Expansion Of Corrosion Products Research Articles

Mechanical and microstructural properties of one-part geopolymer-solidified soil attacked by Na2SO4

In the construction of traffic engineering, a large amount of waste soils was generated. These soils have poor engineering properties, cannot be used as subgrade fill, so they were solidified treatment, commonly used cement curing agent have adverse effects on the environment. One-part geopolymer (OPG), as a green and new type of soil stabilizer, not only provides a new idea for the solidification of engineering waste, but also offers an effective way for the disposal of industrial solid waste, and reduces the consumption of cement. In order to evaluate the durability of geopolymer solidified soil, in this paper, with fly ash (FA) and ground granulated blast furnace slag (GGBS) as raw materials, solid NaOH and Na2SiO3 as solid alkali-activator to prepare OPG, which was used as a solidifier to solidify the waste dredged silt to produce one-part geopolymer-solidified soil (OPGSS). The variation patterns of mass, unconfined compression strength (UCS) and elasticity modulus of OPGSS with attack time under 0%, 5% and 10% Na2SO4 solutions were investigated. The changes in the phase composition, micro-morphology and pore size distribution of OPGSS were characterized by XRD, SEM-EDS and nuclear magnetic resonance (NMR). The results showed that: Under both 5% and 10% Na2SO4 solutions, the UCS of OPGSS decreased in two stages with attack time, and the number of large pores and total pores of OPGSS increased in two stages. The inflection points appeared on day 8 under 5% Na2SO4 solution; the inflection points appeared on day 5 under 10% Na2SO4 solution. This was mainly due to the expansion of corrosion products formed by OPGSS under Na2SO4 attack, which destroyed the microstructure of OPGSS and led to a reduction in the UCS of the OPGSS.

3D modelling of the interaction between bending and corrosion-induced cracks in reinforced concrete beams

Bending and corrosion-induced cracks interact and impact the durability of Reinforced Concrete (RC) beams in a complex manner. Still, research on the mechanisms behind this interaction is limited. In this study, a 3D nonlinear finite element modelling method of RC beams was developed to explore this interactive mechanism. The models were assessed against experimental benchmarks, showing good agreement in terms of crack pattern and growth. Moreover, the modelling method offered the advantage of visualising the internal condition of beams, including the propagation of internal cracks and the expansion of corrosion products represented by interface elements. A parametric study was conducted to examine the influence of three crucial factors: the transport of the corrosion products, the distance between bending cracks, and bending crack width. The modelling results revealed that the transport of corrosion products appeared to play a decisive role in the location of initiation and evolution of corrosion-induced cracks. Additionally, as the distance between the bending cracks decreased, the onset of corrosion-induced cracks transitioned from the midpoint between the bending cracks to the vicinity of them. Furthermore, an increase in bending crack width had no impact on the initiation and evolution of corrosion-induced cracks, while their widths, and variation of width along the bar, decreased.

A two-phased modelling approach for corrosion-induced concrete cracking and bond deterioration in reinforced concrete

Bond deterioration is one of the major consequences of reinforcement corrosion in reinforced concrete (RC) structures. In this paper, a two-phased numerical modelling approach is presented that aims to determine the constitutive behaviour (bond–slip) at the reinforcement-concrete interface at a certain corrosion level. The novelty of the approach is that it consists of a crack model and a bond model, and that the flow of corrosion products into the pores and corrosion-induced cracks as well as the effect of the bonded length and concrete cover are taken into account in the 2D crack model. The resulting expansion of corrosion products from the crack model is used as input in the 3D bond model. The combination of both models leads to a procedure that balances computational time and modelling detail. The model is validated on a substantial amount of experimental pull-out test results. A good agreement is obtained between the experimental data and the models for different corrosion levels in terms of crack width, crack pattern, corrosion-induced bond loss, and failure mode.

Corrosion-induced cracking behavior of lightweight aggregate concrete: Experimental and numerical study

The corrosion-induced cracking potentially undermines the durability of concrete structures, while the fracture mechanism of lightweight aggregate concrete (LWAC) differs from that of the normal concrete subjected to expansive corrosion products due to the low-strength coarse aggregate. Eleven beams considering different diameters of LWA, the volume fraction of LWA, and surface crack widths were subjected to the accelerated corrosion setup, and the corrosion-induced cracks and steel mass loss were observed. The mesoscopic finite element model was established for the analysis of LWAC, and the model was verified according to the test results. The results of numerical study showed that decrease in the strength of LWA led to the inner damage of LWAC, while the increase in cover thickness made the cracking process of LWAC more rapid. On the basis of mesoscopic simulations, the critical cracking mass loss of steel bar and the empirical cracking parameter were derived, and then the linear equations were adopted for the establishment of relations between mass loss of corroded rebar and the corrosion-induced surface crack width by considering the effect of concrete cover and the rebar spacing.

