Strategic reinforcement for controlling volume-change cracking in base-restrained concrete walls

In this work the control of volume-change cracking in concrete walls with continuous base restrains was considered. Investigators and design codes have proposed several different procedures for the calculation of the amount and distribution of steel reinforcement required for the control of this type of cracking. All these methods provide amounts of reinforcement which are in excess to that really required. This is either due to simplifying the design procedure or neglecting the effect of variable restraint in the wall. Since crack formation and its width depends on the amount of total restrained movement in th concrete member, steel reinforcement is necessary only in positions in which wide cracks are expected to form. Using finite-element analysis to obtain the distribution of restraint in the wall, degree-of-restraint contour diagrams in walls with different length/height ratios of 1, 2, 3, 4, 6 and 8 were prepared. These diagrams can be used to determine the amount and distribution of steel reinsforcement in positions in which it is really effective in controlling cracking. At positions of low restraint in the walls in which no or only narrow cracks will form, only minimum reinforcement will be provided.     

Factors influencing chloride-induced corrosion of reinforcement in concrete

The paper presents the results of a corrosion investigation on rebar electrodes embedded in concrete prism specimens which were exposed to cycles of sea-water spray for up to about 600 days (1200 marine cycles). The w/c ratio of the matrix was varied between 0.45 and 0.76 and the cement content ranged between 330 and 530 kg m^?3. Corrosion potential and polarization resistance of the electrodes were monitored at regular intervals by means of electrochemical procedures using a potentiostat apparatus. The Cl^? and OH^? concentrations in the matrix were also determined at the level of rebar electrodes. The results show that cement content has an insignificant influence on rebar corrosion, w/c ratio being the dominant factor which controls corrosion. The Cl^? and OH^? concentrations of the pore fluid are of secondary importance relative to w/c ratio. Acceptable corrosion rates are achieved at a w/c of 0.45, with the pore fluid Cl^?/OH^? ratio reaching a value of 11.     

Concrete cover cracking due to uniform reinforcement corrosion

Service life design (SLD) is an important tool for civil engineers to ensure that the structural integrity and functionality of the structure is not compromised within a given time frame, i.e. the service life. In SLD of reinforced concrete structures, reinforcement corrosion is of major concern and reinforcement de-passivation is a frequently used limit state. The present paper investigates an alternative limit state: corrosion-induced cover cracking. Results from numerical simulations of concrete cover cracking due to reinforcement corrosion are presented. The potential additional service life is calculated using literature data on corrosion rate and Faraday’s law. The parameters varied comprise reinforcement diameter, concrete cover thickness and concrete material properties, viz. concrete tensile strength and ductility (plain concrete and fibre reinforced concrete). Results obtained from the numerical simulations reveal that, depending on the serviceability limit state applied, the service life of a reinforced concrete structure can be increased significantly by allowing minor damage of the cover.     

Effects of reinforcement configuration and sustained load on the behaviour of reinforced concrete beams affected by reinforcing steel corrosion

Corrosion of reinforcing steel bars in concrete is one of the main causes of early deterioration and reduction of service life of reinforced concrete (RC) structures. This paper reports on the results of an experimental programme that was carried out to study the effect of reinforcement corrosion on the serviceability behaviour of RC beams under load. The main parameters investigated were the effects of reinforcement arrangement and the magnitude of the sustained load. Four series of scaled beams were tested, each series containing six beams, three of which were subjected to reinforcement corrosion while the other three were used as un-corroded control beams. All these beams carried the same sustained load during the process of reinforcement corrosion. The reinforcement arrangement for the fourth test series was identical to the first series but these beams carried a higher sustained test load. All the beams were subjected to a four-point bending load arrangement. Corrosion of the tension reinforcement was accelerated using an impressed current while the soffits of the beams were immersed in a 3% sodium chloride solution. The evolution of reinforcement corrosion and central deflection under simultaneous load and corrosion is given. The deflections of the beams increase with progressive corrosion of the reinforcement especially during the early stages of corrosion as a result of propagation of transverse cracks and the expansive stresses induced by the corrosion products. The importance of the arrangement of the steel in the section of concrete on the performance in terms of deflection was also clarified.     

