The structural performance of steel fiber-reinforced concrete (SFRC) members primarily depends on the distribution and orientation of the fibers. Previous experimental studies revealed that the distribution and orientation of fibers are random and hardly controlled during the fabrication process. The centrifugal forming technique may improve the orientation and distribution of steel fibers in hollow circular SFRC piles and increase the shear strength of the piles. Accomplishing this task can lead to the possible replacement of shear reinforcements with steel fibers in piles, thereby improving the demanding productivity that is desired in the pile construction industry by saving considerable time and labor. This paper presents a novel experimental program to (a) develop the casting procedure for SFRC piles and (b) investigate the shear strength of SFRC piles without shear reinforcement compared to that of conventional reinforced concrete (RC) piles with shear reinforcement. With the aid of X-ray technology, different mix proportions and casting methods were investigated to determine the optimum procedure, which produced fiber distributions and orientations in SFRC piles superior to those of RC piles. The centrifugal forming method influenced the orientation of the fibers so that they were oriented in the shear stress direction (i.e., circumferential direction). The loading test demonstrated that the steel fibers effectively worked as shear reinforcement and that the shear capacity increased with the steel fiber content. Moreover, the SFRC piles exhibited stable crack propagation and improved post-cracking stiffness without severe concrete damage compared to that of the RC piles.

Corrosion of reinforcement steel is one of the primary factors leading to performance degradation of bridge structures located in coastal marine environment. To preserve adequate performance levels of RC bridges under traffic loads and a severe airborne chloride environment, frequent maintenance activities are required. These activities increase the total life-cycle cost (LCC). As an alternative to conventional reinforcement, stainless steel (SS) reinforcement can be a promising option to avoid corrosion problems and reduce the maintenance cost. It is necessary to identify appropriate geographical locations where the use of SS rebars proves economical since airborne chloride intensity depends on the meteorological condition and distance from coastline. In this paper, a novel probabilistic method for LCC estimation of RC girders under traffic and airborne chloride hazards is established. The critical distances from the coastline for SS rebar application in RC bridges under different coastal environments in 30 cities in Japan are determined based on the proposed method.

In this paper, a procedure to update the structural reliability considering the effect of spatial steel corrosion distribution is proposed. The covariance matrix decomposition method is applied to simulate the spatial random fields of the associated random variables in the deterioration prediction model. When the observational data at discrete locations on the aging reinforced concrete (RC) bridge structures can be obtained, the spatial random fields are updated by particle filter for stochastic interpolation. Subsequently, the structural reliability of RC bridge structures can be updated simultaneously. As an illustrative example, the reliability analysis of the RC bridge girder considering spatial steel corrosion using the observational data is presented. The observational data from visual inspection results of crack width is used to update the structural reliability.

Chloride-induced steel corrosion is a dominant cause of deteriorated RC structures in marine environments. The distribution of corrosion is found to be highly varied over RC structures. Previous studies reported that the assumption of uniform steel corrosion is an oversimplification, which leads to an error in estimating the structural performance of corroded RC structures. Therefore, it is important to consider the effects of spatial variability associated with steel corrosion for evaluating the structural performance of corroded RC members. Moreover, as RC members are commonly reinforced with multiple rebars, the correlation of corrosion among the rebars can have a great influence on their structural behaviors. The main objective of this paper is to conduct the experimental and computational studies for investigating the effect of spatial localized corrosion of multiple rebars on the structural performance of corroded RC beams.

Corrosion is spatially distributed over RC structures due to several factors, such as different environmental exposure, concrete covers, and concrete qualities. Ignoring the effect of spatial variability is a drastic simplification for the reliability assessment of corrosion-affected RC structures. In this paper, a novel approach is established to assess the reliability of RC girders using finite element (FE) and probabilistic analyses considering the spatial variability of steel corrosion. An experiment was conducted to study the effect of current density on the spatial steel corrosion of RC beams. In the FE model, the spatial variability of steel corrosion was modeled by Gumbel statistics deduced from the experimental data. The results of FE analysis show that using the Gumbel distribution parameters derived from the steel weight loss data associated with higher current density cannot reproduce the non-uniformity of corrosion distribution, leading to an underestimation of flexural failure probability of RC girders.

© 2020 Elsevier Ltd Several parameters during the fabrication process cause segregation and poor orientation of the fibers in steel fiber-reinforced concrete (SFRC) members. With its high flowability and compactability, self-compacting fiber-reinforced concrete (SCFRC) can be used as an alternative to conventional SFRC, as it exhibits improved orientation and lesser fiber segregation. This study aims to investigate (1) the effects of concrete type (i.e., SCFRC versus SFRC), fiber content, and specimen depth on the fiber distribution and orientation and (2) the structural performance of SCFRC and SFRC beams considering their fiber distribution and orientation using X-ray images. The X-ray images showed that owing to the high-flow properties, the SCFRC beams exhibited a lower fiber segregation and better fiber alignment than the SFRC beams. The bending test results demonstrated that the SCFRC beams exhibited better flexural performance than the SFRC beams owing to the improved distribution and orientation of the fibers. Moreover, a finite element (FE) analysis was performed to evaluate the structural performance of the beams considering the varying fiber distribution properties observed in the X-ray images. The FE method could differentiate the superior structural performance of the SCFRC beam from that of the SFRC beam.

© 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group. Reinforced concrete (RC) bridges under traffic loads and a severe airborne chloride environment require more frequent and intensive maintenance activities to preserve an adequate performance level. The use of stainless steel (SS) reinforcement in lieu of carbon steel (CS) reinforcement can be a promising alternative to avoid corrosion problems and reduce the maintenance cost. As the airborne chloride intensity depends on the meteorological condition and the distance from coastline, it is essential to determine the appropriate geographical locations where the use of SS rebar provides economic benefits. The main purpose of this paper is to present a novel approach for identifying the location of RC bridge suitable for SS rebar use considering the hazard intensity associated with the airborne chloride based on the probabilistic life-cycle cost (LCC) analysis. A novel probabilistic method for LCC estimation of RC bridge girders under traffic and airborne chloride hazards is established. In an illustrative example, the suitable location and critical distance for SS rebar application in RC bridges under different coastal environments in Japan are identified based on the proposed method. Sensitivity of LCC to four key parameters including discount rate of money, corrosion rate of SS rebar, concrete cover, and water-cement ratio is performed.

RC bridges near Japan coastal regions deteriorate due to chloride-induced steel corrosion. In such severe airborne chloride environments, RC bridges demand frequent maintenance activities to preserve the desired structural performance. However, maintenance cost causes a surge in their lifetime cost. Resource scarcity is amplifying the need to search for better corrosion-resistance material than carbon steel (CS) rebar. With superior corrosion resistance, stainless steel (SS) rebar can be a better alternative. Nevertheless, its high initial cost raises the initial cost of RC structures. As airborne chloride attenuates with the distance from the coastline, it is essential to develop an approach to integrate the chloride hazard assessment into the life-cycle cost (LCC) analysis for considering cost-effective application of SS rebar. This paper aims to establish a probabilistic LCC method for identifying the suitable distance from the coastline for SS rebar application in RC bridges under an airborne chloride environment.

© 2019 Elsevier Ltd Corrosion of steel reinforcement is spatially distributed over RC structures due to several factors such as different environmental exposure, concrete cover, and concrete quality, among others. Ignoring the effect of spatial variability is a drastic simplification for the prediction of the remaining service life of RC structures. Therefore, it is essential to identify the factors influencing the spatial steel corrosion and structural performance of corroded RC structures. In this paper, an experimental research is conducted to study the effects of main parameters (i.e. current density, concrete cover, rebar diameter, and fly ash)on the spatial variability associated with steel weight loss, corrosion crack, and structural behavior of accelerated-corrosion RC beams using X-ray radiography and digital image processing. The test results showed that low current density (Icorr ≤ 50 µA/cm2)induced highly non-uniform corrosion associated with few large pits and cracks at certain locations while higher current density produced more uniform corrosion and cracks over the beam length. Gumbel distribution parameters were derived from the steel weight loss data for modeling spatial steel corrosion. A novel approach was established to assess the reliability of RC structures using finite element (FE)analysis and probabilistic analysis considering the effects of modeled spatial variability of steel weight loss based on X-ray photographs. Using the Gumbel distribution parameters derived from the steel weight loss data associated with higher current density may underestimate the non-uniformity of corrosion distribution which can lead to an overestimation of the load capacity of corroded RC structures.

© Federation Internationale du Beton (fib) - International Federation for Structural Concrete, 2019. Uniform distribution of fibres which are orientated parallel to the direction of tensile stress is essential to improve the structural performance of steel fibre reinforced concrete (SFRC) members. However, the fibre distribution in concrete structures is hardly uniform due to the effects of many parameters during the fabrication process (vibration, placing methods, concrete moulds, etc.) which can negatively affects their structural performance. The use of self-compacting concrete (SCC) instead of normal concrete can be a good alternative where the fibres can be aligned in the direction of flow without the use of vibration. This paper presents an effort for improving the structural performance of fibre-reinforced concrete members by utilizing the high-flowability and self-placability properties of SCC to achieve better distribution and orientation of fibres. In the experiment, the self-compacting fibre reinforced concrete (SCFRC) was flown into beams and the X-ray image was taken over the whole length of each specimen to investigate the effects of flow distance from the casting point on the distribution and orientation of fibres. In addition, other specimens were also fabricated using SFRC (with normal concrete). The bending tests were performed to observe the flexural performance of SCFRC and SFRC specimens. By the comparison of their structural performance, it was found that SCFRC ones provided better performance due to the more uniform distribution of fibres which were aligned in the flow direction of SCFRC.

© 13th International Conference on Applications of Statistics and Probability in Civil Engineering, ICASP 2019. All rights reserved. Performance of corrosion-affected RC structures depends on the spatial variability of steel corrosion of reinforcing bars. The effect of spatial variability of steel corrosion on the remaining service life of concrete structures is significant. In this paper, an experimental study was conducted to investigate the effect of current density on the spatial variability of steel corrosion. This variability is modeled using Gumbel distribution derived from experiments and incorporated with FE method to estimate the yield loading capacity of RC beams. The results show that using Gumbel distribution parameters derived from the specimens with high current density may lead to an overestimation of load capacity of corroded RC beams.

© Federation Internationale du Beton (fib) - International Federation for Structural Concrete, 2019. Ignoring the effects of spatial variability of steel corrosion can lead to an error in the long-term performance assessment of RC structures. Recent research has been focusing on modelling spatial steel corrosion using experimental data from the corroded RC members by means of the impressed current method. However, researchers have applied a wide range of current density neglecting its effects on the spatial steel corrosion and the reliability of corrosion-affected RC beams. This paper aims to study effects of current density on the spatial steel corrosion and reliability of RC structural beam using finite element analysis. Three RC beams were corroded using current density of 50, 100, and 500 μA/cm2. The spatial growth in steel weight loss in RC specimens was quantified at different corrosion levels using X-ray and image processing techniques. It was found that low current density of 50 μA/cm2 induced more non-uniform steel corrosion than higher levels of current density. Gumbel distribution parameters were derived from the experimental results and used to approximately model the spatial steel corrosion. An illustrative example was provided to study the effect of the modelled steel corrosion associated with low and high current densities on the reliability analysis of a structural RC beam. It was found that the failure probability of the RC beam estimated using the modelled spatial steel corrosion associated with small current density was higher than that associated with high current density.

Since structural performance of corroded RC members primarily depends on localized corrosion damages on their reinforcements, modelling the spatial steel corrosion is important for the long-term performance assessment of RC structures. To achieve this purpose, there is a need to study the time-variant spatial distribution of steel corrosion. The impressed current technique by means of applying current density has been widely used to investigate the effect of steel corrosion on the structural capacity deterioration. It was reported that current density has great influence on the propagation of average crack width, steel corrosion, and structural behavior of RC members. However, the study of the effect of current density on the spatial variability of corrosion and cracking is scarce. Therefore, the main objective of this paper is to study, using X-ray and digital image processing techniques, the effects of current density on the spatial steel corrosion and corrosion cracking of corroded RC beams.

© 2018 Elsevier Ltd Several studies have revealed that the fiber distribution is usually not uniform since many parameters during the fabrication process cause different fiber distributions and orientations within individual steel fiber-reinforced concrete (SFRC) members. This phenomenon results in large scattering in the post-cracking flexural responses among the material characterization specimens. Consequently, when estimating the flexural behavior of SFRC beams, conflicting results are often obtained using only a single constitutive stress-crack opening laws to characterize the material behavior in tension without considering the different fiber distributions and orientations. In this paper, a novel integrated approach is established to estimate the flexural behavior of SFRC beams using both a finite element (FE) method and X-ray imaging. In the prediction approach, a parameter that can be determined using the measured fiber distribution properties from an X-ray image is proposed to consider the variability of the fiber dispersion in each SFRC member. A method is presented for deducing the constitutive stress-crack opening laws using an FE analysis and the proposed parameter from X-ray images. In the numerical FE method, the variability of the fiber dispersion of the individual SFRC beams is determined by identifying the stress-strain relation in each mesh based on the proposed parameter from the X-ray images. The FE method provides better prediction results of the loading capacity for the SFRC beams.

