Probabilistic modeling of chloride penetration with respect to concrete heterogeneity and epoxy-coating on the reinforcement

The presented article demonstrates the probabilistic method based modeling of the 2D chloride ingress into reinforced concrete structures with respect to concrete heterogeneity and epoxy-coated steel reinforcement. Spatial change of concrete diffusion is assessed through the investigation of random variation of the ability of concrete to resist chloride ingress. Time-dependent chloride concentration at the reinforcement level in both homogeneous and heterogeneous models is comparatively considered taking into account of the influence of reinforcement protection as well as the defects and holidays of the coating. Expansion optimal linear estimation method is exploited to generate a random field for the structure at the mesoscale and correlation length is employed to simplify the modeling process. Preliminary analyses of the built model are conducted in both deterministic and probabilistic solutions under the scheme of the finite element method. Thus, possibility of such analyses is exploited.Web of Science1224art. no. 406

A critical discussion on the usefulness and reliability of mathematical modeling for service life design of infrastructure

In view of the increasing age of existing structures asset managers are becoming more and more interested to have a clearer picture on the actual condition of the complete stock of existing infrastructure as to anticipate on possible maintenance regarding planning and allocation of the financial resources. Consequently, a clear need is emerging for prediction of the condition level over time using mathematical models. Regarding the design of new structures, the current codes are based on traditional options and thus give ample possibilities for alternative options. For instance, at present the significantly different performance of binders is not taken into account. Therefore it is not surprising that in recent years a clear trend can be observed towards the application of mathematical modelling using a probabilistic approach for durability, e.g. the fib Model Code on Service Life Design. In order to allow for prediction of the condition of a structural component over time or to demonstrate equal performance of design solutions, widely accepted mathematical models that describe degradation processes are required. Ideally, such models should be mathematically and physically sound, provide logical and realistic results, understandable and usable for practitioners, and thus to be to a considerable extent foolproof. However, most models include significant pitfalls and limitations which are either not mentioned or not known even to the developer. In addition, in most cases the quantification of the input parameters is not addressed which will undoubtedly result in ‘shopping’. In this respect the use of input values based on expert opinion should be treated with serious caution. In addition it has to be noted that most models have been calibrated on results obtained for laboratory experiments that have been performed under ideal conditions not reflecting situations encountered in practice. Experience has also shown that probabilistic approaches are frequently misused as to support a wrong decision or an execution error (shallow cover depths)

Durability Analysis of Concrete Bridge Deck Exposed to the Chloride Ions Using Direct Optimized Probabilistic Calculation

Durability of reinforced concrete structures is a deeply discussed problem recently. Concrete structures in the external environment are very often affected by chloride ions from de-icing salt or sea water. Chloride ions penetrate through the concrete cover layer of the reinforcement and can cause eventually the corrosion of the steel. However, when estimating the durability of the structure, it is not sometimes possible to express the parameters by constant values; therefore, the probabilistic methods come in handy. Then, the variability of inputs and outputs can be expressed by histograms. Two probabilistic approaches were applied in this task – Monte Carlo simulation with Simulation-Based Reliability Assessment method, which is widely used for such type of problems, and the Direct Optimized Probabilistic Calculation, which is still relatively new type of approach. The result is a comparison of mentioned methods in terms of accuracy on the model of one-dimensional chloride penetration with time independent diffusion coefficient by using the Fick’s Second Law of Diffusion

Aging concrete structures: a review of mechanics and concepts

The safe and cost-efficient management of our built infrastructure is a challenging task considering the expected service life of at least 50 years. In spite of time-dependent changes in material properties, deterioration processes and changing demand by society, the structures need to satisfy many technical requirements related to serviceability, durability, sustainability and bearing capacity. This review paper summarizes the challenges associated with the safe design and maintenance of aging concrete structures and gives an overview of some concepts and approaches that are being developed to address these challenges

Reliability-based analysis of recycled aggregate concrete under carbonation

Durability represents a crucial issue for evaluating safety and serviceability of reinforced concrete structures. Many studies have already focused on carbonation-induced corrosion of natural aggregate concrete (NAC) structures, leading to several prediction models to estimate carbonation depth. Less research is devoted instead on recycled aggregate concrete (RAC), about which limited experimental works exist aimed at assessing the carbonation coefficient in accelerated tests. Additionally, deteriorating processes are subject to uncertainty, when defining materials, geometry, and environmental actions during the service life of structures. This work presents a reliability-based analysis of carbonation resistance of RACs, using experimental carbonation coefficients derived from the literature, and applied in the full-probabilistic method prosed in fib Bulletin 34. Results demonstrate how aggregates replacement ratio and w/c ratio influence the reliability of RAC carbonation resistance