Residual bond strength in reinforced concrete cracked by expansion agent filled pipe simulating rebar corrosion

In corroded reinforced concrete, the volume of steel increases due to expansive corrosion products, leading to cracking of concrete. As a result, the bond capacity between concrete and rebar gradually decreases. Previously, the author explored bond deterioration owing to corrosion-related cracking using a novel crack simulation approach. To simulate the volumetric expansion of the rebar due to corrosion, an aluminum pipe is inserted into the concrete and filled with an expansion agent. However, the previous study did not consider the important effect of stirrups that provide confinement and improve bond strength. To address this limitation, pull-out tests were performed on 48 cracked specimens to investigate bond deterioration considering the influence of crack width and stirrup. It is concluded that the induced cracks without corrosion products can measure the exclusive result of corrosion of the rebar itself. After cover cracking, stirrups become the primary confinement source and can help reduce bond deterioration. Finally, an empirical formula was proposed to evaluate the bond strength degradation with induced crack width and stirrups being the main parameters. Comparisons with various experimental results of corroded specimens confirm that the proposed formula can give satisfactory predictions.

Impact of Corrosion on the Bond Strength between Concrete and Rebar: A Systematic Review.

Corrosion of the reinforcement affects more than the cross-sectional area of the rebar. The volume of steel also increases due to expansive corrosion products, leading to the cracking, delamination, and spalling of concrete. As a result, the bond capacity between concrete and rebar is affected. Researchers have extensively examined the impact of corrosion on the bond strength between concrete and rebar to propose empirical, theoretical, or numerical predictive models. Therefore, research programs on this topic have increased rapidly in recent years. This article presents a systematic literature review to explore experimental methods, outcomes, and trends on this topic. The Web of Science search collected 84 relevant research articles through a rigorous selection. Key factors that affect bond strength degradation, including concrete cover, concrete strength, and stirrups, have been documented. However, a general model is still unavailable due to discrepancies caused by differences in testing methods to evaluate the effect of corrosion on bond strength. Furthermore, researchers attempted to clarify the degradation mechanism of bond strength affected by corrosion. As a result, new alternatives have been proposed to build a practical model to assess the bond strength deterioration of corroded structures.

Modeling of Cover Concrete Cracking Due to Uniform Corrosion of Reinforcement

Cracking of cover concrete due to the corrosion of reinforcing steel is one of the main causes of deterioration in Reinforced Concrete (RC) structures. An outbound stress is developed in concrete surrounding the reinforcing steels due to the expansive corrosion products of reinforcement leading to cracking of the concrete cover. In this paper, the cracking pressure was simulated through a finite element modeling. The effect of geometrical and material parameters, i.e. concrete cover thickness, bar diameter, and concrete tensile strength, on the cracking pressure was also investigated. Abaqus 6.14 was used as modeling platform. The cracking pressure was found to dependent on the cover thickness and tensile strength of concrete. A higher pressure was required to initiate crack for a higher cover thicknesses and tensile strength. The cracking pressure was decreased with the increase in bar diameter. Finally the crack initiation and propagation has been simulated successfully for different arrangements of reinforcements.
 Journal of Engineering Science 12(1), 2021, 43-49

A stochastic multiscale peridynamic model for corrosion-induced fracture in reinforced concrete

Concrete fracture caused by corrosion of reinforcing bars may cause subsequent structure failure. To better predict this process, we introduce a partially-homogenized stochastic peridynamic model with the simplest constitutive relation (linear elastic with brittle failure). The model links microscale information (phase volume fractions of mortar, aggregates, interfaces) to macroscale fracture behavior, while costing the same as a fully homogenized model. We explain why a fully-homogenized peridynamic model fails to capture the correct concrete fracture modes/patterns, while the new model succeeds. The multiscale model predicts the evolution of fracture in reinforced concrete caused by corrosion products expansion in samples with a single or multiple rebars. Non-uniform expansion of corrosion products is enforced here as preset, incremental radial displacements. The computed fracture patterns and the order in which various cracks develop match what is seen in experiments. The model’s robustness is tested under different stochastic realizations and discretization grid types.

