Marine Concrete Structures Research Articles

Chloride permeation resistance of sulphoaluminate cement-based composite characterized by both alternating current section and RCM methods

Sulphoaluminate cement (SAC) was widely used for rapid repair and strengthening of building structures due to its excellent quick hardening and high early strength behavior. This study developed a SAC-based engineering cement composites (ECC) with ultra-high molecular weight polyethylene (UHMWPE) and investigated its mechanical properties. Chloride ion permeability coefficient were evaluated by new alternating-current sectioning and rapid chloride migration (RCM). The mechanism of the SAC-ECC against chloride erosion were quantified using nitrogen isothermal adsorption. The results show that the fracture energy, tensile strength and strain of SAC-ECC samples are higher than that of normal ECC. The polyethylene (PE) fiber could significantly improve the flexural strength and toughness with PE fiber content of 0.75 % by volume. The hydration products generated could react with chloride ion to make it chemically stabilized, leading to reduce the chloride ion diffusion coefficient significantly. Based on microscopic analysis (SEM), the pore structure in SAC-ECC composite improved remarkedly while the volume of harmful pore decreased evidently as well. SAC-ECC developed in this paper could be poetically applied to strengthening and repair of marine concrete structures.

Investigating the Synergistic Corrosion Protection Effect of an Alloy Element and Corrosion Inhibitor on Steel Reinforcement Using Machine Learning and Electrochemical Impedance Spectroscopy

Steel reinforcement in marine concrete structures is vulnerable to chloride-induced corrosion, which compromises its structural integrity and durability. This study explores the combined effect of the alloying element Cr and the smart corrosion inhibitor LDH-NO2 on enhancing the corrosion resistance of steel reinforcement. Employing a machine learning approach with a support vector machine (SVM) algorithm, a predictive model was developed to estimate the polarization resistance of steel, considering Cr content, LDH-NO2 dosage, environmental pH, and chloride concentration. The model was rigorously trained and validated, demonstrating high accuracy, with a correlation coefficient exceeding 0.85. The findings reveal that the addition of Cr and application of LDH-NO2 synergistically improve corrosion resistance, with the model providing actionable insights for selecting effective corrosion protection methods in diverse concrete environments.

Chloride transport through the interface in repaired marine concrete systems in a cracked state

AbstractIn repaired marine concrete structures, generally, an interface exists between old and new concrete, however, the influence of this interface on durability has yet not been well understood. In this study 18 reinforced concrete beams with new‐to‐old concrete interfaces (N–O interfaces) were designed to investigate chloride transport through a cracked interface. The effects of crack widths at the interface, concrete strain, and the chloride exposure time were considered, respectively. Results showed that the N–O interfaces having crack widths between 0 and 0.13 mm posed no significant impact on the chloride transport in the depth direction of the N–O interfaces, however when the crack width exceeded 0.13 mm, the chloride concentration gradually increased as the crack width increased. Chloride transport through the horizontal direction of the N–O interface was different between new and old concrete matrix when the crack width reached 0.18–0.20 mm. The surface layer with a range of 5–10 mm depth of concrete was sensitive to the variation of concrete strain, and the evolution of chloride concentration with concrete strain presented a logarithm relationship. Within the exposure period between 60 and 90 days, the increasing rate of chloride concentration was higher than that between 30 and 60 days. The study can provide some recommendations for repair of concrete elements exposed to a chloride‐laden exposure environment.

Mesoscale discrete simulation of flexural behavior of FRP-strengthened RC beams using 3D RBSM

A widely adopted method of strengthening existing reinforced concrete (RC) structures, especially for marine concrete structures, is to use external bonded fiber-reinforced polymer (FRP). However, although numerous studies in this field have been reported, accurate simulation of localized material behaviors such as crack opening and interfacial sliding remains challenging. Compared to other simulation methods, mesoscale models offer the promise of capturing these complexities. Nevertheless, there has been very little application of mesoscale simulations in analysis of FRP-strengthened RC structures due to a lack of relevant constitutive models. To fill this gap, the authors have recently developed local bond models for the FRP-concrete interface in the three-dimensional rigid body spring model (3D RBSM). The model’s parameters are defined with easily interpretable physical implications and straightforward computational methods. In this work, this mesoscale model is extended and applied to simulate the flexural behavior of FRP-strengthened RC beams. The simulation results closely align with experiments in both global and local behaviors. The parametric study conducted in this work highlights the critical role of interfacial normal bond strength between FRP and concrete in dictating flexural behavior. The capability of 3D RBSM in simulating the strain distribution along the FRP and capturing intricate localized behaviors aligned with flexural and shear forces is demonstrated. Overall, this paper reinforces the potential of 3D RBSM as a robust tool for analyzing the complex behaviors of FRP-strengthened concrete structures.

Durability life evaluation of marine infrastructures built by using carbonated recycled coarse aggregate concrete due to the chloride corrosive environment

Due to the harsh marine environment of chloride ion invasion and corrosion, the issues of long-term chloride transport and durability life evaluation for marine infrastructures constructed/maintained by recycled aggregate concrete (RAC) after enhancement remain poorly understood. For our studies, an accelerated carbonation modification method for recycled coarse aggregate (RCA) was adopted to prepare carbonated recycled coarse aggregate (CRCA) samples, and the macroproperties, i.e., apparent density and water absorption, of CRCA were enhanced by approximately 1.40-3.97% and 16.3-21.8%, respectively, compared with those of RCA. An in-door experiment for chloride transport into concrete specimens subjected to a simulated marine environment of alternating drying-wetting cycles was conducted. The chloride profiles and transport characteristics of carbonated recycled coarse aggregate concrete (CRCAC), recycled coarse aggregate concrete (RCAC), and natural coarse aggregate concrete (NCAC) were analysed and compared. The results indicated that the chloride penetration depths and concentrations of CRCAC were approximately 52.6-96.2% of those of RCAC, which highlighted the better chloride resistance of CRCAC. A chloride transport model for marine concrete structures with various coarse aggregate types in a corrosive marine environment was established. Taking a certain harbour wharf as an example, the durability life of this case considering the application of the CRCAC was evaluated based on the chloride transport model, and the durability life of the CRCAC structure was improved by approximately 28.10% compared with that of the RCAC. The CRCAC developed in this paper has improved mechanical performance and durability than those of RCAC, and it has the potential to replace the NCAC and further support the construction and maintenance of marine infrastructures.

Chloride binding mechanism in seawater-mixed UHPC

The rapid development of marine concrete structures and the sharp shortage of freshwater resources contribute to the wide investigation of seawater-mixed ultra-high-performance concrete (SWUHPC). However, few studies have investigated the chloride ions (Cl-) binding mechanism of SWUHPC. Herein, the chloride binding experiments and molecular dynamics (MD) simulation were carried out to reveal the physically and chemically bound Cl- mechanisms of SWUHPC. The results of the experiments clearly demonstrate that the addition of silica fume (SF) led to a significant decrease in the capacity of Cl- binding. Conversely, the incorporation of metakaolin (MK) resulted in a marked increase in the content of chemically bound Cl-. Furthermore, it is revealed through MD simulations that the amount of physically bound Cl- heavily depends on the Ca/Si ratio of C-S-H. A higher Ca/Si ratio results in a stronger electrostatic effect of the C-S-H surface on Cl-, which increases the physical binding of Cl- via Ca-Cl bonds. In addition, it is found that Al[6] and Ca in the interlayer region of C-A-S-H formed the main structure layer (Ca4Al2(OH)122+) of Friedel’s salt, and then chemically adsorbed Cl- in the pore solution. These findings provide novel nanoscale insights regarding the physically and chemically bound Cl- mechanisms of SWUHPC.

A novel LDHs-VB3- inhibitor for rebar corrosion in simulated concrete pore solution: Synthesis, performance and mechanism