Doctor of Philosophy

dissertationChloride induced reinforcement corrosion is one of the major problems in premature deterioration of several concrete structures such as bridge decks, concrete pavements and substructures in chloride laden environments. In this research, different ternary, binary and control cementitious concrete mixtures are studied for chloride induced corrosion initiation prediction of concrete structures. Diffusion coefficients are one of the primary variables that initiate chloride induced corrosion. The primary objective of the research is focused on investigation of chloride permeability of different cementitious materials and computation of reliable diffusion coefficients from the Chloride Ion Penetration Test (CIPT) and Wenner probe resistivity data using fundamentals of elctrochemistry. Several theoretical equations and methods are applied to compute improved diffusion coefficients of different ternary, binary based High Performance Cementitious (HPC) system. Correlation between the results of CIPT and the Wenner probe also measures their durability acceptance criterion for investigation of long term chlride penetration. This research also investigated electrical conductivity of different cementitius mixtures from the CIPT data and its effect on ternary cementitious systems. The other objective of this research is focused on the formulation of probabilistic corrosion initiation model with inclusion of apparent variation of previously computed HPC diffusion coefficients and the variation of surface chloride concentration with several corrosion resistant steel reinforcements. The distribution of the other governing parameters is generated from either detailed field survey or laboratory experimental investigation. This study shows the variability and sensitivity of estimation of the time to onset of corrosion using the Monte Carlo technique and Simulation Based Reliability Approach (SBRA). Results from this probabilistic analysis estimate the corrosion free service life for the design of concrete structures in harsh chloride environments with respect to methods for diffusion coefficients computation

Probability Model of Corrosion-Induced Cracking Time in Chloride-Contaminated Reinforced Concrete

Corrosion-induced concrete cover cracking caused by chloride ion is an important indication of durability limit state for marine reinforced concrete (RC) structures and can ultimately determine the structural service life. In this paper, considering the random nature of factors affecting the corrosion cracking process, a probabilistic model which expands on the deterministic model of cover cracking time is developed by using Monte Carlo simulation technique. The results showed that the time to corrosion cracking can be modelled by the Weibull distribution. Finally, the probabilistic analysis for the cracking time is applied to an in-site RC bridge girder with four different durability design specifications. It is found that the mean and 90% confidence interval of the cover cracking time will increase with the improvement of durability design level, which means that the difficulty in precise prediction with deterministic model will augment accordingly

The challenge of the performance-based approach for the design of reinforced concrete structures in chloride bearing environment

The performance-based approach, published by the International Federation for Structural Concrete (fib), was applied for the design of a RC element in a marine environment, with corrosion resistant reinforcement, to analyse the potentiality of the model as well as the possible reasons which limit its use. Results showed that the fib model allows to compare different solutions and to consider the benefits connected with the use of preventative measures. However the definition of reliable values for some input parameters, as the critical chloride threshold for corrosion resistant reinforcement, is demanded to the designer and this aspect clearly limits a widespread use

A NOVEL PROBABILISTIC FRAMEWORK OF RC CORRODED STRUCTURES UNDER DYNAMIC LOADING

Steel corrosion in reinforced concrete structures can lead to severe deterioration damage under static and seismic loads. In practice, it is essential to mitigate failure risk by quantifying the extent of damage and simulating the structural response of damaged structures. However, numerical modeling of the dynamic behavior of corroded structure is challenging due to high nonlinearity of the problem and its multidisciplinary nature. In addition, corrosion damage exhibits various sources of uncertainty that impede accurate deterministic modeling of the dynamic response of RC structures. Therefore, this study presents a simplified framework, to simulate the non-linear response of corroded structures under seismic excitation, in a statistical setting. The presented scheme employs set of state-of-art experiments and numerical investigations of corrosion effect and response to capture the generic non-linear response. The presented scheme is utilized to conduct reliability analysis for corroded structures under earthquake loads by incorporating different sources of uncertainties associated with the used mathematical models and model parameters. The power of the suggested probabilistic scheme is illustrated on two simulated structures, where two different statistical properties are considered; the initial statistical parameters and a real-time monitored statistic for the rate of corrosion

Tensile behaviour of pitting corroded steel bars:Laboratory investigation and probabilistic-based analysis

Localised corrosion in steel bars has been a long-standing issue in the durability of reinforced concrete structures, but a comprehensive scheme for the analysis of pitting corroded steel bars, especially with respect to the deformation capacity, is not currently available. In this study, the morphological characteristics of 27 pitting steel bars were captured using a 3D scanner. The measured data were used to establish the probability distribution model of the cross-sectional areas of the corroded bars. Uniaxial tensile tests were conducted, and the evolving deformation field of the corroded bars was recorded through Digital Image Correlation (DIC). Based on the 3D reconstructed model and DIC results, an analytical method for evaluating the mechanical properties of pitting steel bars was developed and validated. The results show that the two-component Gaussian mixture distribution model outperforms conventional unimodal distribution models. Comparison of the analytical results with experimental data demonstrates that the proposed procedure is capable of predicting not only the ultimate strength but also the gauge length-dependent ultimate strain of corroded bars. Additionally, there exists a strengthening effect in the ultimate stress at the critical sections and this effect should not be ignored for accurate predictions.</p