Structural performance of deteriorated reinforced concrete (RC) members depends on the magnitude and location of steel corrosion. Finite element (FE) method has been applied to the structural performance assessment of corroded RC members; however, the difficulty in quantifying cross-sectional area of rebar embedded into the concrete has been reported as a main challenge for conducting the FE analysis precisely. The two main objectives of this paper are to: (1) experimentally investigate the effects of spatial variability associated with steel corrosion on the structural behavior of a corroded RC beam and (2) establish a FE numerical modeling to assess the structural performance of corroded RC beams. In the experimental study, the spatial variability associated with the steel weight loss over the RC beam is quantified using X-ray and digital image processing techniques. This experimental result is used as input data for the FE analysis. The proposed model provides good agreement with the test results.

The material properties of concrete structures and their structural dimensions are known to be random due to the spatial variability associated with workmanship and various other factors. This randomness produces spatially variable corrosion damages, such as steel weight loss and corrosion cracks. The structural capacity of reinforced concrete (RC) members strongly depends on the local conditions of their reinforcements. Modelling the spatial variability of steel corrosion is important, but steel corrosion in RC members can only be observed after severely damaging the concrete members. To understand the steel corrosion growth process and the change in the spatial variability of steel corrosion with time, continuous monitoring is necessary. In this study, X-ray photography is applied to observe steel corrosion in RC beams. The steel weight loss is estimated by the digital image processing of the X-ray photograms. The non-uniform distribution of steel weight loss along rebars inside RC beams determined using X-ray radiography and its correlation with longitudinal crack widths are experimentally investigated.

The severity of damage due to corrosion on reinforced concrete (RC) structures primarily depends on the magnitude and location of the steel corrosion. A finite element (FE) method has been used to evaluate the structural performance of RC members subjected to reinforcement corrosion. However, the difficulty in quantifying the residual rebar cross-sections in the concrete has been reported as the primary challenge in providing important parameters for modeling the corrosion damages on the steel reinforcement and concrete. The three primary objectives of this paper are to (a) experimentally investigate the effects of the spatial variability in the steel corrosion on the structural behaviors of five corroded RC beams, (b) establish a FE method to assess their deteriorated structural performances, and (c) develop Gumbel distribution parameters to estimate the spatial variability of corrosion for the rebars. In the experimental study, the spatial variability in the steel weight loss along the corroded rebars in the concrete medium was quantified using X-ray and digital image processing techniques. For the FE analysis, the experimental steel weight loss data was used for modeling the residual steel cross-sections, reduced concrete strength, and deteriorated bond interface. The flexural capacity obtained from the simulated beams is in agreement with experimental results. (C) 2016 Elsevier Ltd. All rights reserved.

The performance of corrosion-affected RC members depends strongly on localized damages of reinforcement. Therefore, modeling the spatial variability of steel corrosion is very important for the assessment of the remaining service life of corroded structures or time for maintenance. To study the changes of spatial variability of steel weight loss over time, a continuous monitoring is necessary. In this paper, a novel procedure of X-ray technique application in monitoring the spatial growth of a corroded bar in a RC specimen is demonstrated along with the digital image processing of X-ray images to estimate the steel weight loss. The relationship of steel weight loss and corrosion cracking is studied at different stages of corrosion. The validity of the estimation method of steel weight loss is also presented.

Deterioration of RC members due to chloride-induced corrosion of reinforcing bars is a common problem in marine environment. After surface crack initiates, RC structures are prone to the occurrence of longitudinal surface cracks and concrete spalling. These deterioration mechanisms adversely cause significant reduction of the service life and performance of RC members. Therefore, it is important to create models to reliably predict the long-term performance of deteriorated RC structures. However, the very limited amount of experimental data on spatial variation of steel weight loss in relation to propagation of surface cracking widths has been reported to create difficulty in improving the degree of accuracy associated with the prediction models. This paper is aimed to experimentally investigate the non-uniform distribution of steel weight loss along reinforcing bars inside RC means by means of X-ray radiography and its correlation with longitudinal crack widths.