Developing novel chloride-trapping inhibitors is of great significance for enhancing the durability of marine concrete structures. In this study, a novel LDHs-VB3- inhibitor was synthesized through the ion exchange method. Then, the corrosion inhibition mechanism of LDHs-VB3- inhibitor for rebar in the whole process of release - capture - adsorption - retardation was studied using experiments and density functional theory (DFT) simulations. The chloride ion exchange test demonstrates that the LDHs-VB3- inhibitor has a chloride trapping capacity of 35.5 mg/g in the saturated Ca(OH)2 solution containing 0.14 M NaCl, implying that it could capture Cl- in concrete pore solution. According to the electrochemical tests, the critical chloride concentration of rebar in the simulated concrete solution containing LDHs-VB3- falls within a range of 0.22 M–0.28 M, which is much higher than that in the solution without LDHs-VB3- (0.10 M–0.14 M). DFT simulations indicate that LDHs-VB3- exhibits more positive binding energy and uneven binding forces in contrast to LDHs-Cl-. Consequently, VB3- could be easily replaced by Cl- and then released into the pore solution of concrete. Moreover, the released VB3- could adsorb on the α-Fe2O3 surface in a concrete environment via the interaction of surface Fe atoms with N and O atoms of VB3-. The preadsorbed VB3- could diminish the interaction of Cl- with the α-Fe2O3 surface by reducing electron transfer, thereby mitigating the risk of passive film breakdown and retarding the chloride-induced corrosion of rebars.

Probabilistic assessment of silane impregnation and electrochemical chloride removal treatment on protection effect against steel corrosion in marine concrete structures

This paper concerns the protective performance of maintenance strategies, i.e. silane impregnation (SI) and electrochemical chloride extraction (ECE), against chloride-induced corrosion for concrete elements in marine environment. The effectiveness of SI treatment is researched through long-term exposure tests, and the efficiency of ECE treatment is considered using a quantitative expression. The failure probability evolution is calculated through reliability theory and Monte-Carlo simulations. The maintenance planning is established, and relevant maintenance costs are determined. The obtained results show that (1) the effective protection life of initially applied silane is longer than 12 years, but the protective performance of reapplied silane is not as pronounced as the silane initially applied; (2) the chloride ions at steel surface are efficiently removed after ECE which is more conducive to sustain the steel rebars free from corrosion; (3) ECE treatment attains the optimal cost and is recommended for long life-span concrete elements in marine environment.

Effect of exposure conditions on the chloride concentration profiles in a marine concrete structure, studied by means of the kernel density estimation technique and a Gaussian–Lorentzian model

The corrosion of the embedded steel due to chloride action is one of the main degradation problems limiting the service life of reinforced concrete structures in a marine environment. Modelling chloride profiles into concrete is a key factor to predict durability of structures. Experimental profiles from the harbour of a Mediterranean city are here studied fitting them to a Gaussian–Lorentzian peak model. This model is suited for the observed peak-shaped profiles, yielding descriptive transport parameters for both the convective and the diffusive zones. The parameters of the diffusive zone are found to be in agreement with the solution of the Fick’s second law of diffusion. The obtained parameters describing the profiles are statistically analysed by means of the kernel density estimation technique in order to determine how exposure conditions affect these parameters. A criterion of probability density distributions overlapping is used to draw conclusions about how exposure time, orientation respect to sea, wind, and splash affect the height and location of the chloride peak concentration, and the transport coefficients in the convective and diffusive zones of the profiles.

Biomineralization To Prevent Microbially Induced Corrosion on Concrete for Sustainable Marine Infrastructure.

Microbially induced corrosion (MIC) on concrete represents a serious issue impairing the lifespan of coastal/marine infrastructure. However, currently developed concrete corrosion protection strategies have limitations in wide applications. Here, a biomineralization method was proposed to form a biomineralized film on concrete surfaces for corrosion inhibition. Laboratory seawater corrosion experiments were conducted under different conditions [e.g., chemical corrosion (CC), MIC, and biomineralization for corrosion inhibition]. A combination of chemical and mechanical property measurements of concrete (e.g., sulfate concentrations, permeability, mass, and strength) and a genotypic-based investigation of formed concrete biofilms was conducted to evaluate the effectiveness of the biomineralization approach on corrosion inhibition. The results show that MIC resulted in much higher corrosion rates than CC. However, the biomineralization treatment effectively inhibited corrosion because the biomineralized film decreased the total and relative abundance of sulfate-reducing bacteria (SRB) and acted as a protective layer to control the diffusion of sulfate and isolate the concrete from the corrosive SRB communities, which helps extend the lifespan of concrete structures. Moreover, this technique had no negative impact on the native marine microbial communities. Our study contributes to the potential application of biomineralization for corrosion inhibition to achieve long-term sustainability for major marine concrete structures.

