Damage analysis and cracking model of reinforced concrete structures with rebar corrosion

The damage of concrete cover in reinforced concrete structures induced by reinforcing steel corrosion is investigated in this study. The damage process of the concrete cover can be divided into two distinct stages: the non-cracking stage and the partial cracking stage. An analytical model based on damage mechanics and elastic mechanics is developed to predict the concrete cracking due to steel corrosion. Based on this model, the expansive pressure and the radial loss of steel bar are discussed. Parametric studies are carried out to examine the effects of the correlative factors on the expansive pressure and the steel loss.     

Electrochemical realkalisation for rehabilitation of reinforced concrete structures

In steel reinforced and prestressed concrete structures depassivation of the reinforcing steel can take place due to carbonation of the concrete cover. Depending on humidity and oxygen availability subsequent corrosion reactions will be initiated. Such conditions require measures to exclude corrosion induced damages during the designed lifetime of the structure. In the last few years an electrochemical realkalisation treatment has been proposed as adequate rehabilitation technique for carbonated concrete. This temporary treatment should increase the pH-value of the concrete pore water solution due to penetration of alkaline electrolyte from the concrete surface as well as repassivate the reinforcement due to electro chemical reactions at the steel surface. In order to clarify the different mechanisms taking place during electrochemical realkalisation laboratory tests have been carried out using carbonated reinforced mortar specimens. The investigations were aimed at checking the influence of various parameters, e.g. treatment time and current density, as well as the efficiency and long-term durability of this rehabilitation method.     

Experimental and probabilistic analysis of time to corrosion-induced cover cracking for marine reinforced concrete structures

Corrosion-induced concrete cover cracking is an important indication of durability limit state for marine reinforced concrete structures. In this paper, two analytical models predicting the time from corrosion initiation to cover cracking and their main differences were introduced. Based on an accelerated corrosion test, two models’ applicability and variability were compared and discussed with experimental data. Considering the random nature of influencing factors, a probabilistic model was developed by using Monte Carlo simulation technique. The results showed that the cracking time could be modelled by the Weibull distribution. Finally, the probability analytical technology was applied to a marine reinforced concrete pier with four different durability design levels. It is found that both the mean and 90% confidence interval of the cracking time increase when the durability design specifications change from low level to extreme level, which indicates that the accurate prediction of cracking time with a deterministic model will become more difficult accordingly.     

Thermodynamic analysis of inclusion in weld

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Cathodic protection of new and old reinforced concrete structures

Current and potential distributions measured on concrete slabs and simulated by computer modelling are discussed in relation with the application of cathodic protection to new reinforced structures as a corrosion preventive method. The results show high penetration of cathodic protection over the depth of uncontaminated concrete, so that even a rebar relatively distant from the anode can be polarized, whereas the penetration is limited to the rebars near to the anode in chloride contaminated slabs with corroding rebars. The great throwing power and the wide range of protection potentials for uncorroding concrete structure enable safe application of the cathodic protection even to new prestressed structures.     

Several questions about electrochemical rehabilitation methods for reinforced concrete structures

Electrochemical realkalisation (ERA) and electrochemical chloride removal (ECR) have shown their capacity to eliminate, in just a few weeks, the causes of corrosion in reinforced concrete structures (RCS), and for this reason are currently receiving very special attention. Nevertheless, the present state of the art has not progressed enough to dissipate doubts about the efficiency of ERA and ECR as electrochemical rehabilitation methods (ERM) for corroding RCS. A series of highly important questions persist, and continue to be cause of controversy among specialists in the construction sector, which can be summed up in one all-encompassing question, namely:

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Is removing the sources of corrosion in RCS sufficient to stop rusting?To obtain a response to this capital question, electrochemical corrosion analysis techniques are used to study the responses of clean and precorroded steel electrodes embedded in small mortar specimens without chloride additions and large mortar slabs with and without chloride contamination. According to the results obtained, ERM are efficient in delaying the start of corrosion if used preventively. However, if applied too late they do not assure the repassivation of rebars with high precorrosion levels and consequently are not useful.

     

Experimental analysis of drilling fiber reinforced composites

In comparison with metals, long-fiber reinforced composites have a layered structure, with different properties throughout their thickness. When drilling such structures, internal defects like delamination occur, caused by the drilling loads and their uneven distribution among the plies. The current experimental analysis is focused towards determining the cutting loads distribution (axial and tangential) along the work-piece thickness and tool radius by analyzing the thrust and torque curves when drilling with 3 different drills carbon-fiber (CFRP) and glass-fiber (GFRP) reinforced composite plates. A wide range of cutting parameters is tested. The highest loads are found at the tool tip in the vicinity of the chisel edge for all cases. It is also found that the maximum load per ply varies mainly with the axial feed rate and tool geometry, while the spindle speed has little or no influence. The analysis is useful for selecting the cutting parameters for delamination free drilling and also for conducting drill geometry optimizations.     

