution at 20°C and 60°C are compared with those obtained using equivalent thin film specimens. The higher temperature is selected to accelerate the moisture uptake. It is found that the measured ratios of tendon and epoxy diffusivity were temperature dependent, and the combination of the higher temperature and salt solution leads to an increased propensity for moisture uptake in the tendon. Existing analytical models to predict the CFRP tendon diffusivity from that of a thin film of epoxy did not appear to capture the observed trends. However, predictions using a unit cell with a fibre interface zone suggest that this may be due to an increased diffusivity in the interphase region.

Durability of FRP bars and FRP bar reinforced seawater sea sand concrete structures in marine environments

• Combination of the alkaline and marine environments aggravates the degradation of mechanical properties of FRP bars. • The variability of mechanical properties of FRP bars shows an increasing trend. • Bearing capacities of FRP bar reinforced SSC components decrease and the failure mode changes. • Environmental reduction factors in current codes are conservative. Fiber reinforced polymer (FRP) is one of the alternatives to steel, and can be directly used in seawater sea sand concrete (SSC). But FRP material still has durability problems in corrosive environments, which is one of the hot and difficult issues of current research. Based on the existing literature, this paper combs the degradation of the long-term property of FRP bars and the durability of FRP bar reinforced SSC (FRP-SSC) structures in the marine environment. The combination of the alkaline environment of concrete and the salt ions in sea sand and seawater aggravates the dissolution of the resin and debonding of the fiber-resin interface of FRP bars (particularly for BFRP bars). Therefore, the mechanical properties of FRP bars degrade with high variability which leads to the reduction of bonding between SSC and FRP bars. Additionally, the bearing capacity of FRP bar/steel-FRP composite bar (SFCB) reinforced SSC components in marine environments decreases, and the failure mode of components changes. The current codes use environmental reduction factors in the durability design of FRP bar reinforced concrete structures. But the values of reduction factors are conservative. Finally, it is pointed out that the quantification of variability for the mechanical property of FRP bars after long-term service, and the time-dependent reliability-based design methods of components are needed for further studies.

Service Life Design for Concrete Engineering in Marine Environments of Northern China Based on a Modified Theoretical Model of Chloride Diffusion and Large Datasets of Ocean Parameters

In this study, through experimental research and an investigation on large datasets of the durability parameters in ocean engineering, the values, ranges, and types of distribution of the durability parameters employed for the durability design in ocean engineering in northern China were confirmed. Based on a modified theoretical model of chloride diffusion and the reliability theory, the service lives of concrete structures exposed to the splash, tidal, and underwater zones were calculated. Mixed concrete proportions meeting the requirement of a service life of 100 or 120 years were designed, and a cover thickness requirement was proposed. In addition, the effects of the different time-varying relationships of the boundary condition ( C s ) and diffusion coefficient ( D f ) on the service life were compared; the results showed that the time-varying relationships used in this study (i.e., C s continuously increased and then remained stable, and D f continuously decreased and then remained stable) were beneficial for the durability design of concrete structures in marine environment.