Preparation and evaluation of TA/APTES-HDTMS hydrophobic nanocomposite coating for enhancing corrosion resistance of concrete

Coating anticorrosive technology has been widely used in marine concrete structures, but there are some problems such as poor adhesion, lack of durability or environmental pollution. Tannic acid (TA) -aminopropyl triethoxysilane (APTES) coating has good adhesion, corrosion resistance and secondary reactivity, and has been widely used in biomedicine etc. fields. However, the feasibility of applying TA-APTES to concrete surface treatment remains to be studied. In this study, hydrophobic nanocomposite coating TA/APTES- hexadecyltrimethoxysilane (HDTMS) was prepared by coupling HDTMS with TA-APTES, and applied to concrete surface treatment. By water contact angle measurement (WCA), Coulomb charge experiment and scanning electron microscopy test, the effects of TA-APTES mixture content, mass ratio of TA to APTES and HDTMS concentration on the hydrophobic property and ionic permeability of coated concrete were investigated. The results indicated that TA/APTES-HDTMS coating prepared with 4.0 mg/mL TA-APTES mixture content, 2:1 mass ratio of TA to APTES and 7.0 % HDTMS solution concentration showed optimal improvement efficiency. In this case, the chloride transport properties and sulfate resistance of coated concrete were studied by chloride and sulfate natural diffusion tests, respectively. The results indicated that compared with uncoated concrete, coated concrete showed better and stable resistance to chloride ion and sulfate. In addition, the chloride transport models of both coated and uncoated concrete were established based on Fick’s Second Law. It was found that the chloride diffusion coefficient of coated concrete was similar to that of uncoated concrete, but the surface chloride content was significantly lower. Meanwhile, the lifetime of TA/APTES-HDTMS coating was evaluated based on the change of surface chloride content and compared with other research literature. Furthermore, by WCA and Coulomb charge experiment, it was concluded that the anti-abrasion property and acid-alkaline resistance of coated concrete were significantly improved. Finally, the cost-benefit analysis of TA/APTES-HDTMS coating and existing commercial coatings also illustrated the advantages of TA/APTES-HDTMS coating.

Durability of mortar and concrete containing pozzolans as a partial cement replacement in the marine environment: a review

This paper reviews the durability of concrete containing pozzolans in marine environments, which mainly focuses on resistance to chloride ion penetration and sulfate attack. The results of previous literature showed that the main ions of seawater are almost similar but the salinity varies with location. The mechanism of chemical reaction between seawater and concrete was carefully reviewed and explained. Besides, the main attacks that caused the degradation of concrete structures in marine conditions were summarized. The results of previous research indicated that using pozzolans (fly ash, slag, metakaolin, rice husk ash, etc.) as a partial cement replacement in concrete improved the durability of concrete such as resistance to chloride ion penetration and resistance to sulfate. The use of pozzolans not only improves the durability of concrete in the marine environment but also solves environmental impacts such as reducing CO2 emissions and landfilling areas. It can be concluded that the utilization of pozzolans in concrete, particularly in marine concrete structures is a promising approach for sustainable development.

Durability of mortar and concrete containing pozzolans as a partial cement replacement in the marine environment: a review

This paper reviews the durability of concrete containing pozzolans in marine environments, which mainly focuses on resistance to chloride ion penetration and sulfate attack. The results of previous literature showed that the main ions of seawater are almost similar but the salinity varies with location. The mechanism of chemical reaction between seawater and concrete was carefully reviewed and explained. Besides, the main attacks that caused the degradation of concrete structures in marine conditions were summarized. The results of previous research indicated that using pozzolans (fly ash, slag, metakaolin, rice husk ash, etc.) as a partial cement replacement in concrete improved the durability of concrete such as resistance to chloride ion penetration and resistance to sulfate. The use of pozzolans not only improves the durability of concrete in the marine environment but also solves environmental impacts such as reducing CO2 emissions and landfilling areas. It can be concluded that the utilization of pozzolans in concrete, particularly in marine concrete structures is a promising approach for sustainable development.

