Durability Design Of Structures Research Articles

Analysis and Zonation of Freeze-Thaw Action in the Chinese Plateau Region Considering Spatiotemporal Climate Characteristics

Concerns about the durability of transportation infrastructure due to freeze-thaw (F-T) cycles are particularly significant in the Chinese plateau region, where concrete aging and performance deterioration pose substantial challenges. The current national standards for the frost resistance design of concrete structures are based predominantly on the coldest monthly average temperature and do not adequately address the comprehensive effects of the spatiotemporal variance, amplitude, and frequency of F-T cycles. To address this issue, this study introduced a spatiotemporal distribution model to analyze the long-term impact of F-T action on concrete structures by employing statistical analysis and spatial interpolation techniques. Cluster analysis was applied to create a nationwide zonation of F-T action level from data on the freezing temperature, temperature difference, and the number of F-T cycles. Furthermore, this study explored the similarity between natural environmental conditions and laboratory-accelerated tests using hydraulic pressure and cumulative damage theories. A visualization platform that incorporates tools for meteorological data queries, environmental characteristic analyses, and F–T action similarity calculations was designed. This research lays theoretical groundwork and provides technical guidance for assessing service life and enhancing the quantitative durability design of concrete structures in the Chinese plateau region.

Prediction of concrete abrasion depth and computational design optimization of concrete mixtures

The failure of concrete for hydraulic structures due to the excessive abrasion depth has caused great economic losses. Despite the tremendous work that has been done, the durability design of hydraulic concrete structures concerning abrasion damage is still a difficult task, especially with a long service life aiming at economic benefit and environmental sustainability. In this paper, machine learning methodologies including random forests (RFs) and artificial neural networks (ANNs), are used to establish prediction models based on concrete mixture proportions, curing age, and hydraulic conditions. Furthermore, RF models are coupled with multiple objective particle swarm optimization (MOPSO) algorithms to perform computational design optimization of concrete mixtures. The optimal solutions are generated based on 5000 randomly generated mixture proportions, among which three optimal designs of concrete mixtures are selected to guide field applications on account of concrete durability requirements and economic benefits.

Effect of ITZ on chloride ion transport in recycled aggregate concrete: Analytical and numerical studies

The weaker ITZ is one of the significant differences between recycled concrete and ordinary concrete. How the weaker ITZ between recycled aggregate and mortar in recycled concrete affects the transport mechanism of chloride ions has become the main obstacle to the large-scale promotion and recycling of demolished building waste. To tackle this issue, a novel equivalent single-phase analytical method was proposed and a series of numerical simulations with different ITZ distributions and characteristics were carried out. The research results indicated that the transport of chloride ions in recycled aggregate concrete was primarily controlled by the diffusion coefficient, volume, and distribution of the ITZ (mainly affected by recycled aggregates). The current analytical methods effectively described the aggregate blocking effect and ITZ effect. The research results revealed that the addition of recycled aggregate within a certain range had little effect on chloride ion transport (the difference in the effect of 30 % and 35 % recycled aggregates addition on chloride ion transport was within 5 %). However, once the volume fraction of aggregates exceeded the threshold, the transfer rate of chloride ions increased sharply. Furthermore, the uniform mixing of recycled aggregates was crucial. As the ITZ non-uniformity coefficient increased, the ITZ diffusion coefficient increased. The weaker ITZ of recycled concrete amplified the impact of concrete cracks, ITZ-crack channels of chloride ions were formed even if minor cracks developed. Current research provided technical support for the durability design of recycled concrete structures.

Deterioration law and life prediction of aeolian sand concrete under sulfate freeze-thaw cycles

