Concrete Structures In Marine Environment Research Articles

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.

A predictive model for determining shear strength and shear fracture energy of FRP bars in alkali-activated slag seawater coral aggregate concrete

Bond parameters between alkali-activated slag seawater coral aggregate concrete (ASSCAC) and fiber reinforced polymer (FRP) bars are necessary to be determined rationally for future service of the new concrete structures in marine environment. The intention of this paper is to develop a predictive model for determining the realistic local shear strength and shear fracture energy incorporating the heterogeneity and discontinuity in the interface region. First, central pull-out tests were performed to study the bond properties between FRP bars and ASSCAC. Ordinary Portland cement CAC (OPCAC) was prepared for comparison. It is found that the ribs on the bar surfaces were seriously abrased and the extent of damage was more serious in the ASSCAC. Subsequently, a microstructure characteristic parameter was introduced indicating the heterogeneity of the interface region and determined as the rib spacing on the bar surface according to the analysis of failure process. The shear crack propagation was discretized by a discrete number. The local shear strength and shear fracture energy were then linked to the maximum pull-out load via the microstructure characteristic parameter and discrete number. Once the maximum load was given from the test, the two bond parameters were conveniently predicted from each specimen. The results indicated that the predicted local shear strength was apparently higher than the maximum average bond stress which was usually used to represent the local shear strength in traditional methods. As the bond length-to-microstructure characteristic parameter ratio increased, the predicted local shear strength showed a certain reduction but the predicted local shear fracture energy was significantly enhanced because of the reduced boundary effect. Moreover, the predicted bond parameters of the FRP bars in the ASSCAC were generally larger than those in the OPCAC.

Seawater resistance mechanism of reinforcing bar–concrete composite structures restored by repair material incorporating multiple admixtures in a simulated marine splash zone

To improve the durability of concrete structures in marine environment, a marine cementitious repair material (MCRM) incorporating silica fume (SF), water-reducing admixtures (WRA), ground granulated blast furnace slag (GBFS), and desulfurized gypsum (DG) was prepared and its properties were investigated, and the seawater resistance mechanism of reinforcing bar–concrete composite structures restored by the MCRM was revealed in the simulated marine splash zone. The results show that incorporation of the SF-WRA-GBFS-DG composite materials increased the compressive strength, decreased the free chloride diffusion coefficient, enhanced the bond strength of the mortars, and improved the seawater resistance of the restored composite structures. The increase in mechanical properties and the decrease in chloride permeabilities were attributed to the combined effect of the SF-WRA-GBFS-DG composite materials, which increased hydration products such as C–S–H gel and refined the pore structure of the samples. Further, it also reduced the drying shrinkage of the mortars, which was attributed to an increase in the ettringite content, and consumed calcium hydroxide to form additional C–S–H gel, thereby decreasing the quantity of crystals at the adhesive interface. These results have important engineering significance in the safety of deteriorated reinforcing bar–concrete composite structures used in a marine environment.

Evaluation of the Prediction and Durability on the Chloride Penetration in Cementitious Materials with Blast Furnace Slag as Cement Addition

Blast furnace slag (BFS) is a mortar additive in which the utilization of varied curing conditions and the basicity of BFS determine the fineness of the resulting mortar and, thereby, its salt prevention properties. This study evaluates and compares the salt-prevention properties of mortar prepared by either steam curing or water curing. The physical properties, for example, the BFS fineness, revealed the factors significantly affected by basicity that influence the salt-preventive properties of mortar in the specimens examined, such as the lead time and diffusion coefficient. Furthermore, these factors were also significantly affected by differences in curing conditions and other physical properties. However, few studies have examined its use in reducing chloride ion permeability as the main factor of corrosion reactions. Thus, this study evaluates specific surface, water/binder ratio (W/B), and curing conditions on the chloride penetration in cementitious materials with blast furnace slag as cement addition in terms of delaying chloride ion penetration, which affects corrosion reactions. Results of the study are intended to guide development of products for use in the precast concrete industry, toward extending the life of concrete structures, especially reinforced concrete structures in marine environments. In addition, the resulting durability measurements from the experiment conducted are illustrated. This study indicates that differences in Blaine size properties significantly influence water curing. Furthermore, results reveal the effects of combining BFS with various Blaine values and ratio-affecting properties on mortar. In conclusion, concrete materials that decrease durability against chloride attack and improve mechanical properties for precast manufacturer industrial applications are successfully developed in this study. In addition, the use of water-curing conditions, high Blaine value, high cement replacement ratio, and W/B tend to improve the general mechanical property performance and durability against chloride ion attack.