Effects of reinforcement configuration and sustained load on the behaviour of reinforced concrete beams affected by reinforcing steel corrosion

Corrosion of reinforcing steel bars in concrete is one of the main causes of early deterioration and reduction of service life of reinforced concrete (RC) structures. This paper reports on the results of an experimental programme that was carried out to study the effect of reinforcement corrosion on the serviceability behaviour of RC beams under load. The main parameters investigated were the effects of reinforcement arrangement and the magnitude of the sustained load. Four series of scaled beams were tested, each series containing six beams, three of which were subjected to reinforcement corrosion while the other three were used as un-corroded control beams. All these beams carried the same sustained load during the process of reinforcement corrosion. The reinforcement arrangement for the fourth test series was identical to the first series but these beams carried a higher sustained test load. All the beams were subjected to a four-point bending load arrangement. Corrosion of the tension reinforcement was accelerated using an impressed current while the soffits of the beams were immersed in a 3% sodium chloride solution. The evolution of reinforcement corrosion and central deflection under simultaneous load and corrosion is given. The deflections of the beams increase with progressive corrosion of the reinforcement especially during the early stages of corrosion as a result of propagation of transverse cracks and the expansive stresses induced by the corrosion products. The importance of the arrangement of the steel in the section of concrete on the performance in terms of deflection was also clarified.     

Examples of reinforcement corrosion monitoring by embedded sensors in concrete structures

An increasing number of concrete structures are being monitored to enhance their durability. However, the literature provides only some guidance for the interpretation of the monitoring results [Broomfield JP. Corrosion of steel in concrete, understanding investigation and repair. 2nd ed. UK: Taylor & Francis; 2006; Andrade C, Alonso C. On-site measurements of corrosion rate of reinforcements. Constr Build Mater 2001;15(2–3):141–45; EN 206 2000. Concrete—Part 1: specification, performance, production and conformity]. Past experience shows the difficulty of interpreting the data collected due to the influence of temperature and moisture, and of using these data to predict future evolution of any deterioration processes.This paper presents several examples of recorded data for corrosion potential, electrical resistance and corrosion rates, along with a methodology to obtain a representative corrosion rate, averaged per year. The representative value can be used in corrosion predictive models to calculate the remaining service life.     

Thermally induced softening and cracking in concrete with minimal reinforcement

This paper deals with modeling of softening and cracking induced by non-uniform cooling or shrinkage of reinforced concrete. Concrete and reinforcement are described by a set of constitutive equations and cooling is assumed to be a linear thermal diffusion process. The investigated structure is a medium-thick wall with external restraint modeled by springs. The main purpose of the paper is to study the role and the amount of the socalled minimum reinforcement necessary to control cracking. Another purpose is to find the force actually arising in the wall during cooling and also to compute the range of softening and cracking of the concrete. Sensitivity of the results is studied in a parametric investigation.     

Meso-scale numerical investigation on cracking of cover concrete induced by corrosion of reinforcing steel

Concrete cover cracking induced by corrosion of steel reinforcement is a major influencing factor for durability and serviceability of reinforced concrete structures. Here in this study, the influence of concrete meso-structure on the failure pattern of concrete cover is accounted for. The concrete is assumed to be a three-phase composite composed of aggregate, mortar matrix and the interfacial transition zone (ITZ). And a concrete random aggregate structure is established for the study on the mechanical behavior of radial corrosion expansion. In the present simulations, the plasticity damaged model is used to describe the mechanical behavior of the mortar matrix and the ITZ, and it is assumed that the corrosion of steel reinforcement is uniform. The cracking of concrete cover due to steel reinforcement corrosion is numerically simulated. The simulation results have a good agreement with the available test data and they are between the two analytical results. The failure patterns obtained from the macro-scale homogeneous model and the meso-scale heterogeneous model are compared. Furthermore, the influences of ratio of cover thickness and reinforcement diameter (i.e. c/d), the location of the steel reinforcement (i.e., placed at the middle and corner zones) and the concrete tensile strength on the steel corrosion rate when the concrete cover cracks are investigated. Finally, some useful conclusions are drawn.     