Proračun prodora klorida u beton

Na armiranobetonskim konstrukcijama izloženim agresivnom okolišu često nastaju oštećenja uslijed korozije armature izazvane kloridnim ionima. Oštećenja nastaju u obliku pukotina i odlamanja zaštitnog sloja betona uslijed bubrenja produkata korozije, što nepovoljno utječe na nosivost i trajnost konstrukcije. Povrh toga, površina poprečnog presjeka armature smanjuje se istovremeno s procesom degradacije betona. No, oštećenja se javljaju neposredno nakon depasivacije čelika uslijed kritične koncentracije kloridnih iona u blizini armature. Vrijeme koje je potrebno da kritična koncentracija kloridnih iona prodre do armature naziva se faza inicijacije, a osnovni cilj ovog rada je procjena njezinog trajanja. Trajanje faze inicijacije moguće je predvidjeti ukoliko se u obzir uzmu transportni procesi koji se odvijaju kroz zaštitni sloj betona. Najvažniji fizikalni procesi vezani uz fazu inicijacije su transport kapilarne vode, kloridnih iona te topline. Stoga je u okviru ovog rada razvijen 2D numerički model pomoću metode konačnih razlika, koji simulira navedene transportne procese. Primjena modela pokazana je na numeričkom primjeru u kojem je kvadratni poprečni presjek armiranobetonskog stupa izložen agresivnim morskim uvjetima. Proračun je proveden kako bi se istražio utjecaj širine pukotina na trajanje faze inicijacije. Numerički rezultati pokazuju da raspucalost zaštitnog sloja betona značajno smanjuje trajanje faze inicijacije, a samim time i uporabni vijek konstrukcija.

New NaCl-simulated concrete pore solution (New NaCl-SPS) for superhydrophobic coating of galvanized steel

An anti-corrosive superhydrophobic surface was successfully fabricated on a galvanized coating of a porcelain insulator’s pin in HVAC transmission line, using the New NaCl-SPS immersion method and stearic surface modification. After 3 days immersion in New NaCl-SPS solution, the stable passive layer was formed on the galvanized surface and it was confirmed as highly crystallized ZnO layer with hexagonal wurtzite structure, which is environmentally friendly. This work represents a new route for the synthesis of ZnO micro and nano-structures on the galvanized coating by immersion in New NaCl-SPS solution. Moreover, the superhydrophobic surface has been successfully fabricated on the synthesized ZnO surfaces. The corrosion resistance of galvanized surfaces with or without superdydrophobicity has been investigated. The results demonstrate that the superhydrophobicity can effectively enhance corrosion resistance, to counter pin corrosion problems of electrical insulators and porcelain breakage by volume expansion of corrosion products on the zinc sleeve.

Key inhibitory mechanism of external chloride ions on concrete sulfate attack

To explore the key inhibitory mechanism of external chloride ions on concrete sulfate attack, long-term partial- and full-immersion experiments of concrete in chloride solutions and chloride and sulfate composite solutions were performed. As corrosion time begins, visual inspection, compressive strength, and ultrasonic velocity were periodically observed or tested. Moreover, the micro-morphology, the contents of Cl and S elements in concrete, and the transport speeds of Cl− and SO42− ions through concrete were investigated by using scanning electron microscope, X-ray fluorescence spectrum, and chemical analysis. Chloride ions neither have corrosive effects on concrete nor effects on concrete physical and mechanical properties, which is the prerequisite for chloride ions in inhibiting concrete sulfate attack. In the case of combined solutions, the transport speed of Cl− ions into concrete is evidently higher than that of SO42− ions. Then, chloride ions enter concrete early and form Friedel's salt with AFm or with C3A and Ca(OH)2 in concrete, which inhibits the transport of SO42− ions into concrete and reduces the formation of expansive corrosion products of ettringite or gypsum. Thus, the sulfate attack on plain concrete is alleviated. Based on the inhibitory mechanism of Cl− ions on concrete sulfate attack, the presence of Cl− ions cannot completely avoid concrete sulfate attack but can partially reduce sulfate risk on concrete.

