Effect of corrosion on the bond between steel and concrete: an overview

The volume increase that takes place when reinforcement in concrete corrodes causes splitting stresses in the concrete. Thereby, the bond between the reinforcement and the concrete is influenced. This effect has been studied both experimentally and theoretically by many researchers. In the current paper, the effect of corrosion on the bond between reinforcement and concrete is investigated and described in a systematic way. Literature studies of experimental work are combined with finite element analyses of different cases. In this way, modelling is used as a tool to give the basic understanding, and the results are compared with experiments. An overview of the effect depending on the reinforcement type, existence of transverse reinforcement and confinement owing to concrete and boundaries is given. This overview is intended to be of help in understanding the phenomena as well as in assessment of existing structures

Lap splice over a grouted joint in a lattice girder system

Load-carrying in two directions in lattice girder slab systems by complementing with lapped reinforcement across the joints at the construction site was studied. A detailing of load-carrying joints without any reinforcement across the cast joint was considered. The behaviour of the cast joint between the precast concrete and the in situ cast concrete is very important. Two different surface treatments were tested in two types of detail tests of the cast joint: one type in which the cast joint was loaded in shear, and one in tension. Furthermore, the detailing of the joint between two precast concrete panels was tested in bending in full-scale tests. The detail tests were used to calibrate a friction model of the cast joint, which was then used in finite-element analyses (FEAs) of the full-scale tests. In the full-scale tests, the joints were strong enough to carry the applied load; thus, the failure mode was rupture of the reinforcement in all full-scale tests, and only one crack occurred—in the in situ cast concrete above the joint between the precast elements. However, the FEAs of the full-scale tests revealed that the detailing was sensitive to secondary cracking

Modelling of bond between three-wire strands and concrete

The bond between strands and concrete is of importance for prestressed concrete. The research presented in the current paper aims at a better understanding of the bond mechanism, and of how different detailings of the strand interface affect the behaviour. A bond model for three-wire strands was established and calibrated by use of pull-through tests. The results from finite element (FE) analyses with the bond model and the tests were used in parallel. It was found that adhesion, friction and the ability to develop normal stresses determine the bond response of the strand; consequently, they were used as input parameters in the bond model. How different detailing of the strand surface affects these parameters, and the influence on the bond mechanism, are shown. For example, adhesion has the strongest influence on the initial bond response in the cases of smooth and indented strands. Regarding indented strands, the maximum bond capacity is determined by the strand indentation. The knowledge gained can be used to design the strands for a certain bond behaviour. \ua9 2006 Thomas Telford Ltd

The baby-boom is over and the ageing shock awaits: populist media imagery in news-press representations of population ageing

From an international perspective, media representations of population ageing have been described as apocalyptic in character. In this article, we analyse the way population ageing is represented in three Swedish newspapers: Aftonbladet, Dagens Nyheter and Va¨sterbottens-Kuriren. The aim is to investigate Swedish news-press representations of population ageing and the old age identities that they offer. We conduct qualitative analyses of the articulations between the verbal content and the use of illustrations, metaphorical language, headlines and captions using the concepts offered by discourse theory. The analysis of the material shows that the studied newspapers firmly position population ageing within a wider discourse of political economy and as a threat to the concept of welfare. Growth is promoted as a self-evident means for adjusting to the expected threat. Illustrations and metaphorical language helped to constitute population ageing as a serious, dichotomised (e.g. young vs. old) and emotive (e.g. addressing anxiety and ear) problem. The analyses also show how the representations of population ageing bear some populist features, and we argue that such features support a de-politicisation of the phenomenon population ageing

Nonlinear analysis of crack widths in reinforced concrete

Former research indicates that the crack width close to the bar can be a better indicator for the risk for reinforcement corrosion than, as current concrete codes impose, the crack width at the concrete surface. In this paper a finite-element model is used to increase the understanding of how the crack width varies at different levels from the reinforcement and how different mechanisms control this behaviour. Concrete and reinforcement are modelled with solid elements, where nonlinear fracture mechanics is used for the concrete material and a model, which has been modified for this purpose, describes the bond between steel and concrete. The results of the finite-element calculations of the crack widths are compared to earlier experimental studies. Both the finite-element analysis and experimental studies are performed on axially loaded concrete prisms with a central 16 mm reinforcement bar and concrete covers of 30, 50 and 70 mm. The finite-element analysis verifies the results from former experimental research, where the crack widths close to the reinforcement bar are affected only slightly, or not at all, by the concrete cover. This can lead to new possibilities of enlarging the concrete cover and increasing the durability of concrete structures in future

