R. Romagnoli, R.O. Batic, V.F. Vetere, J.D. Sota, I.T. