Corrosion performance of reinforced mortar in the presence of polymeric nano-aggregates: electrochemical behavior, surface analysis, and properties of the steel/cement paste interface

This study reports on the effect of admixed polyethylene oxide-b-polystyrene (PEO₁₁₃-b-PS₇₀) micelles on corrosion behavior of reinforced mortar. The electrochemical measurement shows that the corrosion performance of the reinforcing steel was not significantly improved. However, surface analysis and microstructural investigation at the steel/cement paste interface reveal that the admixed micelles lead to a steel surface layer with enhanced barrier properties in terms of morphology and composition. Therefore, the presence of micelles further minimized and halted the corrosion process, despite the very aggressive, chloride-containing environment of 5% NaCl. The reasons and mechanisms behind the hereby observed corrosion behavior of reinforced mortar in the presence of micelles are related to the influence of these nano-aggregates on microstructural properties. These further results in altered water/ion transport and chloride-binding mechanisms in the bulk mortar matrix and thus steel product layer modifications towards enhanced corrosion resistance.     

Corrosion products that form on steel within cement paste

Most research on chloride-induced corrosion of reinforcing steel is conducted either in simulated pore solution or concrete. The former has the disadvantage that the experiments cannot replicate the environmental variations on the surface of the steel induced by the presence of the cementitious cover. The difficulty with the latter is that it is impossible to clearly assess the impact of many different parameters that influence the corrosion in commercial concrete. Consequently, the present study involves steel plates embedded in cement paste to minimize the number of active corrosion sites relative to steel in pore solution, thus simplifying an investigation into the location and accumulation of corrosion products in the cement paste and the influence of cracks on the corrosion process.Corrosion monitoring techniques (i.e., open circuit potential mapping, linear polarization resistance) were correlated with chemical and microstructural analyses, including Raman spectroscopy of the corrosion products, to study the specimens. The results indicate the following: a range of corrosion products forms, primarily within shrinkage cracks; their specific volumes are typically in the range of 2 to 3; cracks had a greater impact on the corrosion rate of steel in white cement than in Type 10 cement; and that the surface sealing of the cracks using epoxy did not prevent corrosion initiation from occurring under the epoxy.     

Inhibition of Corrosion of Mild Steel in Hydrochloric Acid Solution Using Akee Apple Seed Extract

The inhibiting action of Akee apple (Blighia sapida) seed extract (AASE) on corrosion of mild steel was investigated in 2 M hydrochloric acid solution using weight loss and thermometric measurements. The study was carried out at temperatures of 30 and 60 °C with concentration of inhibitor varied from 0.1 to 0.5 g/l in the acidic medium. The results of the study showed that the corrosion rate of mild steel decreased in the presence of the inhibitor but increased with increase in temperature. The inhibitor exhibited excellent inhibition efficiency on mild steel corrosion as 86.90 and 75.87% of inhibition efficiency were achieved with addition of 0.5 g/l concentration of the inhibitor at 30 and 60 °C temperature, respectively. The inhibitive adsorption parameters established that the AKEE obeyed the Langmuir adsorption isotherm with physical adsorption mechanism and the result of Gibbs free energy of adsorption (?G_ads) revealed an endothermic reaction and spontaneous process of adsorption.     

Penetration resistance and electrical resistivity of cement paste with superplasticizer

The purpose of this paper is to investigate the setting process and evolution of electrical resistivity of Portland cement pastes with constant water to cement ratio (w/c) of 0.3 and with different dosages of naphthalene superplasticizer (SP) from 0 to 1.2 %. The setting process of cement paste was monitored by the Vicat needle test. The depth of penetration was recorded and used to calculate the shear resistance generated by the cement paste. Electrical resistivity was measured by a non-contacting electrical resistivity apparatus. The hyperbolic curve of electrical resistivity versus time was plotted to determine the ultimate electrical resistivity. The results show that the addition of SP to the pastes with a fixed w/c can cause longer setting time and delay the evolution of electrical resistivity. The final setting time (t _f) and the occurring time of maximum rate of electrical resistivity (t _r) were both delayed when the dosage of SP was increased. This may indicates that the electrical resistivity measurement can be used to monitor the setting process of cement. The compressive strength at 28 days and the ultimate electrical resistivity show a same tendency for the cement pastes with different dosages of SP. Thus, it would be possible to predict the compressive strength of hardened cement paste by its ultimate electrical resistivity.     

Corrosion behaviour of steel in high alumina cement mortar cured at 5,25 and 55 °C: chemical and physical factors

The corrosion behaviour of embedded steel was related to the composition of the pore phase in equilibrium with the hydrated phases and the porosity of the high alumina cement mortars subsequent to curing at 5,25 and 55 °C. The corrosion of reinforcements was evaluated by electrochemical techniques. The effect on corrosion of 3% by weight of cement of NaCl, added during the mixing process, and of the accelerated carbonation of mortars in CO₂ atmosphere were also determined. The pH value and the chemical composition of pore fluid of plain high alumina cement (HAC) mortar cured at all three temperatures suggested that the embedded steel was in a passivated state. The resistance of HAC to carbonation and its greater potential for chloride binding by chloroaluminate formation are believed to make HAC inherently more protective to steel, relative to normal Portland cement, during ingress of chloride from external sources. High corrosion rates reported in literature for steel embedded in HAC may be attributable to bad practice, not to lack of passivity.     

A short-term test method to determine the chloride threshold of steel–cementitious systems with corrosion inhibiting admixtures

Now-a-days, multiple types of corrosion inhibiting admixtures (CIAs) are being used to enhance the chloride threshold (Cl_th) of steel–cementitious systems. However, due to the application of external potential to drive chlorides, some existing short-term test methods are not suitable to assess the Cl_th of S–C systems with CIAs containing anions. This paper presents the development of a Modified Accelerated Chloride Threshold (mACT) test to determine the Cl_th for S–C systems with CIAs. The test specimens consisted of a mortar cylinder with an embedded steel piece and electrodes forming a 3-electrode corrosion cell. The specimens were exposed to chloride solution and the linear polarization resistance tests were conducted every 3.5 days. The corrosion initiation was detected using statistical analysis of the repeated R _p measurements. After corrosion initiation, the chloride content in mortar adjacent to the embedded steel piece was determined and defined as Cl_th. The time required to complete mACT test for an S–C system with CIAs is about 120 days. The Cl_th of eight specimens each with S–C system containing (i) without inhibitor, (ii) anodic inhibitor [calcium nitrite] and (iii) bipolar inhibitor [both calcium nitrite and amino alcohol] were determined. Both anodic and bipolar CIAs showed enhanced corrosion resistance. Also, the bipolar inhibitor performed better than anodic inhibitor. It was concluded that the use of CIAs could significantly delay the initiation of chloride-induced corrosion. The mACT test can be used to determine the Cl_th and estimate the service life during the planning and design stages of a project and help select durable materials.     

Interface between zinc phosphate-deposited steel fibres and cement paste

In an attempt to protect steel fibre reinforcements from corrosion and improve their adherence to cement pastes, we deposited a zinc phosphate (ZnPh) conversion coating on the surface of the fibres. At the interfacial contact zones between the cement paste and ZnPh, alkali-induced dissolution caused the dissociation of abundant PO ₄ ^3– ions from the ZnPh. The interaction of PO ₄ ^3– ions with Ca²⁺ ions from the pastes led to the formation of hydroxyapatite and brushite in the vicinity of the dissolved ZnPh surface. Such intermediate calcium phosphate compounds played important roles in (1) improving the cement-fibre interfacial bonds, and (2) repairing the damage of the ZnPh surfaces dissolved by alkali. These processes protected the steel fibre from corrosion.     

偏高岭土对水泥砂浆中钢筋钝化的影响

利用电化学阻抗谱、循环动电位极化、阴极极化、热重和XRD等方法,研究了偏高岭土(MK)掺量(占MK/水泥总质量的20wt%、30wt%、40wt%)对钢筋-MK/水泥砂浆中钢筋钝化膜形成及其耐蚀性能的影响。结果表明:在一般环境中,钢筋在不同MK掺量的钢筋-MK/水泥砂浆中均可以形成稳定的钝化膜;在质量分数为3.5wt%的NaCl溶液环境中,MK掺量过多会使钢筋-MK/水泥砂浆中钢筋的钝化膜稳定性降低,耐蚀性能下降。从钢筋钝化膜稳定角度考虑,在氯盐环境中,水泥基材料中MK掺量应予以限制。      

Evaluation of the Corrosion Protection Performance of Epoxy-Coated High Manganese Steel by SECM and EIS Techniques

The corrosion protection performances of epoxy-coated Mn steel and carbon steel were evaluated by electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) analysis. EIS was performed on coated Mn steel with a scratch in a 0.1 M NaCl solution after a wet/dry cyclic corrosion test. The charge transfer resistance (R _ct) and film resistance (R _f) of the coated Mn steel displayed a higher value than the coated carbon steel. The increase in the charge transfer resistance and film resistance of the coated steel is due to the presence Mn in steel. SECM was conducted to estimate the corrosion protection performance of the epoxy-coated Mn steel immersed in a 0.1 M NaCl solution. It was found that dissolution of Fe²⁺ was suppressed at the scratch on the coated Mn steel due to the higher resistance for anodic dissolution of the substrate. SEM/EDX analysis showed that Mn was enriched in corrosion products at a scratched area of the coated steel after corrosion testing. FIB-TEM analysis confirmed the presence of the nanoscale oxide layer of Mn in the rust of the steel, which had a beneficial effect on the corrosion resistance of the coated steel by forming protective corrosion products in the wet/dry cyclic test.     

Air-foamed calcium aluminate phosphate cement for geothermal wells

Air-foamed low-density calcium aluminate phosphate (CaP) cement slurry was prepared by mixing it with chemical foaming reagent at room temperature without any pressure, followed by autoclaving at 200 °C. When the porosity, compressive strength, and water permeability of the autoclaved CaP foam cement made from a 1.22 g/cc slurry density was compared with those of N₂ gas-foamed Class G cement made from a slurry of similar density under high pressure and hydrothermal temperature at 288 °C, the CaP cement revealed some advanced properties, such as a higher compressive strength and lower porosity. These advanced properties were due to the hybrid formation of three crystalline hydrothermal reaction products; hydroxyapatite, boehmite, and hydrogarnet phases. However, one shortcoming was an increase in water permeability because of the formation of an undesirable continuous porous structure caused by coalesced air bubble cells, suggesting that an appropriate lesser amount of foaming reagent be used to create a conformation in which fine discrete air-bubble cells are uniformly dispersed throughout the slurry. For non-foamed cement, three major factors contributed to protecting carbon steel against corrosion: (1) good adherence to steel, reflecting a high extent of coverage by the cement layer over the steel’s surfaces; (2) retardation of cathodic corrosion reactions; and, (3) minimum conductivity of corrosive ionic electrolytes. However, adding an excessive amount of foaming reagent did not offer as effective corrosion protection as that of non-foamed cement.     

Influence of pozzolana on sulfate attack of cement stone affected by chloride ions

This study investigated the influence of natural pozzolana (opoka) additive on the hydration of Portland cement and the effects of pozzolana on sulfate attack of cement stone affected by chloride ions. In the samples, 25 % (by weight) of the Portland cement was replaced with pozzolana. The specimens were hardened for 28 days in water, and then one batch was soaked in a saturated NaCl solution and another in a 5 % Na₂SO₄ solution for 3 months at 20 °C. After being kept for 3 months in a saturated NaCl solution, samples were transferred to a 5 % Na₂SO₄ solution and kept under these conditions for 3 months. It was estimated that under normal conditions, pozzolana additive accelerated the hydration of calcium silicates and initiated the formation of CO₃ ^2?–AFm; opoka also decreased the threshold pore diameter of hardened Portland cement paste. It was found that Cl^– ions penetrate to monosulfoaluminate, form Friedel’s salt, and release SO₄ ^2? ions, which react with unaffected monosulfoaluminate and form extra ettringite; when samples were transferred to the 5 % Na₂SO₄ solution, a greater quantity of new ettringite was formed. Meanwhile, pozzolana additive reduced the penetration of chloride and sulfate ions into the structure of Portland cement hydrates and inhibited sulfate attack of cement stone treated in a saturated NaCl solution.     

Shrinkage of steel fibre reinforced cement composites

The paper presents results of an experimental investigation on the influence of steel fibres on the free shrinkage of cement-based matrices. Shrinkage tests were carried out on cement paste, mortar and two types of concrete mixes for a period of up to 520 days. Melt extract, crimped and hooked steel fibres were used for reinforcement at volume fractions ranging between 1 and 3%. The results indicate that fibres restrain the shrinkage of the various cement matrices to a significant extent, resulting in reductions of up to 40%. Crimped fibres are the most efficient in providing shrinkage restraint. The paper also presents a theoretical expression and an empirical expression which can be used to predict shrinkage strains of steel fibre reinforced cement matrices. The analysis requires a knowledge of the values of coefficient of friction, μ, at the fibre-matrix interface, which are also derived in this paper. The μ values for steel fibres in normal concrete, mortar and cement paste range between 0.07 and 0.12.     

A method for predicting the alkali concentrations in pore solution of hydrated slag cement paste

The alkalinity of the pore liquid in hardened cement paste or concrete is important for the long-term evaluation of alkali-silica reaction (ASR) expansion and corrosion prevention of steel bar in steel reinforced structures among others. It influences the reactivity of supplementary cementitious materials as well. This paper focuses on the alkali binding in hydrated slag cement paste and a method for predicting the alkali concentrations in the pore solution is developed. The hydration of slag cement is simulated with a computer-based model CEMHYD3D. The amount of alkalis released by the cement hydration, quantities of hydration products, and volume of the pore solution are calculated from the model outputs. A large set of experimental results reported in different literatures are used to derive the alkali-binding capacities of the hydration products and practical models are proposed based on the computation results. It was found that the hydrotalcite-like phase is a major binder of alkalis in hydrated slag cement paste, and the C?CS?CH has weaker alkali-binding capacity than the C?CS?CH in hydrated Portland cement paste. The method for predicting the alkali concentrations in the pore solution of hydrated slag cement paste is used to investigate the effects of different factors on the alkalinity of pore solution in hydrated slag cement paste.     

Corrosion Inhibition of mild steel in aqueous solution containing H2S by some naturally occurring substances

The corrosion inhibition of mild steel by some naturally occuring substance was evaluated in absence and presence of 600 and 1200 mg H₂S/l in 3% NaCl aqueous solution and pH of 3 and temperature of 25 °C. These naturally occurring substance included the water extracts, coumarines and fatty matters extracts of some Egyptian plants. These plants included: (1) Nigella Sativa (Family Ranunculacease) (Extract (1), 2) Coriandrum Sativum (Family Umbelliferea) (Extract II), 3) Ricinus communis (Family Euphorbiaceae) (Extract III). The galvanostatic anodic and cathodic polarization measurements were used for studying the corrosion behavior of mild steel and evaluation of the percentage inhibition of the undertesting extracts of these three plants and also preparation of fatty matters and coumarin fractions were mentioned.     

Hydrophobic and water-resisting behavior of Portland cement incorporated by oleic acid modified fly ash

The water-repellent and anti-permeability properties of cement are crucial for the durability and safety of concrete structures. In this work, we prepared a hydrophobic Portland cement by using oleic acid as a modifier for fly ash and examined the properties of the cement paste samples. Fly ash was firstly reacted with oleic acid by the dry milling method, and the modified fly ash was used to prepare the hydrophobic Portland cement. The IR spectra confirmed that the surface of fly ash was successfully capped with oleic acid, and carboxylic acid moieties were bonded with ≡SiOH and neutralized. The TG-DSC results showed that the amount of oleic acid loaded on the fly ash beads was 7.21 wt%. Fly ash dispersed evenly in the prepared cement paste samples and the distance between beads ranged in 2–10 μm. The water contact angle of the cement paste samples increased with rising content of modified fly ash, which demonstrated good water-repellent behavior. Different cement sections showed similar water-repellent behavior, which proved that the inner structure of the cement was also hydrophobic. Using the fly ash modified with oleic acid significantly decreased the water uptake and gas permeability of the prepared cement paste samples. The hydrophobic cement sample was optimal when the content of the modified fly ash in the cement was 12 wt% and after the cement was cured for 28 days.     

Electrochemical monitoring of corrosion of steel in microsilica cement pastes

The corrosion behaviour of steel in hardened cement pastes containing various proportions of microsilica and sodium chloride has been studied by corrosion potential and linear polarisation measurements. Replacement of increasing proportions of Portland cement with microsilica in pastes of constant total chloride content and water content caused the ratio of free chloride ion concentration to hydroxyl ion concentration in the pore water to increase. This tended to destabilise the passivity of steel during the early stages of hydration but the effect became less significant as curing progressed. It is suggested that the growth of anodic pits may be restrained in microsilica cement pastes owing to the fine pore structure of the material which limits the mobility of chloride ions near the surface of embedded steel.

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Résumé On a étudié la corrosion de l'acier doux dans quelques pates de ciment Portland mélangé dans des proportions de poids différentes à de la poudre de silice (0–30%) avec une proportion constante d'eau, équivalente à 50% des poids combinés du ciment et de la poudre de silice. Dans certains cas, l'eau du mélange contenait du chlorure de sodium en quantités qui correspondaient à 0,4 ou 1% d'ions de chlorure, exprimés en pourcentages des poids combinés du ciment et de la poudre de silice. Dans une recherche précédente on avait déterminé les concentrations dissoutes de Na⁺, K⁺, Ca²⁺, OH⁻, Cl⁻, SO ₄ ²⁻ dans les solutions interstitielles capillaires des échantillons. A la suite de ce travail on a constaté que la proportion [Cl⁻]/[OH⁻] s'accroissait en fonction de la proportion de silice présente dans les échantillons. Par conséquent on s'attendait à ce que la destruction de la couche d'oxyde passivant à la surface de l'acier devienne plus probable en fonction de la proportion de silice. Pour examiner cette hypothèse, on a évalué les tensions d'électrode de l'acier enrobé et les intensités de sa corrosion par une méthode électrochimique. Bien entendu, les résultats ont indiqué que le remplacement partiel du ciment Portland par de la poudre de silice causait l'affaiblissement de la passivation du métal pendant les quelques semaines suivant la préparation des échantillons. Cependant, pour tous les échantillons qui contenaient 0 ou 0,4% de Cl⁻, l'intensité de corrosion diminuait ensuite vers le niveau qui correspondait à la passivation de l'acier. On a évalué la signification de ces résultats.

     

Experimental Study on the Effect of the Water-Cut Conditions on the Performance of L80 Carbon Steel

In the oil production, water and acidic gases, i.e., H₂S and CO₂, are co-produced with the oil. The acidic gases are known to associate with a variety of corrosion damage to the surface facilities leading to costly failures. Also, the acidic gases cause a reduction in the service life of equipment. Corrosion of API L80 tubular carbon steel in sweet media (in the presence of CO₂ gas) was investigated using the linear polarization resistance meter. Experiments using API L80 tubular carbon steel material were carried out in a stagnant flow condition with different ratios of produced water to crude oil at relatively high temperatures (60 °C up to 90 °C). The pressure was about 200 psi (13.8 bar) of CO_2, and the experiments were carried out using a high pressure vessel namely an autoclave cell. Under those experimental conditions, results indicated that at a temperature of 60 °C, the corrosion rate for carbon steel L80 increased as water-cut ratio increased. Also, the results showed that at higher temperature than 60 °C, the formation of iron carbonate scale on the surface of the steel was observed to increase. Consequently, the corrosion rate of the L80 carbon steel was observed to decrease.     

Stress corrosion cracking and hydrogen embrittlement cracking of welded weathering steel and carbon steel in a simulated acid rain environment

Abstract

The stress corrosion cracking (SCC) and hydrogen embrittlement cracking (HEC) characteristics of welded weathering steel and carbon steel were investigated in aerated acid chloride solution. The electrochemical properties of welded steels were investigated by polarisation and galvanic corrosion tests. Neither weathering steel nor carbon steel showed passive behaviour in this acid chloride solution. The results indicated that weathering steel had better corrosion resistance than carbon steel. Galvanic corrosion between the weldment and the base metal was not observed in the case of weathering steel because the base metal was anodic to the weldment. However, the carbon steel was susceptible to galvanic corrosion because the weldment acts as an anode. Slow strain rate tests (SSRT) were conducted at a constant strain rate of 7.87 × 10⁷ s^-1 at corrosion potential, and at potentiostatically controlled anodic and cathodic potentials, to investigate the SCC and HEC properties in acid chloride solution. The welded weathering steel and carbon steel were susceptible to both anodic dissolution SCC and hydrogen evolution HEC. However, weathering steel showed less susceptibility of SCC and HEC than carbon steel at anodic potential because of Cr and Cu compounds in the rust layer, which retarded anodic dissolution, and at cathodic potential due to the presence of Cr, Cu, and Ni in alloy elements, which inhibit the reduction of hydrogen ions. SEM fractographs of both steels revealed a quasicleavage fracture in the embrittled region at applied anodic and cathodic potentials.     

Corrosion Inhibition of Mild Steel by Amphoteric Surfactants

The corrosion inhibition of mild steel, in 3 % NaCl solution of pH3, by amphoteric surfactants was evaluated in absence and in presence of 600 and 1200 mg H₂S/l and at temperatures of 25, 40 and 65°C. These surfactants have the general formula. The presence of surfactants in the aqueous solution affected both the cathodic and anodic polarization areas, the corrosion potential. E_corr, shifted to more positive values and i_corr, decreased with the increase of surfactants concentrations. These surfactants have a good ability to form protective layer on the metal surface even in the presence of small concentrations of the surfactant. This was attributed to the amphoteric properties of the surfactants which contain both anionic and cationic moiety in the same molecule and also to the pressure of Cl⁻ ions in the aqueous solution. The inhibiting efficiency of the surfactants increased with the increase of the length of alkyl groups (R) in the surfactant. The value of P.I. increased to some extent in synergistic effect.     

Enhanced resistance of 2205 Cu-bearing duplex stainless steel towards microbiologically influenced corrosion by marine aerobic Pseudomonas aeruginosa biofilms

An antibacterial 2205-Cu duplex stainless steel(DSS)was shown to inhibit the formation and growth of corrosive marine biofilms by direct contact with copper-rich phases and the release of Cu~(2+)ions from the2205-Cu DSS surface.In this work,the microbiologically influenced corrosion(MIC)resistance of 2205-Cu DSS in the presence of the corrosive marine bacterium Pseudomonas aeruginosa was investigated.The addition of copper improved the mechanical properties such as the yield strength,the tensile strength and the hardness of 2205 DSS.Electrochemical test results from linear polarization resistance(LPR),electrochemical impedance spectroscopy(EIS)and critical pitting temperature(CPT)measurements showed that 2205-Cu DSS possessed a larger polarization resistance(R_p),charge transfer resistance(R_(ct))and CPT values,indicating the excellent MIC resistance of 2205-Cu DSS against the corrosive P.aeruginosa biofilm.The live/dead staining results and the SEM images of biofilm confirmed the strong antibacterial ability of 2205-Cu DSS.The largest pit depth of 2205-Cu DSS was considerably smaller than that of 2205 DSS after 14 d in the presence of P.aeruginosa(2.2μm vs 12.5μm).2205-Cu DSS possessed a superior MIC resistance to regular 2205 DSS in the presence of aerobic P.aeruginosa.