3D meso-scale simulation of chloride ion transportation in cracked concrete considering aggregate morphology

Many experimental and numerical studies have been conducted to explain chloride ion penetration in concrete including aggregates, ITZ and mortar. To my best knowledge, there are few devotion on the relationship between three-dimensional real cracks and chloride ion transportation. Based on spherical harmonic theory, reconstruct the particle generated from smoothing Voronoi polyhedron cell by Loop subdivision to simulate the morphology of real aggregate, and this process performs relatively good efficiency in generating sets of concrete model with different features (mainly aggregate volume fraction, fractal dimension). Consequently, a novel method of representing crack characteristics based on spherical harmonic theory is proposed for analysis, construct a bridge between aggregate morphology and crack characteristics. In view of chloride penetration depth, crack changes the profiles significantly, which accounts for the phenomenon that the existence of crack makes statistical results of chloride concentration on different cross-sections of models fit well with bimodal Gaussian distribution. Volume fraction and morphology of aggregates are mainly correlated to decline rate of gap between chloride concentration of region near crack and the remaining. Both are meaningful for further predict the time to corrosion initiation in reinforced concrete structures in marine environment.

Analysis of time-dependent chloride diffusion in surface-treated concrete based on a rapid numerical approach

Reinforcement corrosion induced by chloride penetration is a major threat to reinforced concrete structures in marine environments. The use of surface treatments to improve the durability of reinforced concrete structures has drawn increasing attention in recent decades due to their cost-effectiveness and convenience in construction. However, current knowledge of a practical, durable design to protect surface-treated concrete structures from chloride-induced steel corrosion remains insufficient. On this account, a rapid numerical approach was developed in this study to analyse the chloride diffusion in bilayer materials. In this approach, the time-dependency was considered for the chloride diffusion coefficients of both the surface-treated layer and the underlying concrete substrate and for the surface chloride content. The validity of this approach was verified with the finite element method and the computation time was only one hundred-thousandth that of the latter. This proposed approach makes it feasible in practice to estimate the probability of corrosion initiation in surface-treated concrete structures via Monte Carlo simulation.

Influence of deicing salt on the surface properties of concrete specimens after 20 years

The low temperature of ice and snow all year round in Sweden leads to the common use of deicing salt to melt the roads, but the splash of the deicing salt on the reinforced concrete (RC) on both sides of the roads brings about the deterioration of the durability of RC components. The chloride ions diffusion coefficient is an important parameter to evaluate the durability of RC. By adopting the rapid chloride migration method (RCM) and replacing chloride ions with iodide ions, the samples of concrete blocks exposed on the side of the highway for 20 years were taken. This is directly beneficial to study the influence of the type, content, and water-cement ratio of mineral additions on the diffusion and distribution of iodide ions in concrete and analyze the surface environmental effect depth of concrete. The influence of chloride ions on the pore structure and microscopic morphology of concrete also were studied by scanning electron microscope-energy dispersive spectrum and X-ray diffractometer. The results show that as the water-cement ratio increases, the surface environmental effect depth of concrete and the diffusion area of iodide ions gradually increase. Silica fume and ground granulated blast furnace slag (GGBF slag) have an impediment to the diffusion of iodide ions, especially with the high volume of the GGBF slag (about 50%), the diffusion of iodide ions is very low. In general, this research is helpful to provide some empirical ideas and suggestions for the manufacturing and durability design of concrete structures in marine environments or deicing salt road environments.

Durability health monitoring during construction of concrete structures in marine environment

A new methodology for durability health monitoring for a bridge structure during construction was developed by monitoring concrete's saturated electrical resistivity (ρS), rapid chloride permeability (RCP), and the apparent chloride diffusion coefficient (DAP) indices. Results were compared with same durability indices collected previously from in-service bridges located along the Gulf of Mexico (Florida, USA, and Yucatan, Mexico). Excellent correlations were found between ρS versus RCP, ρS versus DAP, and RCP versus DAP from present and previous investigation data. Empirical models obtained corroborate that ρS test is feasible to use, instead of more complicated and expensive testing, for structural health monitoring for quality control/assurance during construction.

