Service Life Models Research Articles

Developments in defining exposure classes for durability design and specification

AbstractDurability design and service life modeling of concrete structures rely on environmental exposure classes based on the prevailing deterioration mechanisms. International standard environmental exposure classes, for example, those found in the fib Model Code 2010 and ISO 22965‐1:2007 are predominantly based on European environmental conditions. Although these exposure classes are more suited to the prescriptive design for durability, they may also be adapted to performance‐based design. For more complex design philosophies such as limit state design using partial factors, the generalizations of the standard exposure classes cannot be suitably employed and therefore a more rigorous characterization of the exposure environment is required. The standard exposure classes in the fib Model Code 2010 as well as various national codes from different regions of the world are critically reviewed, and their limitations highlighted. Based on the review, updates to the standard exposure classes for inclusion in the fib Model Code 2020 are proposed. This paper summarizes the work of TG8.8 WP3 (Commission 8: Durability, Task Group 8.8: Common approaches, Working Party 3: Exposure Zones) and represents the view of the Working Party members.

Investigations of accelerated methods for determination of chloride threshold values for reinforcement corrosion in concrete

ABSTRACT Testing the critical chloride content (C crit) in laboratory samples or in samples retrieved from structures enhances the understanding of rebar corrosion initiation in concrete and can result in a significant improvement of predicting the residual service life of ageing structures. A possible drawback of test methods for C crit is that they can be time-consuming. In this work, different accelerated methods for C crit testing are studied and compared. It is found that the acceleration method influences the test results. The results are discussed with respect to evaluation of existing structures and service life modelling.

Time-dependent concentration of chlorides at the concrete surface revisited

ABSTRACT Service-life modeling of concrete structures exposed to chlorides has received increasing attention in recent years. Despite developments in understanding the transport phenomenon, most models still have limitations, and their results should be interpreted cautiously. This paper presents a state-of-the-art review of recent advances in time-variant models of surface chloride concentration (Cs ) used as a boundary condition in service-life models, examining the role that boundary conditions can play in service-life estimates. Moreover, an overview of the root causes of variability in experimental results and a critical review of the strengths and limitations of time-variant Cs is provided. The results of numerical studies show that the time-variant boundary conditions considered in this work performed reasonably well with short-term empirical data and matched well with field observations. However, this review highlights the need for long-term field data to validate the performance and reliability of results obtained from service-life models using time-variant boundary conditions.

A Theoretical Framework for Service Life Prediction of Reinforced Concrete Structures in Chloride Environment using Load Factors

Service life modeling of reinforced concrete structures in a chloride environment is mainly performed without considering the loading effects. Different loading effects can produce different service life results. This study presents a theoretical framework for the modeling of the service life of reinforced concrete structures in a chloride environment using loading factors, showing that, depending on the loading nature (either compression or tension), different diffusion results could be obtained. This paper also highlights various approaches to service life modeling, such as the deterministic, probabilistic, and semi-probabilistic, which consider different ways to estimate the service life of reinforced concrete structures in chloride environments. The importance of various distributions for the input parameters in the chloride ingress modeling was examined. The proposed framework includes a procedure to estimate the probability of concrete failure in chloride environments.

Structural lightweight aggregate concrete exposed to marine environment for 5 years

The present paper characterises the chloride penetration into a large array of structural lightweight aggregate concrete (LWAC), after a 5-year exposure period to aggressive marine conditions. The chloride profiles, chloride diffusion coefficients and surface chloride contents were determined and the influence of the main composition parameters and exposure conditions was assessed. Current service life models were evaluated through the estimation of chloride profiles. The results suggest that LWAC can present the same durability as normal weight concrete (NWAC). However, despite having the same chloride diffusion coefficients, the surface chloride content of LWAC tended to be greater than that of NWAC, leading to higher chloride penetration at a given depth. In general, the estimated chloride profiles from existing models did not fit the real results.

