Modeling of corrosion-induced cracking is limited by lacking knowledge on the behavior of corrosion products. In this work, the corrosion and cracking processes were experimentally investigated in 3D at two different stages. The processes were measured at micro-structural scale, applying nondestructive neutron and X-ray computed tomography in two scans at different stages in the corrosion process. A method to evaluate the average volumetric strain of the compressed corrosion layer was proposed and displacements in the concrete matrix were measured. Strain localization revealed cracks not directly visible in the images. Multimodal tomography demonstrated to be an effective method for investigating steel corrosion in reinforced concrete.

Modeling of corrosion-induced cracking is limited by lacking knowledge on the behavior of corrosion products. In this work, the corrosion and cracking processes were experimentally investigated in 4D (three spatial dimensions + time). The processes were monitored at micro-structural scale, applying nondestructive neutron and X-ray computed tomography in multiple scans at different stages in the corrosion process. A method to evaluate the average volumetric strain of the compressed corrosion layer was proposed. Further, displacements in the concrete matrix were captured with subvoxel sensitivity. Strain localization revealed cracks smaller than direct visible in the image data.

This study undertaken on a nine-year-old cracked concrete panel further investigates the impact of cracks on the corrosion performance of conventional steel reinforcement in marine-exposed concrete to explain observed monitoring data. The present data covers seven 1.80 m long (12.6 m) reinforcing bars embedded in good quality concrete (w/b = 0.40 and cover >75 mm). Each bar was crossed by two horizontal cracks (surface crack widths 0.20-0.30 mm). The investigation showed no corrosion on the surface of the reinforcing bars, in either cracked or uncracked areas. Two of the seven reinforcing bars were instrumented in the vicinity of the cracks. Extensive corrosion was found in the interior of all instrumented parts of these bars. This may explain the monitoring data despite the lack of corrosion on the exterior surface of the two instrumented rebars. However, with no other weaknesses, the remaining conventional rebars showed no impact from the cracks.

Surface crack width is regulated in codes to limit corrosion of reinforcement bars in concrete. However, the influence of surface crack width on corrosion damages is not directly inferable from previous research.In this work, data on corroded cracked concrete specimens in chloride environments was compiled. Detailed information was included, such as crack and pit locations, local corrosion pattern, etc. Five hypotheses on the influence of transversal cracks on corrosion damage were formulated, and statistical methods were used to test them on the dataset.Transversal cracks were good indicators of the position of corrosion pits. The corrosion rate of the pit increased in proximity of a crack. With time, pits grew in depth at a slower rate but increased in number. No clear correlation between surface crack width and corrosion damage was found. Results point out discrepancies in the collected data, arguing for the need of well-defined procedures for assessing crack and corrosion damage.Further, the statistical treatment allowed for identification of bias in existing data, which was used as a research planning tool to provide guidance on the design of additional experiments. Thus, recommendations for future experimental work required to reduce the bias are given.

Surface crack width is regulated in codes to limit corrosion of reinforcement bars in concrete. However, the influence of surface crack width on corrosion damages is not directly inferable from previous research.In this work, a compilation of data from literature is presented, based on recorded data on corroded cracked concrete specimens in chloride environments. Five hypotheses on the influence of transversal cracks on corrosion damage were formulated, and statistical methods were used to test them on the dataset. Transversal cracks were good indicators of the position of corrosion pits. The corrosion rate of the pit increased in proximity of a crack. With time, pits grew in depth at a slower rate but increased in number. No clear correlation between surface crack width and corrosion damage was found. Results point out discrepancies in the collected data, arguing for the need of well-defined procedures for assessing crack openings and corrosion damage.

Corrosion of reinforcing bars constitutes the largest threat to the durability of concrete structures. Thus, several studies have investigated the nature of the corrosion products, most using post-mortem analyses. However, corrosion products evolve when in contact with oxygen, hindering result interpretation. This work presents instead a state-of-the-art, non-destructive 3D method for the assessment of corrosion of embedded reinforcements. Multimodal neutron and X-ray tomography was used to observe, non-destructively, the characteristics of the corrosion products in two concrete samples, with the aim of investigating possible benefits of the use of this technique for reinforced concrete structures. One sample was naturally corroded, extracted from an 81-year-old bridge, the other was corroded via the galvanostatic method, resulting in corrosion-induced cracks. Quantitative and qualitative data was acquired, including the iron-to-rust volumetric ratio in macroscopic interfacial voids and the thickness of the corrosion layer at the steel concrete interface. The iron-to-rust volumetric ratio corresponded to large, soluble, corrosion products, forming in environments with low availability of oxygen for both samples.

Reinforced Concrete (RC) heritage structures are often affected by corrosion. Consequently, knowledge about the effect of corrosion on the bond between reinforcing bars and surrounding concrete is critical when assessing the structural performance of these structures. In earlier work, structural tests were carried out on segments of edge beams taken from a decommissioned RC bridge. The specimens had naturally corroded plain reinforcement bars and three-point bending tests were conducted, to investigate their anchorage capacity. In this study, non-linear finite element analyses (NLFEA) were carried out to gain further insight into the bond behaviour of the tested specimens, including the effect of corrosion on the bond-slip relationship. Two different, one-dimensional (1D), bond-slip relationships were calibrated for each tested bar, to account for loss of bond upon yielding. The calibration process was based on a comparison between significant numerical and experimental results, including load-deflection curve, crack pattern and asymmetrical distribution of the yield penetration along the length of the bar. Good agreement between the FE analyses and experimental tests was observed. Finally, the calibrated bond-slip relationships for nine beams with different corrosion levels, casting positions, and visual damage are presented and discussed. The loss of bond at yielding and yield penetration asymmetry are both shown to be crucial factors for adequately describing structural behaviour.

Reinforced Concrete (RC) is the most common construction material in existing structures. However, RC structures are susceptible to deterioration over time, with corrosion of the reinforcing steel as most common mechanism. Corrosion reduces strength and ductility provided by the reinforcement bars and affects their interaction with the concrete. Research on the structural effects of corrosion commonly focuses on deformed bars and applies artificial corrosion. Performance is evaluated based on testing the bond between the bars and the concrete. Plain (smooth) reinforcing bars, as typical in older structures, are seldom studied. Plain bars interact differently with concrete, due to the absence of ribs. Additionally, doubts on the relevance of artificial corrosion methods have been raised. Thus, there is a lack of knowledge on the effects of corrosion of plain bars, and naturally corroded specimens are the ideal mean of acquiring it. This work investigates the bond of naturally corroded, plain reinforcement bars by testing specimens taken from the edge beams of a decommissioned, 80-year-old bridge. Pilot tests were performed to investigate possible test configurations, to which a total of 20 beams were subjected to displacement-controlled 3-point bending. The beams presented different levels of damage, and the corrosion level of each tensile reinforcement bar was afterwards measured using of a 3D scanner. All but three of the tested specimens were able to anchor the yield force of the bars after the opening of one or two major bending cracks in the middle. Bending failure, not bond strength, limited the load-carrying capacity for the majority of test specimens. At large deflections, end-slip of the reinforcement bars was observed; thus, anchorage limited the deformation capacity. The average bond strength was evaluated separately in the unyielded and in the yielded zones. The average bond strength in the unyielded zone was found to be equal to 7.4 MPa, with a standard deviation of 3.3 MPa. The casting position was identified as an important factor. Bottom-cast bars had higher bond strength when uncorroded, but were more prone to external cracks in the bond region and consequently loss of bond strength for small corrosion levels. Top-cast bars had lower bond strength when uncorroded, but reached higher bond strength with increasing corrosion levels, due to the absence of external cracks. These differences are likely the result of a higher density of the concrete surrounding the bottom-cast bars. In the yielded zones, substantial loss of bond strength was observed, with an average of 1 MPa. This affected the overall structural behaviour, which was observed to change from beam to arch action for larger deflections. To conclude, the results improve our understanding of the behaviour of older structures with plain bars and will enable, in the long run, improved assessment methods.

In a recent study, corrosion of reinforcement steel within reinforced concrete samples was observed and quantified non-destructively. This is one of the first successful attempts at employing multimodal neutron and X-ray tomography for the identification of corrosion products in reinforced concrete. What makes the use of imaging techniques uniquely powerful in the context of reinforced concrete is their nondestructive nature: the chemical composition of corrosion products rapidly changes when exposed to air, thus making it difficult to assess both their composition and distributions with the more traditional, yet destructive, tests. Additionally, the use of X-rays alone is very detrimentally affected by the high attenuation of the reinforcement bar embedded in the concrete. The distribution of the corrosion products and their expansion coefficients are two fundamental parameters when modeling the corrosion process in concrete structures. Corrosion products occupy a volume larger than the steel they come from, but the ratio between the original steel volume and one of the corrosion products may vary between 2.2 and 6.4 [1], depending on the availability of hydrogen and oxygen. Additionally, the distribution of corrosion products, and their expansion coefficient, is expected to be influenced by the presence of voids and defects in the concrete surrounding the reinforcement bar. It is in this context that neutron imaging, combined with X-ray tomography, proves to be extremely valuable. Since corrosion products are a combination of iron, hydrogen and oxygen, the high absorption coefficient of hydrogen makes neutron imaging an ideal probe to assess the corrosion products in concrete. However, other aspects of the composition of the concrete are harder to capture with neutron imaging alone. A reinforced concrete sample usually comprises steel, cement paste, aggregates, air voids, and corrosion products, when present. Of these, aggregates and pores are hard to distinguish from neutron imaging data alone. Nevertheless, the use of X-rays, to which voids are almost transparent, is pivotal in providing all the information necessary for rigorously segmenting the image, that is, for discerning the individual components of the concrete to assess the interplay between corrosion, porosity and overall sample geometry. Figure 1 shows a cross-sectional view of a reinforced concrete sample, after neutron and X-ray data were aligned and superimposed. The identification of the different phases of the image in Figure 1 allows to quantify the corrosion products in the sample and thus, to estimate the expansion coefficient of the corrosion products. The presented study focuses on two corroded reinforced concrete samples, clearly showing the applicability of multimodal neutron and X-ray tomography for the identification of key metrics for understanding and modeling the corrosion process in reinforced concrete structures.