To study the deterioration law of aeolian sand concrete (ASC) under the coupling effect of sulfate freeze-thaw, this paper uses aeolian sand as a substitute for river sand to prepare ASC with different replacement rates (0%, 20%, and 100%). Freeze-thaw cycle (FTC) tests are conducted in different salt solution environments (5% Na2SO4, 10% Na2SO4, and 5% Na2SO4 + 3.5% NaCl) to analyze the changes in physical and mechanical properties, and the mechanism of performance degradation of ASC is analyzed by SEM, XRD and NMR. The results show that incorporating aeolian sand significantly improves the salt-freeze erosion resistance of concrete, and when the content is 100%, the impact on salt-freeze erosion on macroscopic properties such as mass loss and compressive strength is minimized, signifying the salt-freeze erosion resistance is the best. During the FTCs, the relative dynamic elastic modulus of concrete initially increases and then decreases, while the trend in mass loss rate reverses. SO42- and Cl- in the salt solutions react with the hydration products to form calcium vanadate, gypsum, and Friedel salts. During the initial stages of FTCs, erosion products fill the matrix pores, increasing the compactness of the concrete, which positively affects macroscopic properties. As the FTCs progresses, ice crystals and excessive erosion products accumulate, resulting in a further expansion of internal pores and cracks in concrete. Consequently, the ratio of harmful to beneficial pores continues to increase, resulting in freeze-thaw damage. After 200 FTCs, in the 5% Na2SO4 + 3.5% NaCl erosion medium, the internal cracks in aeolian sand concrete get bigger and the holes get larger, causing the most damage and deterioration. Different degradation indices are used to predict the residual lifetime of ASC based on a Wiener random probability distribution. The Wiener stochastic process effectively predict the lifetime of ASC under the coupling effect of sulfate FTCs, with the compressive strength loss rate as the most sensitive degradation index. Among them, for ASC-0, ASC-20, and ASC-100 in the 5% Na2SO4 + 3.5% NaCl environment, the maximum FTCs, based on the compressive strength loss rate, are 198, 206, and 213 times, respectively. This study could provide a theoretical foundation for the durability design of concrete structures in cold regions and other salt-frozen regions within Northwest China.

Durability design and construction enhancing of concrete structures in mesoscopic approach: A case study of a large-scale anchorage structure

The durability challenges in concrete infrastructure are complex, with difficulties in considering the multiscale material variation and multiphysics deterioration mechanism during long-term service. This study aims to investigate the structural durability from material scale and predict the probabilistic evolution of structural performance by numerical approach. This paper considers the influence of concrete mesostructure by mesoscopic modeling. For the actual large-scale concrete structure, the different durability problems and different environmental exposures are investigated comprehensively in numerical approaches. Based on the evaluation of reliability indices on structural durability, suggestions are proposed for the structural design and detailed protective measures. With the simulation with 0.1 mm element size and 3-hour time step, the durability deteriorations on the anchorage structure of the Shiziyang Link Project are analyzed, revealing chloride ingress depths, carbonation depths, and the occurrence of corrosion. For the atmospheric zone with a 50 mm concrete cover, carbonation is the governing factor leading the reinforcement corrosion, and the extreme frontal depth can reach 59.4 mm. For the splashing and tidal zone, the carbonation with an extreme depth of 53.0 mm is the major concern for durability, but the 70 mm concrete cover is thicker to protect the structure from local corrosion. For the immersed zone over 10 m underwater, the chloride ingress depth can reach 70 mm thickness of concrete cover after short service. By comparing the depth distributions with the thickness of the concrete cover, the failure probabilities of reinforcement corrosion of three zones can reach 65.5%, 0.0%, and 100%, respectively, after the 100-year service. To meet the restricted durability limit state requirement with under 1% of target corrosion probability, the service lives of three zones range from 6.1 years to over 100 years. The improvement solutions are presented and evaluated for anchorage structural durability. The change of aggregates from rounder shapes to slender shapes can reduce the deterioration depth by about 2.4%, and the probability of reinforcement corrosion under concrete cover can be reduced a lot. For the concrete joint, the recommended seal takes advantage of these basic types, and its resistance to the local carbonation in the joint is also verified by comparison.

How standards support sustainability of cement and concrete in Europe

Until now, the durability design of concrete structures mainly uses a concept in which the performance is verified primarily with Deemed-to-Satisfy (DtS) rules (concrete composition, concrete cover) based on experience. A new concrete durability concept has been developed named Exposure Resistance Classes (ERC) system. The ERC-concept is discussed as an example of a performance-based approach together with the latest development in cement standards in Europe. For solving future challenges, performance concepts are seen as an opportunity to substitute prescriptive approaches by giving more flexibility in applying new technical solutions. The challenge will be to come up with an appropriate mix of descriptive regulations and performance-related approaches. Further developments in cement and concrete standardisation should provide simple and robust rules for most applications with low or moderate requirements and appropriate and safe solutions for applications under severe conditions (performance-approach for durability).

A copula approach in the probabilistic evaluation of chloride ingress process for coastal concrete structures

One of the most prevalent causes of reinforced concrete (RC) structural deterioration is chloride-induced corrosion. This paper is concerned with a novel approach to assess the chloride ingress process for coastal concrete structures under consideration of environmental effects. Firstly, the chloride diffusion process model for one-dimensional (1-D) and two-dimensional (2-D) concrete and the copula theory are introduced. Secondly, the climate data from the National Meteorological Center of China are investigated. Dependencies between temperature and humidity are described with a dedicated copula. Meanwhile, the results are analyzed regarding the geographical variations along the coastline. The critical environmental factors governing the diffusion process are identified and discussed. Finally, the feature of adopting the copula in modeling the environmental characteristics is highlighted. The work could significantly improve the durability design of coastal structures in China. A copula approach is developed to capture dependencies that are difficult to quantify from a physical perspective, including their uncertainties. Comparison to traditional methods shows the advantages clearly.

Stray current induced chloride ion transport and corrosion characteristics of cracked ultra-high performance concrete

Ultra-high-performance concrete (UHPC) is a strong, durable, and corrosion-resistant material that is poised to revolutionize construction in complex environments, such as the deep sea and underground. However, the formation of cracks of UHPC during service and the occurrence of stray currents in underground stations and tunnels greatly accelerate the transport of chloride ions, posing a threat to the safety of underground construction. Here, we used the rapid chloride migration (RCM) method to study the effect of stray current in cracked UHPC. Essentially, electric field accelerates chloride ion transport in cracks by increasing ion transport in the uncracked zone. The wider the crack, the more severe the corrosion of steel fibers, which affects the pore structure of UHPC and leads to an increase in the diffusion coefficient in the uncracked area. In addition, area normalization was employed to precisely monitor the chloride ion concentration in the cracks, which was validated by numerical simulations. Finally, microscopy and atomic force microscopy (AFM) showed that larger crack widths led to deeper corrosion and more severe steel fiber corrosion in UHPC. These results have important implications for the durability design of UHPC structures in stray current environments.

Experimental Study on the Sulfuric Acid Corrosion Resistance of PHC Used for Pipe Pile and NSC Used in Engineering

In order to compare and investigate the sulfuric acid corrosion resistance of concrete for PHC pipe piles and two kinds of concrete commonly used in engineering, acid accelerated corrosion tests were conducted on specimens with three different strength grades of C30, C50, and C80 in a sulfuric acid solution with pH ≈ 0.85. The appearance of the specimens was observed, and the changes in mass loss percentage, corrosion depth, and stress–stain curves under uniaxial compressive loading were calculated and obtained with the corrosion time. From the comparison of corrosion depth and mass loss percentage of the concrete specimens with three different strength grades of C30, C50, and C80, it was found that the higher the strength grade of the concrete, the more severe the corrosion degree. The shapes of the stress–strain curves of three different strength grades of concrete specimens were basically the same. As the corrosion time was prolonged, the peak stress and the elastic modulus of concrete decreased. From the perspective of long-term corrosion, C80 specimens had a relatively smaller percentage of peak stress loss and a stronger resistance to peak stress loss. The research results provide references for the durability design of concrete structures and the prediction of concrete’s service life in a sulfuric acid environment.

High Cycle Fatigue Property of Al–Mg–Sc–Zr Alloy Fabricated by Laser Powder Bed Fusion

Laser powder bed fusion (LPBF) of high‐strength Al–Mg–Sc–Zr alloy possesses great potential application in the aerospace industry. However, fatigue performance has become a very important issue in the safety and durability design of engineering structures. Herein, the high cycle fatigue property of LPBF‐fabricated Al–Mg–Sc–Zr alloy and its correlation with defects, microstructure, and precipitated phases are studied. The LPBF‐manufactured Al–Mg–Sc–Zr alloy appears heterogeneous structure composed of equiaxed grains at the molten pool boundary and columnar grains at the inner of the molten pool. After aging treatment (325 °C/4 h), the nanosized Al3Sc intragranular particles and Mn‐rich intergranular particles are precipitated, leading to more difficult movement of dislocations that favors the fatigue strength. The ultimate tensile strength of the samples after aging treatment is 507.05 MPa and corresponding 107 cycle fatigue strength (R = −1) is 106 MPa. The fracture morphology of the fatigue specimens shows that the fatigue cracks start from the surface defects with strong stress concentration, especially the lack of fusions, and then expand through the surplus part.

Compressive anisotropy effects and crack evolution mechanisms of 3D5d braided composites induced by thermo-oxidative ageing

Ageing cracks and loading directions will affect mechanical behaviors of thermo-oxidative aged 3D braided composites. Here we report ageing crack propagations, compressive responses, in-situ strain evolutions, full-field damage distributions and crack evolution mechanisms of aged three-dimensional five-directional (3D5d) braided composites along out-of-plane (OP) and in-plane (IP) loading based on X-ray micro-computed tomography and digital image correlation technique. Ageing cracks are distributed at both axial ends that corresponding to the yarn arrangement and extend to the interior with the increase in ageing time. Compressive modulus, strength, retention rate and damage mode show ageing weakening behaviors and anisotropy effects. Strain distributions exhibit structure correlation. Ageing cracks affect the surface strain and damage distributions but not internal shear modes during OP loading. Yarn arrangement affects damage evolution and accumulation. Ageing cracks change the damage evolution path in both directions. The synergistic effect of ageing crack with IP loading is greater than that with OP loading. It is expected that this work can provide a clear guideline for the structural optimization and durability design of 3D braided composites.

Service life of RC seawall under chloride invasion: A theoretical model incorporating convection-diffusion effect

This paper presents a theoretical approach, which comprises the chloride transportation model and cover cracking model, to predict the service life of RC seawall under chloride invasion. The chloride transportation model combined the Fick's second law and Darcy's law to model the convection-diffusion of chloride ions in the RC seawall. The governing equation for chloride migration in the RC seawall is solved with the separation of variables technique. The proposed model is validated by comparing with a corresponding finite difference solution and the experimental results. The mechanical model that represents the cracking of the concrete cover induced by the expansion pressure of the corrosion products is finally developed to predict the service life of the RC seawall under chloride invasion. Parametric studies are performed to illustrate the effects of convection-diffusion and other key variables on the chloride ions transportation and service life of the RC seawall. The results reveal that the convection effect substantially accelerates the chloride penetration process in the chloride gradient descent direction while inhibits the penetration in the opposite direction. The proposed analytical solution in conjunction with the mechanical model provides a theoretical approach for predicting the service life of RC seawall, which can be used to aid durability design of coastal structures.

Durability Design of Concrete Structures Under Reinforce-ment Corrosion

Traditionally, the durability design of concrete structures is
 based on implicit rules (minimum concrete cover, maximum
 water/cement ratio, crack width limitation, etc.). The research on
 concrete durability during the last decades has produced a reliable
 basis for information on deterioration processes. Based on this
 knowledge, it is possible to start incorporating durability in the
 design of concrete structures. Standard reliability methods were
 used to evaluate time dependent reliability of concrete structures
 under corrosion attack.

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.

Development of a low-alkalinity seawater sea sand concrete for enhanced compatibility with BFRP bar in the marine environment

To enhance the durability performance of Basalt Fiber Reinforced Polymer (BFRP) bar reinforced Seawater Sea Sand Concrete (SWSSC) structure components in the marine environment, this paper investigated the feasibility of reducing SWSSC alkalinity to improve its compatibility with BFRP bars. The low-alkalinity ternary mixtures were designed with ordinary Portland cement (OPC), silica fume (SF) and fly ash (FA) through the simplex centroid design method. The evolutions of micro-morphology and hydration phase were characterized by isothermal calorimeter, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and thermogravimetric analysis. The added SF and FA inhibit the formation of AFm phases and Friedel's salt, and consume the Portlandite content in seawater cement paste. Exposure in the marine environment can lead to magnesium and sulfur abundant zonation in the low-alkalinity SWSSC. The durability performances of BFRP bars reinforced SWSSC columns are evaluated through accelerated aging tests in a simulated marine environment at 55 °C. The tensile strength degradation of BFRP bars embedded in low-alkalinity SWSSC is significantly mitigated due to the less alkaline and less moist internal environment. After 180-day accelerated aging, the tensile strength retentions of BFRP bars wrapped by low-alkalinity and normal SWSSC are higher than 70% and less than 24%, respectively. After accelerated aging in seawater, the load-bearing capacity of BFRP bars reinforced low-alkalinity SWSSC column slightly improves and the ductility remains unaffected. Meanwhile, the ductility of BFRP bars reinforced normal SWSSC column is reduced by about 30% after conditioning. The research outcomes can serve as a solid base for the durability design of BFRP-SWSSC structures in the marine environment.