The role of service life in Life Cycle Assessment of concrete structures

Abstract In comparative Life Cycle Assessment (LCA) of concrete structures it is of crucial importance to provide the functional equivalence of compared alternatives. Most commonly, the comparison is performed between the structures made of conventional and green concrete mixtures. Since they have different mechanical and durability properties, corresponding structures have different strength and service life. While resolving this problem, two approaches are generally possible: either correction of the functional unit volume or correction of the calculated environmental impacts with compressive strength and duration of service life, if functional unit has the same volume. In this work, in order to assess the effect of service life modeling in LCA, both approaches were tested. As a demonstration, comparison of both slabs and beams made of conventional and high volume fly ash concrete exposed to carbonation was carried out. LCA was performed for 94 different mixtures from reported experimental research and calculated environmental impacts (climate change, acidification, eutrophication, photochemical-oxidant creation, and abiotic depletion of fossil fuels) for both approaches were compared. Results showed that different modeling of service life in LCA can result in totally different, even opposite conclusions. With slightly larger volume of functional unit (7%–20%), all normalized environmental impacts of high volume fly ash concrete structural members were lower for an order of magnitude (6–7 times) compared to those obtained on the basis of the same volume approach. Therefore, drawing conclusions only on the basis of service life modeling with the same volume approach may be misleading. The proper choice of the best alternative should be based on the integrated assessment which includes structural, environmental and cost assessment of the structure as a whole.

Study on Performance Aging of Nonmetal Low Voltage Metering Cabinet Shell in Typical Environmental Conditions

One of the key technologies in the field of smart grid measurement is to make a breakthrough in the detection and evaluation of high availability materials in smart measurement equipment. Under the comprehensive cross action of multi environment, how to combine the nonlinear evolution and mathematical model to analyze the complex environment into the feature combination of multiple single environmental factors, and how to find the key parameter features to express the aging life of materials is the focus and difficulty of the research. On the basis of service life model, the research on protection measures and life assessment technology of smart grid measurement equipment can make the equipment realize wide area application and high availability under worse conditions.

Service Life Modeling of Concrete with SCMs Using Effective Diffusion Coefficient and a New Binding Model

This paper presents a new algorithm that predicts the service life of concrete contains supplementary cementitious materials, SCMs, and determines time of corrosion initiation. The algorithm drives effective diffusivity from an apparent diffusion model, using experimental binding data performed in the lab, temperature, free ion concentration, and carbonation, and generates free chloride profiles for concrete with and without SCMs by using Fick’s law in a finite element model. Adjusting diffusion coefficient at each step of the solution, by addressing the impact of different parameters, simplifies the algorithm and reduces calculation time without jeopardizing the results’ quality. Results generated by the model compare well to the performance of concrete blocks constructed in an exposure site on the east coast of Saudi Arabia. The exposure site hosted five different mixes of Portland cement and SCMs, and the concrete blocks were exposed to harsh weather over the period of two years. Linear polarization and chloride profiling assessed the performance of the mixes against corrosion activities. Lab work identified the performance of the mixes through binding capacity and chloride profiling. Statistical analysis evidenced the accuracy of the model through correlation and regression analysis. Furthermore, a new proposed binding model, produced from binding data in different studies, alters the experimental binding data in the algorithm to decouple the solution from experimental values. The algorithm proves its accuracy when compared to the experimental free chloride profile. The proposed transport model proves that using effective diffusion and binding capacity are enough to generate reliable results, and the effective diffusion can be calibrated with environmental conditions such as temperature, age, and carbonation. Finally, the algorithm presents its features in an object-oriented programming using C# and user friendly web interface.

A Bayesian inference approach for the updating of spatially distributed corrosion model parameters based on heterogeneous measurement data

In many countries concrete bridges are reaching the end of their service-life, showing signs of deterioration, e.g. due to corrosion. Hence, the question arises whether their safety level is still acceptable. To improve the estimate of the safety level, information extracted from different tests, e.g. proof-loading, operational modal analysis, etc., where deflections, strains or accelerations are measured, can be used. Unfortunately, in practice inspection results are often not used directly to improve our knowledge of the degree of deterioration and it is difficult to combine information from different types of tests when making inferences. In this contribution, a methodology is developed and demonstrated in order to update estimations of parameters of service life models for concrete girders subjected to chloride-induced corrosion based on heterogeneous measurement data, with focus on strains measured under proof-loading and modal parameters extracted from ambient vibration tests. A Bayesian framework is adopted, where posterior distributions of the parameters describing the corrosion process are generated based on Markov Chain Monte Carlo sampling. These updated distributions reflect the information on the actual deterioration state of the bridge, which can be extracted from limited data. The updating procedure based on strain and modal data is illustrated by application on a simply supported beam and a case study.