Investigation on the cracking behavior of concrete cover induced by corner located rebar corrosion

Non-uniform corrosion of reinforcement causes concrete cracking in chloride contaminated RC structures. Due to the special boundary conditions, the concrete cover with corner located rebar is often subjected to the attack of chloride ions in a marine environment from two directions, and thus the corresponding non-uniform corrosion distribution should be different from the one for side-located rebar. The aim of the work is to explore the effect of corner located rebar corrosion on the cracking of cover concrete. For corner located rebar, an improved non-uniform corrosion distribution model was established based on the analysis results of two-dimensional chloride diffusion in concrete. Considering the heterogeneities of concrete, a meso-scale mechanical model and method for the study on the failure behavior of concrete cover was built. In the analysis model and method, the non-uniform radial displacement distribution was adopted to simulate the corrosion expansion behavior of the rebar. The cracking of concrete cover with corner located rebar was simulated and studied. The present approach was verified by the available experimental observations. The influences of concrete heterogeneity, corrosion distribution types, rebar diameter and concrete cover thickness on the failure patterns of concrete cover and the expansive pressure were investigated. The simulation results indicate that the developed approach can well describe the cracking behavior of cover concrete and the corrosion-expansion behavior of steel rebar.     

Lattice modelling of corrosion induced cracking and bond in reinforced concrete

A lattice approach is used to describe the mechanical interaction of a corroding reinforcement bar, the surrounding concrete and the interface between steel reinforcement and concrete. The cross-section of the ribbed reinforcement bar is taken to be circular, assuming that the interaction of the ribs and the surrounding concrete can be captured by a cap-plasticity interface model. The expansive corrosion process is represented by an Eigenstrain in the lattice elements forming the interface between concrete and reinforcement. Several pull-out tests with varying degree of corrosion are analysed. The numerical results are compared with experiments reported in the literature. The influence of the properties of concrete are studied. The proposed lattice approach offers insight into corrosion induced cracking and its influence on bond strength.     

基于XFEM的强震区砼重力坝开裂与配筋抗震措施研究

已有震害表明,混凝土坝遭遇强烈地震将不可避免地产生开裂。扩展有限元法（XFEM）通过在相关节点的影响域上富集非连续位移模式,使得对非连续位移场的表征独立于单元边界,可以有效描述混凝土中的裂纹扩展。基于扩展有限元模型,采用合理的地震波动模型对国内某混凝土重力坝强震下的动力破坏过程进行了分析;针对大坝破坏情况,应用嵌入式滑移模型模拟了混凝土重力坝配筋前后的地震响应和破坏状况,据此评价局部配筋的抗震效果。研究表明,局部配置抗震钢筋虽无法防止裂缝的发生,但可有效限制坝体裂缝的开裂扩展范围及深度,减少裂缝的开度,有效改善坝体的抗震性能。     

The influence of corrosion on bond properties between concrete and reinforcement in concrete structures