Machine learning algorithms in the environmental corrosion evaluation of reinforced concrete structures - A review

Accurate corrosion assessment of reinforced concrete (RC) structures is expected to improve the service life and durability of structures. However, traditional evaluation methods rely on simple regression and assumption models, which are easy to lead to unreliable evaluation results. The time-consuming and complex calculations in corrosion assessment are particularly suitable for machine learning (ML) and have already been deeply affected by the application of existing ML algorithms. The review analyzes recent ML methods for corrosion assessment of RC structures. These algorithms have recently had a significant impact on the estimation of the corrosion process, significant mechanical properties and durability of RC structures. In addition, some challenges that have emerged in corrosion evaluation and could be solved by ML algorithm are discussed critically. Through the detailed analysis of the challenges and future directions, researchers and engineers related industry will gain vital insight on the sustainable durability design of RC structures.

Using a geochemical model for predicting chloride ingress into saturated concrete

Chloride ingress into concrete was simulated based on a geochemical model that includes Fick's second law for transport phenomena and thermodynamic equilibrium, kinetics treatment and surface complexation for chemical phenomena. The geochemical model was validated by comparing the numerical results and experimental data (extracted from the literature) for CEM II concrete exposed to sodium chloride, potassium chloride, magnesium chloride and calcium chloride solutions. The geochemical model was then applied to investigate the influences of different chloride solutions. The results showed that exposure to magnesium chloride solution led to the greatest amount of Ca2+ leaching. Relationships between the total chloride content (TCC) and the free chloride content (FCC) of concrete were established. Increasing the exposure time of the concrete was found to lead to a decrease in chloride binding capacity. The proposed correlations allow determination of the FCC or the TCC of concrete when one of the two is known. The geochemical model was also verified by predicting the chloride content of a CEM III concrete bridge submerged in seawater after 17 and 34 years. With numerous applications, the geochemical model seems a reliable tool for the durability design of concrete structures exposed to chloride environments.

Statistical creep failure time of unidirectional carbon fiber reinforced plastic under bending load

Our developed accelerated testing methodology (ATM) based on the matrix resin viscoelasticity for the creep and fatigue failure life prediction of fiber reinforced polymers (FRP) was applied to the statistical prediction of long-term creep failure life for the longitudinal bending of unidirectional Carbon fiber reinforced plastic (CFRP) laminates which is an important basic item for the durability design of CFRP structures used for aircraft and others. As results, the statistical creep failure times measured under several constant bending loads at an arbitrary temperature for unidirectional CFRP laminates were agreed with the predicted results obtained by substituting the matrix resin viscoelasticity and the flexural static strengths of CFRP laminates statistically and easily measured at various temperatures into the formulation of ATM. The long-term creep strength under bending load at an arbitrary temperature predicted were compared with that under tension load obtained by our previous paper. It was clear that the creep strength under bending load degreases drastically with increase in time and temperature comparing with that under tension load; therefore, the effect of time and temperature on the creep failure life under bending load is larger than that under tension load.

Fatores que afetam a modelagem probabilística da vida útil de estruturas de concreto armado expostas a ambientes marinhos

Abstract Concrete durability design has received increasing importance recently, with specifications moving from prescriptive to performance based. In performance-based approaches, it is essential to evaluate and calibrate service life models capable of reliably representing the phenomenon that triggers the degradation process. This paper aims to discuss the main concepts related to the probabilistic service life modeling of reinforced concrete structures under chloride environments, considering the application of different prediction models. Through numerical analysis, parametric differences among chloride penetration models are evidenced, and the results, their variability, and the admitted failure conditions are analyzed. An overview of the current scenario of the durability design of concrete structures is presented. Aspects associated with characteristic service life, the definitions of durability limit states, and their respective target failure probabilities are discussed.

Explicitly Assessing the Durability of RC Structures Considering Spatial Variability and Correlation

The durability design of reinforced concrete (RC) structures that are exposed to aggressive environmental attacks (e.g., corrosion due to chloride ingress in marine environment) plays a vital role in ensuring the structural serviceability within a reference period of interest. Existing approaches for the durability design and assessment of RC structures have, for the most part, not considered the spatial distribution of corrosion-related structural properties. In this paper, a closed-form approach is developed for durability assessment of RC structures, where the structural dimension, spatial variability, and correlation of structural properties such as the concrete cover thickness and the chloride diffusion coefficient are taken into account. The corrosion and crack initiations of an emerged tube tunnel segment that was used in the Hong Kong-Zhuhai-Macau bridge project were assessed to demonstrate the applicability of the proposed approach. The accuracy of the method was verified through a comparison with Monte Carlo simulation results based on two-dimensional random field modeling. The proposed method can be used to efficiently assess the durability performance of RC structures in the marine environment and has the potential to become an efficient tool to guide the durability design of RC structures subjected to corrosion.