Analysis of corrosion risk due to chloride diffusion for concrete structures in marine environment

The chloride-induced steel corrosion is one of the main causes of deterioration for reinforced concrete structures exposed to marine environments. The chloride ingress into reinforced concrete structures is even more complex since it depends on random parameters linked to transport and chemical properties of materials, which results in variability of corrosion initiation. This variation raises the need of statistical approaches to evaluate the risk of corrosion initiation due to chloride ingress. To address this issue, we use sensitivity analysis to identify the influence of input parameters on critical length of time before corrosion initiation predicted by our chloride diffusion model. Exceedance probabilities of corrosion initiation time given that input parameters exceed certain thresholds were also calculated. Results showed that the corrosion initiation time was most sensitive to: chloride effective diffusion coefficient De in concrete, that is a parameter controllable by relevant stakeholders; surface chloride concentration Cs, a non-controllable parameter depending on surrounding conditions. Reducing the chloride diffusion coefficient enables us to postpone the maintenance of structures. However, the interaction between controllable parameters and non-controllable surrounding conditions was revealed influential on the reliability of results. For instance, the probability that corrosion initiation time exceeds 15 years given an effective diffusion coefficient (De) equal to 0.1 × 10−12 m2⋅s-1 can vary from 19 to 41% according to stochastic variations of chloride concentrations (Cs) values. Postponing the corrosion initiation time was combined with a decreasing probability of its occurrence.

Prediction of surface chloride concentration of marine concrete using ensemble machine learning

This paper develops and employs an ensemble machine learning (ML) model for prediction of surface chloride concentration (Cs) of concrete, which is an essential parameter for durability design and service life prediction of concrete structures in marine environment. For this purpose, a database containing 642 data-records of field exposure data of Cs (along with the associated mixture proportion parameters, environmental conditions and exposure time) is established based on extensive literature surveying, which covers splash, tidal, and submerged zones in various areas in the world. The database is used to train five standalone ML models, that is, linear regression (LR), Gaussian process regression (GPR), support vector machine (SVM), multilayer perceptron artificial neural network (MLP-ANN) and random forests (RF) models, as well as an ensemble weighted voting-based ML model, and subsequently used to compare their prediction performances. It is shown that, by meta-heuristically combining predictions of RF, MLP-ANN, and SVM, the ensemble ML model produces higher accuracy of prediction compared to all standalone ML models tested in this study. The prediction performances of eight conventional quantitative models for Cs prediction are also analyzed based on the testing dataset selected for ML. The results show that adoption of more diverse datasets and consideration of more factors in conventional models can improve their prediction performance. The ensemble ML model established on a large database, can easily consider the twelve influencing factors (which is difficult for conventional models) in the database, and has superior prediction performance, yet better time-efficiency, compared to conventional models.

Coupling effect of corrosion damage on chloride ions diffusion in cement based materials

The durability of concrete structures in marine environment depends on the migration speed of chloride ions in concrete. If the reinforced steel bars in these structures are attacked by chloride ions and begin to rust, these are considered as failure. In general, the diffusion of chloride ions in concrete is analyzed by solving the diffusion equation based on Fick’s law. In the equation, the diffusion coefficient is assumed to be constant. However, novel studies have shown that corrosion damage could take place in concrete due to the formation of Friedel’s salt during the diffusion process. The evolution of corrosion damage not only causes the diffusion coefficient to be a function of time, but also speeds up the migration of chloride ions. This can decrease the durability of concrete structures. However, few related researches have been reported. Close attention to this study was paid to the coupling effect between corrosion damage and the migration of chloride ions. The variation of porosity of cement based materials due to chemical reaction, physical absorption, continued hydration, and corrosion damage was investigated. Then, a new diffusion equation was derived by considering these factors. By virtue of the numerical method, the spatial-temporal distribution of corrosion damage was evaluated, and its effect on the migration of chloride ions was numerically discussed. These results show that corrosion damage could significantly affect the diffusion of chloride ions.