Experiments and calibration of a bond-slip relation and efficiency factors for textile reinforcement in concrete

Textile reinforcement yarns consist of many filaments, which can slip relative each other. At modelling of the global structural behaviour, interfilament slip in the yarns, and slip between the yarns and the concrete can be considered by efficiency factors for the stiffness and strength of the yarns, and by applying a bond-slip relation between yarns and concrete. In this work, an effective and robust method for calibration of such models was developed. Two-sided asymmetrical pull-out tests were carried out, with varying embedment lengths designed to obtain both pull-out and rupture of the textile as failure mode. The efficiency factors for strength and stiffness of the textile were very similar, 34% and 35% respectively. This indicates the stress distribution within a yarn to be uneven in a similar manner for small and large stress levels, and that interfilament slip has a larger influence than variation of filaments’ strength

Incorporation of pre-existing longitudinal cracks in finite element analyses of corroded reinforced concrete beams failing in anchorage

Transportation infrastructure is of fundamental importance and must be regularly assessed to ensure its safety and serviceability. The assessment of ageing reinforced concrete bridge stock may need to consider corrosion and cracks, as the likelihood of deterioration increases with age. This work accordingly investigates the incorporation of pre-existing anchorage zone corrosion cracks into the finite element modelling of reinforced concrete beam structural behaviour. Three methods of accounting for cracks were applied: (1) modifying the bond stress–slip relation, (2) weakening elements at the position of the crack, and (3) weakened discrete crack elements. The results show that modifying the bond stress–slip relation results in accurate predictions of the ultimate capacity when one-dimensional reinforcement bars are used in the model. Weakening elements at the position of the crack provides reasonable results when the anchorage is modelled with three-dimensional reinforcement bars and a frictional bond model. The implementation of discrete cracks was found to be unsuitable for the studied load situation, as compressive stresses formed perpendicular to the crack. It was concluded that the capacity of the studied case could be well estimated based on visual measurements, without knowledge of the exact corrosion level

Corrosion of naturally corroded, plain reinforcing bars

Reinforced Concrete is known to be susceptible to corrosion damages. Corrosion, by reducing strength and ductility of the reinforcing bar and modifying the steel/concrete interface, hinders the overall safety of the structure. This work investigates the bond of naturally corroded, plain reinforcing bars. Specimens were taken from an 80-year-old bridge and tested using pull-out and 3-point bending tests. Additionally , neutron and X-ray tomography is used to observe the distribution of corrosion products. Results highlight the influence of casting position on the bond of plain bars. Specifically, the distribution of corrosion products is influenced by the bleeding zone underneath top-cast bars. Corrosion products are shown to deposit in macro-pores and to adhere to the bar

Monitoring corrosion-induced concrete cracking adjacent to the steel-concrete interface

Substantial research effort has been devoted on linking corrosion-induced cracking of concrete with the internal corrosion damage level. Still, numerical models of the corrosion and cracking process require internal parameters, that cannot be directly evaluated from experimental data. Therefore, this study provides a novel experimental method for monitoring the effects of steel corrosion adjacent to the steel-concrete interface. This non-destructive method is suited for small-scale laboratory-made specimen, and was designed to provide missing information required for subsequent calibration of numerical models. Hollow steel bars were cast into concrete and subjected to accelerated corrosion using the impressed current technique. The deformations of the hollow steel bars were measured using distributed strain sensing in an optical fibre, attached to the inner surface of the hollow steel bars. After the corrosion period, X-ray Computed Tomography scans were performed to evaluate concrete cracking and corrosion level. The results reveal a non-uniform distribution of strain around the perimeter of the steel, indicating a non-uniform radial stress distribution. The non-uniformity correlated very well with the position of the corrosion-induced cracks; with extension hoop strains in the steel at the location of these cracks and contraction hoop strains in between. Further, the corrosion level varied around the perimeter, with higher values near cracks. The combination of non-destructive monitoring techniques used in this study on small-scale laboratory-made specimens show great potential to reveal new insights on how the corrosion pattern, corrosion-induced cracking of the concrete cover and stress (indirectly measured through the strain in the steel) interact throughout the corrosion process