The rebar corrosion in reinforced concrete is one of the most extensive pathologies affecting the performance of concrete structures. Chloride-induced rebar corrosion damage results mainly from the use of de-icing salts in cold climates and/or exposure to marine environments. Carbonation damage is a further important degradation mechanism. The internal consequences of corrosion are the modification of the steel behavior and degradation of the steel–concrete bond. This work is devoted to the influence of the controlled corrosion on the adherence between steel and concrete. A new geometry of specimen has been designed to: (i) avoid the lateral confining stresses that appear during the classical pullout tests and (ii) permit to impose a known confinement for the study of its influence on the behavior of the interface. Five specimens with different levels of corrosion have been tested in this contribution. Reinforcing bars embedded in concrete were submitted to accelerated corrosion using an external current source. The magnitude of corrosion was measured using both Faraday’s law and the weight loss method. The level of corrosion varied from 0% to 0.76%. The geometry of the specimens allowed us to take series of digital pictures during the tests, which were analyzed using a digital image correlation, the procedure named CORRELI^LMT. The results of pullout tests proposed in this contribution indicate that: (i) levels of corrosion that are less than 0.4% of weight loss improves the bond stress and (ii) levels of corrosion resulting in more than 0.4% of weight loss lead to a reduction of the bond stress value.     

Inhibitor protection of a reinforcement steel strengthened by heat treatment against the corrosion cracking in chloride media

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 3, pp. 104–107, May–June, 1988.     

Modeling damage in concrete caused by corrosion of reinforcement: coupled 3D FE model

Reinforced concrete structures, which are exposed to aggressive environmental conditions, such as structures close to the sea or highway bridges and garages exposed to de-icing salts, often exhibit damage due to corrosion. Damage is usually manifested in the form of cracking and spalling of concrete cover caused by expansion of corrosion products around reinforcement. The reparation of corroded structure is related with relatively high direct and indirect costs. Therefore, it is of great importance to have a model, which is able to realistically predict influence of corrosion on the safety and durability of reinforced concrete structures. In the present contribution a 3D chemo-hygro-thermo-mechanical model for concrete is presented. In the model the interaction between non-mechanical influences (distribution of temperature, humidity, oxygen, chloride and rust) and mechanical properties of concrete (damage), is accounted for. The mechanical part of the model is based on the microplane model. It has recently been shown that the model is able to realistically describe the processes before and after depassivation of reinforcement and that it correctly accounts for the interaction between mechanical (damage) and non-mechanical processes in concrete. In the present paper application of the model is illustrated on two numerical examples. The first demonstrates the influence of expansion of corrosion products on damage of the beam specimen in cases with and without accounting for the transport of rust through cracks. It is shown that the transport of corrosion products through cracks can significantly influence the corrosion induced damage. In the second example the numerically predicted crack patterns due to corrosion of reinforcement in a beam are compared with experimental results. The influence of the anode?Ccathode regions on the corrosion induced damage is investigated. The comparison between numerical results and experimental evidence shows that the model is able to realistically predict experimentally observed crack pattern and that the position of anode and cathode strongly influences the crack pattern and corrosion rate.     

Laboratory studies on influence of transverse cracking on chloride-induced corrosion rate in concrete

To clarify the corrosion mechanism of steel induced by transverse crack, a study on the influence of crack widths and epoxy coating on corrosion of steel bars in cracked concrete is presented here. Microcell and macrocell corrosions of bars were investigated on single crack specimens with crack widths of 0.08, 0.26, 0.38 and 0.94 mm. The entire study was carried out in an artificially created chloride ion-induced corrosion environment. The results show that the steel in cracks was activated once the transverse crack occurred on concrete element, and the macrocell corrosion must co-exist with microcell corrosion of reinforcements in test specimens with transverse crack. The macrocell current of steel elements were separated from the crack width, and the wider the transverse crack is, the higher corroded area and the greater microcell current of the rebar is. Oxygen and water go into concrete through crack instead of through concrete cover. The epoxy coating cannot prevent the occurrence and propagation of crack, so it was not effective to prevent corrosion of steel bars in cracked concrete.     

The rate of corrosion of concrete reinforcement and possibilities of its mathematical modelling

The paper describes a method for the mathematical modelling of steel reinforcement corrosion rate. This method is based exclusively on experimental results and expression of the influence of significant corrosion factors in the form of functional relations. The method takes into account the reality of the effects of corrosion factors, their contigency and complexity, and various circumstances occurring in practice. It represents one way towards the development of methods for the prediction of service life of reinforced concrete and structures.