Chloride penetration resistance and chloride binding capacity under different application environments of ferroaluminate cement

Free chloride is a crucial factor that threatens the long-term performance of marine concrete structures. The resistance of cement to chloride penetration and its capacity to bind chloride are important parameters for assessing the ability of cement-based materials to resist chloride invasion. Ferroaluminate cement (FAC) has considerable application potential in concrete used for marine structures; however, its resistance to chloride invasion and mechanism of chloride binding have not yet been revealed. In this study, the chloride diffusion coefficient and chloride binding capacity of FAC, for both internal and external chloride ions, are experimentally investigated and compared with that of ordinary Portland cement (OPC). The results show that the chloride diffusion coefficient of FAC mortar is approximately 2.5 times lower than that of OPC mortar. FAC exhibits finer overall pore distribution and the number of pores with sizes within 10–100 nm is reduced, which is responsible for its notably lower chloride diffusion coefficient. The chloride binding capacity of FAC to internal chloride ions is slightly lower than that of OPC, and a portion of the chloride ions are chemically bound by reacting with ye'elimite during hydration. The chlorides bound by physical adsorption constitute a dominant portion of the entire bound chloride content. In the case of external chloride ions, the bound chloride content of FAC is lower than that of OPC. The chemical chloride binding capacity of FAC is comparable to that of OPC and the lower physical adsorption capacity for chloride in FAC leads to a weaker chloride binding capacity compared to that of OPC.

Investigating the Effects of Recycled Plastic as Fibers on Bending Behavior of Green Concrete Beams Exposed to Marine Environment.

Due to the noticeable production of greenhouse gases in cement production processes around the world, the use of supplementary cementitious materials (SCMs) like metakaolin/zeolite and the production of green concrete is inevitable, which leads to reducing the amount of environmental pollution and, specifically for maritime environments, improving the mechanical qualities of concrete. In addition, nowadays, the increasing use of plastic materials such as disposable glasses is considered a major problem in environmental pollution. Thus, using metakaolin/zeolite as an SCM and disposable glasses as fibers in concrete production may reduce environmental pollution and improve concrete's properties. To do so, in this paper, the flexural behavior of green concrete beams containing metakaolin/zeolite at 10 and 20% as SCMs at 28, 90, and 180 days in the Oman Sea tidal environment was examined by studying the effects of utilizing 0.5 and 1% disposable-glass fibers in ring and strip forms. The findings demonstrate that ring (RFs) and strip fibers (SFs) in green concrete reduce a beam's maximum load capacity (Pmax) by 31%, while RF and SF enhance green concrete beam flexural toughness by 8-20 times. Furthermore, the SF green concrete beams had 24% greater flexural toughness than RF beams at all ages. Finally, by improving the microstructure (by adding SCMs) and flexural behavior of marine concrete structures, in addition to increasing the load capacity and ductility of marine structures, the cracking and penetration of ions decreases; thus, the service life of the structures will increase.

Predictive modelling of surface chloride concentration in marine concrete structures: a comparative analysis of machine learning approaches

Predictive modelling of surface chloride concentration in marine concrete structures: a comparative analysis of machine learning approaches

Research into Preparation and Performance of Fast-Hardening RPC Mixed with Straw.

Based on its characteristics of early strength, good toughness, and excellent mechanical and impact resistance, steel fiber-reinforced fast-hardening reactive powder concrete (RPC) is expected to become an alternative material used in the rapid repair of marine concrete structures. However, the steel fibers have also caused corrosion problems in coastal environments. To make doped fiber fast-hardening RPC more adaptable for use in ocean engineering, this study prepares fast-hardening RPC mixed with straw and studied the effects of straw content and curing age on its slump flow, setting time, and mechanical performance (flexural strength, compressive strength, and flexural toughness). The effects of straw addition on the compactness and hydration products of fast-hardening RPC were studied through macro- (ultrasonic analysis) and micro-scopic analysis (electron microscopy scanning and X-ray diffraction patterns). The straw content mentioned in this paper refers to the percentage of straw in relation to RPC volume. The results showed that straw reduced the fluidity of RPC slurry by 10.5-11.5% compared to concrete without straw, and it accelerated the initial setting of RPC slurry. When the straw content accounted for 1% of RPC volume, the setting rate was the fastest, with a increasing rate being 6-18%. Compared to concrete without straw, the flexural and compressive strength of fast-hardening RPC was enhanced by 3.7-30.5%. When the content was either 3% or 4%, the mechanical properties improved. Moreover, when the straw content accounted for 4% of RPC volume, the flexural toughness was the highest, with the increase rate being 21.4% compared to concrete without straw. Straw reduces the compactness of fast-hardening RPC.