Impacts of reinforcement ratio and fatigue load level on the chloride ingress and service life estimating of fatigue loaded reinforced concrete (RC) beams

High-cycle fatigue loading combined with chloride exposure was studied with a close investigation of reinforcement ratio (1.06%, 1.59%, 2.91%) and fatigue load level (0.2–0.5). This study conducts both, experimentally and service life modeling based on the Monte-Carlo simulation. Results show that: (1) high-value fatigue loads expedite the chloride ingress of compressive concrete; (2) at the load level of ≥ 0.4, chloride ingress of tensile concrete significantly increases and service life decreases ≥ 93%; (3) although reinforcement ratio of 1.59% decreases the chloride ingress of tensile concrete, varying the reinforcement ratio rarely affects the service life.

DETERMINATION OF A RESTORATION PERIODS OF A FRAME INSULATION OF TM ED-118A BY RECOVERY VOLTAGE OBSERVATIONS

Purpose. The aim of the research is to improve the maintenance system of a traction motor (TM) ED-118A by predicting the life of a frame insulation and determining recovery moments while ensuring the lowest unit costs for performing a major repairs of a volume 1 (MjR-1) and permanent repair of a volume 3 (PR-3), taking into account the degree of recovery, using data on the insulation state by the recovery voltage method in the operation process. Methodology. The problem of determining the service life of the frame insulation and the corresponding moments of its recovery for the traction motor is formulated as an optimization problem. The criterion in the task is the minimum of the total unit costs for the implementation of PR-3 and MjR-1 during the period from the last MjR-2 (a major repairs of a volume 2) to the next MjR-2. Findings. The maximum value of the recovery voltage and the value of the integral estimate introduced are indicators characterizing the state of the frame insulation of the TM. As an indicator of the insulation state, an integral estimate is adopted, which is constructed by measuring the recovery voltage. Factories carrying out repairs of frame insulation have different quality of its restoration, which affects the unit cost of restoration and insulation service life. Originality. The optimization procedure takes into account the degree of insulation recovery when performing PR-3 and performing MjR-1. Modeling of the insulation service life and the recovery period of the PR-3 is based on measurements of the recovery voltage of the casing insulation, depending on the mileage. Practical value. The values of the integral indicator considered in the problem, changes in the recovery voltage of the casing insulation in the current measurement procedure, at which MT diagnostics are performed, can be used to predict the service life and simulate the moments of insulation recovery, as well as the maximum values of the recovery voltage in the current measurement procedure in accordance with mileage of a locomotive.

A novel experimental method to determine the critical chloride content in cement-based composites

In reinforced-concrete structural members, the protective passive film on the rebar surface is broken when a critical content of chloride ions (Ccrit) is accumulated at the rebar-concrete interface by diffusing through the concrete cover. The value of Ccrit is often used for determining maintenance schedules and service life modeling of reinforced-concrete infrastructure. A novel method for accurate determination of Ccrit is proposed in this article, which addresses some of the limitations of current practice. For the development of this method, seventeen identical beam specimens, made with reinforced-Strain-Hardening Cementitious Composite (SHCC), were prepared according to the ASTM G109 procedure. The corrosion activity was monitored using various electrochemical techniques to detect the initiation of corrosion. Immediately after corrosion initiation, each specimen was sectioned to determine the chloride contents at multiple points along the rebar-SHCC interface and to observe the depths of the tiny corrosion pits on the surface of the rebars. We found a linear correlation between the chloride content and the average corrosion pit-depth and determined the Ccrit of SHCC as the y-intercept of this linear correlation.

Comparison of procedures for the evaluation of time dependent concrete diffusion coefficient model

The article focuses on approaches for the computation of the input parameters of the time-dependent service-life model for the resistance of High Performance Concrete mixtures (HPC) against chloride ion penetration. The resistance of chloride ion penetration due to corrosion is described by means of diffusion coefficient. The diffusion coefficient is derived from the non-destructive testing method of electrical resistivity based on electrochemistry and following AASTHTO TP-95 specification. The effect of concrete maturity on the diffusion coefficient is taken into account via aging factor. In addition, the application of the least square method is presented and compared with the logarithm-based method in order to approximate the aging factor and reference diffusion coefficient. The quality of approximation of both approaches including the effect of the reference diffusion coefficient selection is also evaluated. Further, the derivation for the computation of model input parameters of both methods is presented. Finally, evaluation of goodness of fit of both approaches is conducted, and recommendation has been proposed via Least Square method and coefficient of determination.