Application of radar technology to reinforced concrete structures: a case study

The radar technology, used to perform investigations on the civil buildings, derives from that used for investigations of the ground known with the name of Georadar. This is diffusing rapidly among the investigation methodology not destructive in the field of the structural engineering. It is based on the sending of electromagnetic waves of very short length and the recording of the time of arrival and of the breadth of any signals reflected on the interface between materials with a different dielectric constant. The aim of this paper is to present the operating methodologies and the results achieved by the application in the field of radar methodologies to map utilities, and for applications to civil building with special regard to the determination of the intern morphology, to the lack of homogeneity research and defectiveness and to the determination of the location of the steel reinforcements.Specifically, the system used, made up of one apparatus of field acquisition and another of delayed processing, seems to be able to provide good planimetric and three-dimensional restitution with regard to location and placement. In this paper, special attention has been paid to the processing of the acquired data and on the interpretation of experimental tests conducted on a civil building.     

Electrochemical rehabilitation methods for reinforced concrete structures: advantages and pitfalls

Abstract

There are still many unresolved issues concerning the efficiency of electrochemical realkalisation and electrochemical chloride removal as electrochemical rehabilitation methods for corroding reinforced concrete structures. The present paper seeks to answer a number of questions which, though seemingly elementary, continue to arouse controversy in scientific, technical and economic communities, despite the vast amount of work that has been devoted to research on corrosion in concrete embedded steel, such as whether corrosion can be stopped once it has started, whether corroded reinforced concrete structures can be repassivated, and whether it is sufficient to remove the sources of corrosion in order to stop rusting. A discussion is conducted on the relationship between the prerusting grade of rebars and the possibility of their repassivation; on whether electrochemical rehabilitation methods treatments are efficient, and if so, when and on whether a simple potential measurement can determine the passive or active state of a rebar. For this purpose an analysis is made, using electrochemical, gravimetric and metallographic techniques, of the response of clean and previously corroded steel electrodes in a Ca(OH)₂ saturated solution with and without a sodium nitrite corrosion inhibitor and in cement mortar. The effectiveness of electrochemical realkalisation and electrochemical chloride removal for repassivating prerusted steel in concrete is found to depend heavily on the prerusting grade.     

Mechanical properties of an iron oxide formed by corrosion in reinforced concrete structures

The paper deals with elastic properties of iron oxides formed in reinforced concrete structures. Due to the difficulty to perform mechanical tests on the real oxides presented in the form of (multiple) laminated stratums, the elastic modulus of iron oxides remains unknown. Young’s moduli of porous compact “synthetic oxides” in powder form, obtained in laboratory conditions, were measured from both acoustic measurements and oedometric tests. The elastic modulus of the compact polycrystalline iron oxide is deduced with respect to two models, a micromechanical one and a Hertz’ theory. The full method is validated on a well-known material, the alumina.     

含有纳米级夹杂物的滚动体的应力分析

在滚动轴承工作状态下,滚动接触过程中通常会遇到滚动体内表面含有纳米级夹杂物的情况,纳米级夹杂物会影响滚动体的疲劳寿命。利用TLP3接触疲劳试验机对滚动体的疲劳寿命进行研究,发现纳米级夹杂物是滚动体疲劳寿命的主要影响因素,并基于此问题进行有限元仿真验证。以2μm夹杂物为模型,突破性地实现了网格局部极细划分,网格最小为0.125μm。以有限元软件Abaqus为基础,对滚动接触过程中滚动体以及纳米级夹杂物周围进行应力分析。研究发现,在夹杂物处应力集中,最大等效应力为1634 MPa。     

On the effectiveness of realkalisation as a rehabilitation method for corroded reinforced concrete structures

Based on available experience with the use of electrochemical realkalisation (ERA), a fairly recent method for rehabilitating reinforced concrete structures (RCS), carbonated concrete can undoubtedly be realkalised. To the authors' minds, however, the following questions remain unanswered: (a) does ERA always effectively repassivates reinforcements?; (b) can ERA be considered an end or just a means to ensuring RCS durability?; and (c) what is the use of ERA if it cannot stop corrosion? This work was aimed at answering the previous, controversial questions. To this aim, the behaviour in a Ca(OH)₂ saturated solution, and in a sound uncarbonated mortar consisting of 1:3:0.5 cement, sand and water, of reinforcing bars from an RCS that failed through carbonation after 29 years of service life was examined.     

Development of corrosion sensors for monitoring steel‐corroding agents in reinforced concrete structures

Corrosion sensors were devised to develop a system whereby the depth of chloride permeation from concrete surfaces can be monitored non‐destructively on a real‐time basis using such sensors embedded in cover concrete of reinforced concrete structures. The proposed corrosion sensors were subjected to accelerated corrosion in NaCl solutions, mortar specimens intrinsically containing chlorides, and mortar specimens impregnated with chloride solutions, while recording the changes in the resistance readings. The resistance of sensors increased as the degree of corrosion increased. The time to the first change in the resistance decreased and the corrosion degree and resistance increased as the chloride concentration increased and as the distance from mortar surfaces decreased. It was therefore confirmed that the corrosion sensors are capable of monitoring the depth of chloride permeation with sufficient accuracy.     