Capillary suction induced water absorption and chloride transport in non-saturated concrete: The influence of humidity, mineral admixtures and sulfate ions

Concrete structures in marine environments are gravely jeopardized by chloride attack caused by capillary suction. To investigate the erosion of concrete induced by capillary suction under various factors, seawater and NaCl-Na2SO4 solution were used as corrosive solution to obtain the evolution law of water absorbed amount and chloride content in concrete with different water to binder ratio, fly ash and slag dosages and internal relative humidity. The results show that the decrease of internal relative humidity leads to the increase of seawater absorbed by capillary suction in a brief period, and boost rapid growth of chloride content in surface of concrete. For early age (28 d) concrete specimens, when the fly ash dosage is 0–30% or the slag dosage is 0–50%, the water absorption rate and chloride content of concrete are more likely to drop with the dosage increasing. Furthermore, under short-time capillary suction condition, SO42− has a minor impact on water absorption of concrete, while slightly increases the chloride content. However, the chloride content does not evolve coincidently with the change of SO42− concentration. Moreover, within a brief exposure period, the chloride content linearly develops with absorbed sweater amount, and it is inappropriate to use chloride diffusion coefficient to reflect the chloride transport rate of concrete under capillary absorption effect.

Evaluation of chloride ion penetration through concrete surface electrical resistivity of field naturally degraded structures present in marine environment

As reinforcement corrosion due to chlorides action is the main cause degradation of reinforced concrete structures in marine environment, concrete electrical resistivity has been used as a non-destructive methodology in order to evaluate the service life of these structures, since it is a simple and fast field methodology that presents confiable results. At this point, many works have been carried out in order to stablish a correlation between concrete electrical resistivity and chlorides penetration. However, observing the literature and standards about this issue it was noted significant differeces between the values presented for stablish this correlation. Furthermore, a significant part of the literature studies were conducted under controlled laboratory conditions, which can differ from the real aggressiveness that a structure is exposed. Thus, this paper presents a new proposal of range values and classes between the chlorides penetration and the concrete surface electrical resistivity, based on the analysis of real chloride profiles from structures present for more than 40 years in different marine aggressive zones under natural degradation. The results shown that standard parameters were close from the values proposed in this work; however a refinement in the range values and the insertion of new parameter classes are necessary for better evaluation of chlorides penetration in concrete structures present in marine environment.

Service Life Prediction of Reinforced Concrete in a Sea-Crossing Railway Bridge in Jiaozhou Bay: A Case Study

Reinforced bar corrosion induced by chloride ingression is one of the most significant threats to the durability of concrete structures in marine environments. The concrete cover thickness, compressive strength, chloride diffusion coefficient, and surface defects of reinforced concrete in the Jiaozhou Bay sea-crossing railway bridge were measured. The temperature and relative humidity in the concrete and the loading applied onto the reinforced concrete were monitored. Based on the DuraCrete model, a revised model for the service life prediction of concrete structures was established, considering the effects of temperature and loading on the chloride diffusion coefficient. Further, the reliability indexes of the reinforced concrete box girder, pier, and platform, located in the marine and land sections, in relation to service lives lasting various numbers of years, were calculated. The measured and calculated results show that the mean cover thicknesses of concrete piers in the marine and land sections are 52 mm and 36 mm, respectively, and the corresponding standard deviations are 5.21 mm and 3.18 mm, respectively. The mean compressive strengths of concrete in the marine and land sections are 56 MPa and 46 MPa, respectively. The corresponding standard deviations are 2.45 MPa and 2.67 MPa, respectively. The reliability indexes of the reinforced concrete box girder and platform in the marine section, under the condition of a service life of 100 years, are 1.81 and 1.76, respectively. When the corrosion-resistant reinforced bar was used in the pier structure in the marine section, its reliability index increased to 2.01. Furthermore, the reliability index of the reinforced concrete damaged by salt fog in the land section was 1.71.

Spatial identification of exposure zones of concrete structures exposed to a marine environment with respect to reinforcement corrosion

In marine environments structures are subjected to a variety of environmental conditions which govern the degradation processes. For reinforced concrete structures these degradation processes (chloride ingress and corrosion) are driven by the availability of oxygen and humidity. Due to the random process of tidal movements it is difficult to determine the spatial boundaries of the major exposure zones related to reinforcement corrosion, namely tidal, splash and atmospheric. In this paper a method is proposed to assess these zones from the interpretation of corrosion potential and resistivity data obtained from on-site measurements performed on reinforced concrete structures in marine environment. A database has been established using measurement results from several piers of the “île de Ré” bridge in France. The robustness of the method was studied considering various climatic conditions representative of the seasons in the West Atlantic coast of Europe.