Uncertain time-dependent reliability analysis of corroded RC structures applying three-term conjugate method

Evaluation of reinforced concrete (RC) structures which are subjected to the damaging environmental factors during the service life is critical. The service life model, the effects of environmental factors with their extent of damage during the service period of the structure could be predicted. Various uncertainties that came with this assessment confidence in the results should be taken by a safe margin. Structural reliability methods are one of the best tools to calculate the life model that considers the random properties of parameters. However, if the epistemic and inherent uncertainty of parameters with their time-dependent changes considered, the life model is more reliable. The reinforcement corrosion is the most damaging mechanism that causes the premature degradation of RC structures and substantial economic losses each year. In this work, the time-dependent reliability of an RC beam with chloride-induced corrosion considering epistemic uncertainty via an efficient numerical procedure is developed. Fuzzy time-dependent reliability index has been calculated using α-cut approach based on a hybrid version of genetic algorithm (GA) and particle swarm optimization (PSO), namely HGAPSO applying three-term conjugate reliability method. Results showed that the proposed numerical approach could efficiently and robustly estimate the fuzzy time-dependent reliability index.

Statistics and Artificial Intelligence-Based Pavement Performance and Remaining Service Life Prediction Models for Flexible and Composite Pavement Systems

In their pavement management decision-making processes, U.S. state highway agencies are required to develop performance-based approaches by the Moving Ahead for Progress in the 21st Century (MAP-21) federal transportation legislation. One of the performance-based approaches to facilitate pavement management decision-making processes is the use of remaining service life (RSL) models. In this study, a detailed step-by-step methodology for the development of pavement performance and RSL prediction models for flexible and composite (asphalt concrete [AC] over jointed plain concrete pavement [JPCP]) pavement systems in Iowa is described. To develop such RSL models, pavement performance models based on statistics and artificial intelligence (AI) techniques were initially developed. While statistically defined pavement performance models were found to be accurate in predicting pavement performance at project level, AI-based pavement performance models were found to be successful in predicting pavement performance in network level analysis. Network level pavement performance models using both statistics and AI-based approaches were also developed to evaluate the relative success of these two models for network level pavement performance modeling. As part of this study, in the development of pavement RSL prediction models, automation tools for future pavement performance predictions were developed and used along with the threshold limits for various pavement performance indicators specified by the Federal Highway Administration. These RSL models will help engineers in decision-making processes at both network and project levels and for different types of pavement management business decisions.

Long-term performance of timber-concrete composite systems with notch-screw connections

This paper presents the experimental results of long-term tests performed on six push-out specimens, one timber-concrete composite (TCC) beam with notch-screw connections, and one timber beam. The interface slip of shear connections was evaluated in a constant temperature and humidity environment, and two loading cases (15% and 30% of the ultimate bearing capacity of push-out specimens) were considered. After 342 days of loading, the long-term slip for the push-out specimens with 0.15 and 0.30 loading levels were 0.221 mm and 0.338 mm, respectively. The beam specimens were tested in an uncontrolled indoor environment. The long-term loads sustained by the beam specimens were approximately 18.8% of the short-term flexural capacity. After more than 400 days of loading, the maximum mid-span deflection of the timber beam and TCC were 4.25 and 4.20 mm, respectively. The timber strain and the interface slips of the TCC specimen showed more obvious environmental sensitivity than the mid-span deflection. Three existing creep models and a modified model were adopted to fit the long-term slip curves of the push-out specimens. The modified model showed the best fitting accuracy with the recorded data, and the most reasonable prediction tendency for the whole service life. The final mid-span deflections of beam specimens were predicted by the modified model for the 50-year service life, and the predicted results for the timber beam and TCC were 12.7 mm and 10.1 mm, respectively. These results are in good agreement with the calculation results according to Eurocode 5 and NDS-2018.