3D finite element modelling of corrosion of lap splice joints in concrete

The paper presents a numerical study of the chloride induced corrosion process in lap splice joints in concrete. The problem is simulated using a recently developed 3D Chemo-Hygro-Thermo-Mechanical (CHTM) model for concrete, which is employed to simulate accelerated corrosion, the same as performed in the experimental test taken from the literature. For different corrosion levels, corrosion current density, rust production, expansion of corrosion products, stresses induced in concrete and corrosion induced damage of concrete are calculated. The corrosion induced cracking of concrete cover is compared with the experimental results and good agreement between experimental observations and numerical simulations is obtained.

The Effects of Salt Crystallization in Ceramic Bricks in Terms of Line Deformations

The long life of bricks in different conditions, especially in the presence of moisture, promotes progressive changes in ceramic material. Over time it can cause a gradual loss of the original performance of bricks. This process is related to, inter alia, the accumulation of salt originating from the external environment in ceramic texture. The crystallization of salts in the bricks and the related process of changes in volume of ceramic material can be the reason for pressure crystallization. In addition, expansive corrosion products can form in the reaction of salts and components of ceramic body. This causes the creation of stresses in the material and its cracking. Therefore, studies were undertaken, whose aim was to determine the size of line deformation changes of ceramic materials caused by the accumulation of various salts in the bricks of different textures. The periodic exposure to corrosion of ceramic materials in solutions of NaCl and MgSO4 by alternately saturating and drying were conducted.The scope of research included determined changes of linear deformations of studied bricks, caused by crystallization of salts of sulfate, chloride, or both. As a diagnostic characteristic of the changes, measurement results of elongation samples with dimensions 250x30x65mm cut from a brick were adopted. Based on the obtained results it has been shown that crystallization of both salts in ceramic materials increases the dimensions of bricks. The greatest deformations of bricks throughout the study period were recorded in the case of chloride salts. It was further found that exposure to corrosion leads to strong deformations and destructions of bricks in the long term. This was observed particularly in the case of the brick samples subjected to a corrosive environment containing both sulfate ions and chloride. In order to determine the causes of differentiated resistance of the bricks in corrosive environments (resulting changes of dimensions), studies on the porosity, compressive strength, tensile strength, modulus of elasticity of the bricks and observations of their microstructure were performed.

Analytical modelling of bond stress at steel concrete interface due to corrosion

AbstractAn analytical model is proposed for bond stresses at the corroded steel‐concrete interface in reinforced concrete. The concrete around the corroded bar is modelled as a thick‐walled cylinder – consisting of an inner cylinder of an anisotropic material and an outer cylinder made of an isotropic material – subjected to internal pressure exerted by the growth of corrosion products on the concrete wall at the interface. A frictional model is used to combine the action of confining pressure due to radial pressure produced by principal bar ribs and the pressure resulting from expansion of corrosion products. The analysis results using the proposed model show good agreement with the experimental results of several researchers.

Studies of the radioactive waste confinement matrix using neutron scattering methods

The management of the radioactive waste implies the conditioning in a cement matrix as an embedding, stable, disposal material. Cement matrix is the first and most important engineering barrier against the migration in the environment of the radionuclides contained in the packages. Chemically, after mixing with water, cement produces a reacting matrix with a porous microstructure. Knowing how the microstructure develops is therefore desirable in order to assess the compatibility of radioactive streams with cement and predict waste form performance during storage and disposal. This article highlights the work performed in SANS investigation of a new type of cements to be used for conditioning of aluminium waste coming from reactor decommissioning activities. It is well known that the expansion of corrosion products formed on aluminium can lead to cracking of the waste form.

Estimating Critical Corrosion for Initiation of Longitudinal Cracks in RC Structures Considering Phases and Composition of Corrosion Products

AbstractPremature deterioration and reduction in the life of reinforced concrete (RC) structures due to corrosion of the embedded reinforcing steel bars is a major concern across the world, and the time for formation of longitudinal cracks has been largely accepted as the “service life” of the structure. It is also widely known that the formation and deposition of expansive corrosion products (of iron) on the bars exert radial pressure on the cover concrete, which finally cracks. In this case, it is reasonable to assume that the composition of the corrosion products, in terms of the different phases of the oxides and hydroxides, and their relative percentages, play a vital role in determining the loss of weight (of iron) that causes sufficient pressure for the onset of such longitudinal cracks. It is interesting that virtually no quantitative information is available in the literature on this subject. The main thrust of the present work is to understand the effect of composition and relative amount of dif...