The 3-D analysis of discontinuously reinforced aluminum composite microstructures

Automated serial sectioning is presented as an attractive experimental technique for producing an accurate, large-scale three-dimensional (3-D) digital microstructural model of an extruded discontinuously reinforced aluminum composite material. The model is used as input for an elastic-plastic 3-D finite-element analysis that simulates tensile loading of the microstructure. The 3-D visualization and characterization of the resultant deformation structures within the composite microstructure has allowed some of the critical microstructural features that control the tensile response to be identified.     

Development of a new combined corrosion protection system for chloride‐contaminated reinforced concrete structures

Chloride‐induced damage of reinforcing steel is especially for parking garages and bridges often very severe as large amounts of chlorides act on horizontal surfaces which could lead to fast ingress of these detrimental ions up to the level of the reinforcement and subsequently to high rates of corrosion. In order to avoid the disadvantages of conventional rehabilitation (unreliable prognosis with patch repair or high costs and regular maintenance with cathodic protection using impressed current) a new combined protection system was developed where the principle of drying out the concrete (by means of a surface protection system) is combined with a temporary cathodic protection (by means of a sprayed zinc layer) during the transitional period of the drying out process. This new system was tested both in the laboratory and on‐site at a pilot application. Based on the results obtained the possibilities and limitations of the new system are discussed in this paper.     

Electrochemical chloride removal from reinforced concrete structures and its ability to repassivate prerusted steel surfaces

Gravimetric and electrochemical measurements were used to expose the relationship between the degree of prerusting of reinforcements embedded in chloride‐contaminated mortar or concrete and the efficiency with which they are repassivated once depassivating ions are removed. The results show that, above a certain, ill‐defined rusting threshold, the electrochemical chloride removal does not ensure effective repassivation of reinforcements in the steel/concrete system. Once the passivity of reinforcements embedded in reinforced concrete structures (RCS) is overcome, the typical corrosion rates of the active state seemingly suffice to maintain an acid pH at the metal/rust interface in the bulk of such a strongly alkaline material as concrete. After this local acidification, the metal inside pits probably behaves similarly as it would in an acid solution. As a result, it does not suffice to remove the rusting agent in RCS in order to stop corrosion; rather, the agent must be removed before the first visible signs of deterioration appear.     

Comparative study on induced macrocell corrosion phenomenon in repaired ordinary reinforced and self-compacting concrete structures

Abstract

This paper aimed at an experimental investigation of the comparative corrosion phenomenon in the reinforcing steel of repaired chloride contaminated self-compacting concrete (SCRC) and ordinary concrete (OC) patches. This research is a continuation of a previous study in which macrocell specimens were prepared with OC having different chloride contaminations simulating the actual patch repair in the construction field. Here, in this research, the same specimens were prepared with SCRC to investigate more deeply the macrocell phenomenon in SCRC, which received limited attention in the past. Four prismatic specimens with two sets of 5 and 3% chloride contaminated SCRC at the two ends were prepared respectively, and the middle portion of these specimens was cast after 24 h with uncontaminated SCRC simulating the actual patch repair in the field. After 1 year of experimental observations of corrosion potentials and corrosion rates, interesting and novel results were obtained in comparison with OC and SCRC specimens.     

Elastoplastic buckling as source of misinterpretation of micropillar tests

Microscopic compression tests (micropillar tests) are typically used to obtain stiffness and strength properties of materials at small length scales. In this work it is shown that structural effects, in particular instabilities, have implications on the resulting load–displacement diagram. Care has to be taken when the measured load–displacement path of a micropillar is interpreted as a stress–strain path of the material. Several structural effects are discussed by means of computational analysis.     

Study of cyanoethylated alfa fiber reinforced composites by dynamic mechanical analysis

Cyanoethylation of long alfa fibers was studied, and these chemically modified fibers were used to manufacture alfa-polyester composites. The dynamic mechanical thermal properties of an unsaturated polyester resin (cured) and of composites of unmodified and chemically modified alfa-polyester were studied using a dynamic mechanical analyzer over a wide temperature range. The data suggest that in spite of the fragility of the cyanoethylated alfa fibers compared to the unmodified ones, both unmodified and modified alfa-polyester composites manifest the same order of mechanical properties: T_g, tan δ and E′ values are very near in the two cases. Fragility of fibers is compensated by the better interfacial bond between the fibers and the matrix. The scanning electron micrographs of the fracture surface of the samples reveal the improved bonding at the interface between the cyanoethylated fiber and the polyester resin. The article is published in the original.