Time variation law of chlorine diffusion coefficient of marine concrete structures in tidal zone and its influence on service life

Chloride diffusion coefficient (Da) is an important parameter to predict chloride ion concentration in concrete, which is of great significance to the study of durability and service life of concrete structures in the Marine environment. The alternating wet and dry environment in tidal zone has a significant impact on the deterioration of concrete's chloride ion erosion resistance. It is extremely important to study the chloride ion diffusion coefficient in the tidal zone. In this paper, the apparent chloride diffusion coefficient (Da) and its time-dependent constant (m) of concrete were calculated on the basis of a large number of natural exposure test data and engineering data in tidal zone at home and abroad, the time-varying law of chloride diffusion coefficient of marine concrete structures in tidal zone were discussed. The ChaDuraLife Model, DuraCrete model and Life-365 model were utilized to calculate the service life of concrete structures based on the immersed tube tunnel in the north Marine environment of China. The results showed that Da in tidal zone decreases with exposure time and presents a power function relationship. It was found that proper addition of mineral admixtures could improve the chloride ion erosion resistance of concrete structures in tidal zone during long-term service by reducing the chloride ion diffusion coefficient. The type of mineral admixture and the value of m would affect the calculation result of the service life of concrete structures. The addition of mineral admixture would lead to the increase of m, thus prolonging the service life of concrete structures. Service life calculated by different models was changed. The value of m of DuraCrete model was larger, so the calculated service life was longer. Similarly, the calculated service life of Life-365 model was shorter. It was noted that the ChaDuraLife Model was the most economical and safe model to predict the service life of concrete structures.

Service life prediction model for marine concrete structures considering structural shape and time-dependent behaviour

A new service life prediction model for marine concrete structures considering the structural shape and time-dependent behaviour of model parameters was proposed in this study. First, a lumped concentration matrix for both triangular elements of two-dimensional diffusion and linear elements of one-dimensional diffusion was developed based on the Galerkin's method of weighted residual and approximate interpolation function, respectively. Then, a dual time-dependent numerical model for chloride diffusion in marine concrete structures was established by considering the time-dependent behaviour of both chloride diffusion coefficient (D) and surface chloride concentration (Cs). Meanwhile, a new service life prediction model for marine concrete structures that considers the influences of structural shape and time-dependent behaviour of model parameters was proposed. Finally, the influences of the structural shape and the time-dependency of D and Cs on service life were investigated. Analysis results show that the service life would be underestimated if the time-dependent behaviour of D or Cs were ignored, while the service life would be overestimated when the influence of structural shape was neglected. Compared with Cs, the time-dependent behaviour of D has more significant effects on service life of marine concrete structures.

Mechanical characterization of recycled-PET fiber reinforced mortar composites treated with nano-SiO2 and mixed with seawater

The study investigated the use of polyethylene terephthalate (rPET) fibers for strengthening construction materials. The addition of 0.5 vol% rPET fibers to mortar was studied, but the smooth surface of rPET resulted in weak bonds with the mortar matrix, leading to a decreased interfacial transfer zone (ITZ) compared to the surrounding matrix. To address this issue, nano-particle and NaOH hydrolysis were used to improve the ITZ bond strength and frictional behavior. Additionally, surface treatment of rPET using NaOH and silane coating was performed to enhance the hydrophilicity and bond strength with the matrix. The effects of seawater on the material were also studied using XRD. Additionally, cemGEMS analysis was also conducted. The SEM was used to observe the degree of bonding at the ITZ between rPET and the mortar matrix. The study showed that adding 0.5 vol% of rPET fibers had a significant impact on the tensile strength and fracture energy of mortar, and the fiber dispersibility was a crucial factor in controlling its mechanical properties. The low-cost recycled PET fibers were also found to be effective as a reinforcing agent in seawater-mixed mortar for marine applications, increasing the mortar's fracture energy by 188–802%. Therefore, these fibers can be used in coastal structures requiring impact-resistant non-metallic materials, such as wave-dissipating concrete blocks or marine concrete structures reinforced with non-corrosive materials like FRP.