Modelling processes related to corrosion of reinforcement in concrete: coupled 3D finite element model

Aggressive environmental conditions, such as exposure to the sea climate or use of de-icing salts, have a strong influence on durability of reinforced concrete (RC) structures due to reinforcement corrosion-induced damage. In the present paper, a recently developed three-dimensional (3D) chemo-hygro-thermo-mechanical model for concrete is briefly discussed. The model was implemented into a 3D finite element code and its application is illustrated through numerical analysis of a RC beam-end specimen with stirrups, exposed to aggressive environmental conditions. Damage of concrete cover due to expansion of corrosion products and transport of rust through concrete pores and cracks are computed. Subsequently, the influence of corrosion-induced damage of concrete cover on pull-out resistance of deformed reinforcement is investigated. The comparison between numerical results and experimental evidence shows that the complex coupled mathematical model is able to realistically predict the phenomena related to corrosion of steel reinforcement in concrete.

EXPERIMENTAL STUDY ON THE REHABILITATION OF CORRODED REINFORCED CONCRETE BEAMS USING FIBER REINFORCED POLYMER

The purpose of this research is to investigate rehabilitation of corrosion-damaged R.C. beams with carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP), the effects of CFRP and GFRP amounts on flexural behavior of the beams and summarize the results of a multi-phase experimental program to investigate the viability of using externally bonded fiber reinforced polymer (FRP) laminates to rehabilitate corrosion-damaged reinforced concrete beams. Twenty reinforced concrete test specimens (100 × 150 × 1200 mm) were constructed, ten of them were subjected to an aggressive environment for 13 month, The reinforcement of the four specimens was subjected to accelerated corrosion by means of impressed (D/C) current up to 5% mass loss, four specimens were not subjected to any corrosion and strengthen by the same schemes of repaired, and the remaining two specimens were not subjected to any corrosion and were not strengthened (control). After being corroded, the beams were repaired by externally epoxy bonding FRP laminates to the concrete surface using two different schemes. Half-cell potential have been measured as metric of performance of the samples. Strain gauges were used on the concrete and FRP laminates to measure strain on beams. The specimens were tested in flexure in a four-point bending system. The results showed that FRP laminates successfully confined the corrosion cracking and spalling due to expansion of corrosion products. The FRP strengthened and repaired beams exhibited increased stiffness and ultimate strength over the unstrengthened specimens. The use of FRP sheets for repairing corroded reinforced concrete beams is an efficient technique to maintain structural integrity and enhance the behavior of such beams

Seismic Fragility Assessment of RC Bridges under Marine Environments

The chloride-induced corrosion of steel bars is focused in this study which is one of the major causes of deterioration of RC bridges under marine environments. The steel corrosion usually causes cracking and spalling of the concrete cover due to the expansion of corrosion products. Structural distress due to loss of bond or reduction of the cross-sectional area can be caused with time. A girder bridge exposed to the marine environment is studied to present the fragility curves variance in time in this study. The damage states of the bridge are determined to five stages by using the maximum displacement ductility. The proposed method will be useful to evaluate the seismic performance of new or existing bridges considering steel rebar corrosion.

Corrosion inhibition of steam generator tubesheet by Alloy 690 cladding in secondary side environments

Denting is a phenomenon that a steam generator tube is distorted by a volume expansion of corrosion products of the tube support and tubesheet materials adjacent to the tube. Although denting has been mitigated by a modification of the design and material of the tube support structures, it has been an inevitable concern in the crevice region of the top of tubesheet. This paper provides a new technology to prevent denting by cladding the secondary surface of the tubesheet with a corrosion resistant material. In this study, Alloy 690 material was cladded onto the surface of an SA508 tubesheet to a thickness of about 9mm. The corrosion rates of the original SA508 tubesheet and the Alloy 690 clad material were measured in acidic and alkaline simulated environments. Using Alloy 690 cladding, the corrosion rate of the tubesheet within a magnetite sludge pile decreased by a factor of 680 in 0.1M NiCl2 solution at 300°C, and by a factor of 58 in 2M NaOH solution at 315°C. This means that denting can drastically be prevented by cladding the secondary tubesheet surface with corrosion resistant materials.