Damage Layer Evolution of a Breakwater Under Seawater Attack: Testing and Modeling

This paper presents experimental and theoretical methods to study the damage layer evolution of a breakwater made with concrete hollow squares in marine environment. Wetting time was directly related to the performance degradation of the breakwater by observation. The thickness of damage layer was detected by means of ultrasonic testing. Meanwhile, some samples drilled from concrete hollow squares were analyzed by SEM and XRD in order to illustrate the damage mechanism. Subsequently, a theoretical model containing wetting time ratio was established to simulate the damage layer evolution based on Fick’s second law, which could be suggested to predict the service life of concrete structures in marine environment.

Evaluation of service-life prediction model for reinforced concrete structures in chloride-laden environments

Reinforced concrete structures are subjected to several degradation processes that often occur early, especially due to reinforcements corrosion. Therefore, the use of representative models for an accurate service-life prediction of reinforced concrete structures becomes indispensable. Thus, this study is aimed at evaluating the model proposed by Andrade to efficiently predict the chloride penetration in concrete structures. In addition, the input variables of this model, as well as the challenges in obtaining them are analyzed. Andrade’s model was applied in some case studies to verify their efficiency in predicting the chloride penetration in reinforced concrete structures in marine environments. The results indicate that for data with small exposure times, the model yielded similar responses to the chloride penetration in situ, with good results within an error range of 35%, associated with a maximum difference of only 4.6 mm between observed and calculated values. For the data with higher exposure times, the differences were significant, indicating the need for an alteration in order to best determine the increase in surface chloride concentration over time. Thus, it is suggested that the model undergoes modifications, mainly in relation to two fundamental aspects, (i) adopt the growth of the chloride surface concentration over time and (ii) consider the variability of the concrete characteristics and exposure conditions through a probabilistic approach.

Causes of failure in concrete elements buried in lagoon water

The effect of salt attack on reinforced concrete structures in marine environment has become a source of concern to stakeholders in the construction industry. This trend has led to cracks and sometimes failure of structural members that are exposed to this environment. This study investigated the strength performance of concrete elements in lagoon water which is an offshoot of the Atlantic Ocean in Lagos State, Nigeria. A total of ten 150 mm cubes, and ten 150 mm × 150 mm × 600 mm reinforced concrete beams were cast using Portland limestone cement of 42.5-R at 28 days strength of 40 N/mm2 and cured in both fresh and Lagoon water with water-cement ratio of 0.45. Chemical analysis were carried out to determine the concentration of ions. Mechanical tests were also carried out on the concrete elements. The chemical analysis result showed that Calcium (Ca) was the predominant element having 61.62% in the concrete sample cured with lagoon water while concrete sample cured in fresh water had 51.77%. The flexural behaviour of reinforced concrete beams showed that the flexural stiffness of beams were 15.1 N/mm2 and 12.46 N/mm2 in the lagoon and fresh water, respectively. The compressive strength of concrete cubes cured in fresh water was 42.67 N/mm2 while that of lagoon water was 34.22 N/mm2. The preliminary results showed that concrete gained strength at the early stage for reinforced concrete beams buried in the Lagoon and reduced in strength at the early stage for concrete cubes buried in Lagoon. The result of the compressive strength showed that the high presence of salt could have contributed to the cracks and eventual spalling of concrete elements in marine environment.

Assessment of reinforced concrete structures in marine environment: a case study

Abstract This paper presents the results of a series of investigations that were performed on a reinforced concrete bridge structure exposed to marine environment in subtropical weather. Data were obtained by assessing the structural conditions using visual observations, nondestructive evaluations, and laboratory testing in order to define the cause and the level of concrete deterioration due to corrosion. In addition, a probabilistic methodology was used to compute the time of corrosion initiation focusing on reinforced concrete subjected to a similar chloride environment. The initial service life was predicted with a method that employed the use of statistical models of the governing parameters obtained from field data. Results show that this approach could be utilized for assessment of existing and new constructions and/or as a tool for decision-making process during the structural design phase.