A Fuzzy Logic Approach to Preventive Conservation of Cultural Heritage Churches in Popayán, Colombia

ABSTRACT From a decision-maker’s perspective, the management of cultural heritage is a challenging task because of different objectives pursued, the public/private nature of heritage constructions studied, the wide variety of associated values (artistic, historical, cultural, economic) and diverse interests of different stakeholders. Careful consideration of environmental, social and economic factors is crucial in order to predict the functional service life of heritage constructions. This study outlines a new fuzzy system approach based on expert knowledge, which focuses on the serviceability of heritage buildings using a Mamdani fuzzy model. The method input considers 10 intrinsic variables directly related to the vulnerability of buildings and 9 external hazards, classified according to static-structural features and environmental hazards, which are considered useful for defining emergency programs in historical centres in South America (Colombia). The automation of inspection programs similar to the one described here may reduce the consumption of natural resources and benefit a more rational management of future maintenance actions. In general terms, this type of fuzzy logic model approach is designed to serve as an indicator for the future evolution of the functionality of buildings. This research contributes to the study of new service life models applied to heritage buildings in South America.

Heritage, resilience and climate change: A fuzzy logic application in timber-framed masonry buildings in Valparaíso, Chile

Architectural heritage is one of the most essential parts of community well-being; it reflects a complexity of ideas and local cultural values. Currently, new plans or programmes are needed to manage and protect heritage building areas, such as the cities on the Pacific Chilean coastline that are susceptible to natural afflictions. This research intends to apply a functional service life methodology to a new context in Chile: the city of Valparaíso, which represents one of the most excellent examples of late 19th century urban and architectural development in Latin America. The service life model assists a panel of professional experts in making key decisions about heritage building preservation. This research work applied the serviceability method to 25 heritage building constructions (timber-framed masonry) located in Valparaíso. The viability of the system has been verified in previous works and applications in Europe (Spain and Portugal) and the South of Chile (Valdivia). The majority of the sample presents a good functional level, with the exception of just three cases which are positioned in the middle level/grey area (cost and benefits are taken into account and balanced). These case studies should be analysed periodically over time to preserve their functionality. Intervention has been defined as a priority; this information is completely relevant to establishing an approximate periodicity of intervention for this kind of heritage construction and in this kind of context in South America. This work is complemented by a climate change approximation which considers the main possible effects on built heritage located in Valparaíso, Chile. The research work can help stakeholders become involved in the definition of future effective preventive maintenance programmes for heritage building stock.

Study on Yield Mechanical Properties of High Availability Materials before and after Aging for Intelligent Measurement Equipment

One of the key technical research points in the field of smart grid measurement is to make a breakthrough in the detection and evaluation of high availability materials in intelligent measurement equipment. The comprehensive cross-action of multi-environmental stress brings a lot of data, how to find the key parameters in it, and how to analyze the complex environment into the characteristic combination of multiple single environmental factors, and the mathematical model of nonlinear evolution and service life of material aging based on the characteristic expression of the combination, all of the above are the key points and difficulties of the research. On the basis of the service life model, the research on differential protection measures and the study of life evaluation technology for smart grid measurement equipment can enable the equipment to realize wide-area application and high availability under more harsh conditions, which is one of the key points to improve the quality control in NQI system.

Service life assessment of chloride affected bridge located in coastal region of India considering variation in the inherent structural parameters

Deterioration of RC bridges due to chloride induced corrosion is a grave concern worldwide. It occurs essentially, when the reinforcement embedded in concrete is exposed to marine or aggressive environments. Over the past few decades, many studies aimed at determining the parameters influencing the service life of structures affected by reinforcement corrosion. The aim of the present work is to put forward a reliable and simple service life model for predicting the useful life or period of RC bridges affected by chloride ingress and to validate the output of the model with the deterioration of an existing RC bridge structure. The application of the service life model has been done in an Indian bridge in the context of coastal environment. Parametric studies have been conducted in the model for examining the effect of various parameters such as water-cement ratio, reinforcement diameter, cover thickness, type of binder and corrosion rate on the variation of service life of the RC bridge structure. The results of the parametric study explained in a detailed manner so as to get an actual insight of the structural degradation mechanism for structures exposed to chemically aggressive environments.