Reinforced concrete structures are often damaged by corrosion, which affects the interaction between reinforcement bars and concrete. Earlier studies mostly applied artificial corrosion to test the bond between deformed bars and concrete. However, there is a lack of knowledge on the effects of natural corrosion on plain bars. In this paper, 20 beams with naturally corroded plain bars and varying amount of damage were taken from an 80-year-old bridge and tested in three-point bending. All but three of the specimens anchored the yield force of the bars after the opening of one or two major bending cracks. At large deflections, the load-carrying mechanism changed from beam to arch action. Eventually, end-slip of the reinforcement bars was observed. The bars were extracted, cleaned, three-dimensionally scanned, and tested in tension. The average bond strength in the unyielded zone was found to be equal to 7.39 MPa, with a standard deviation of 3.33 MPa. The casting position was identified as an important factor: when uncorroded, bottom-cast bars had a higher bond strength than that of top-cast bars. However, they were more prone to splitting cracks and, consequently, loss of bond strength for small corrosion levels. Top-cast bars had increasing bond strength with increasing corrosion levels, owing to the absence of external cracks. These differences were likely related to a denser concrete surrounding the bottom-cast bars. The remaining bond capacity in the yielded zones was evaluated to be approximately 1.0 MPa.

Mimicking natural deterioration in accelerated tests is challenging; a highly relevant alternative option is to use deteriorated specimens from decommissioned structures. This paper describes a methodology to select and design tests of the bond and anchorage between reinforcement and concrete in such specimens, with the aim of providing general information, needed when developing methods for assessing structures in general. The methodology includes the following steps: (1) choice of existing structure for samples, (2) choice of test method, (3) design of test setup, and (4) design of test programme. Each step is discussed in detail and comments are made on considerations and challenges arising specifically due to the use of specimens from existing structures. As the scatter of test results is typically large, a suitable test method should enable a large number of tests by being robust, quick and affordable. It is recommended to keep track of the position of the specimens in the original structure, to document cracks, and to take samples also of uncorroded bars. These can then be used for reference in quantifying the corrosion level of corroded bars. This methodology is exemplified in the design of three test series on edge beams from two bridges; two series resulted in beam test setups and one in direct pull-out tests. The methodology described strongly highlights that careful investigations are required to design experiments which generate reliable data. Acquiring data from decommissioned structures will improve our understanding of the structural behaviour of existing structures and thus enable improved assessment methods.

Several reliability methods available in literature combined with various modelling approaches are compared in this current work in the context of two experimental reinforced concrete (RC) beams. One beam failed in bending while the other beam failed in shear due to diagonal tension. The structural behaviour is described by analytical models and nonlinear finite element models. The changes in predicted reliability of these structures with increasing loads are evaluated by different reliability methods and the results are compared

Reinforced concrete bridges are common in Sweden and often damaged by reinforcementcorrosion that reduces the safety of the structure. This issue has been addressed in several researchprojects with, however, a strong focus on ribbed bars, while further knowledge about smooth barsis still needed. Edge beams from a bridge in Gullspang with naturally corroded smooth bars willbe studied so as to provide benchmark data for the assessment of the load-carrying capacity ofexisting structures with corroded smooth bars. Structural tests are carried out on several beams,with varying amounts of corrosion damage, measuring anchorage properties such as applied loadand end-slip.

Concrete structures are strongly affected by reinforcement corrosion, the most common cause of deterioration. Most studies on structural effects of corrosion rely on artificial methods to obtain a corrosion level that would otherwise require years, but doubts on the soundness of the methods have been raised. Specimens taken from existing structures offer the chance of studying the effect of natural corrosion, however the choice of the test setup is challenging. Hence, pilot tests are carried out to investigate the optimal design for testing the anchorage capacity of specimens with smooth reinforcements. The outcome is an asymmetrically supported 3-point bending beam test. The benefits of using complementary tools as Digital Image Correlation (DIC), Non-Linear Finite Element Analysis (NLFEA), pull-out tests and tensile tests and 3D scanning of the bars are presented.

Pa Chalmers tekniska hogskola borjade 2017 ett doktorandprojekt som syftar till att forbattra kunskapen om hur betongkonstruktioners barformaga paverkas av aldringsprocesser. I projektet togs provkroppar fran en bro i Gullspang, som byggdes 1934. Bron byggdes med slata armeringsstanger, vilket var vanligt pa 1930-talet. Slata armeringsstanger anvands inte langre i nya konstruktioner, men de ar fortfarande vanligt forekommande i befintliga betongkonstruktioner. Den vanligaste skadetypen i armerade betongkonstruktioner ar armeringskorrosion, vilket var anledningen till att bron i Gullspang revs 2016. Att forsta hur slata armeringsstal med korrosionsskador fungerar ar viktigt for att kunna bedoma aldre konstruktioners barformaga och undvika rivning i onodan. I den har artikeln sammanfattas projektets viktigaste resultat.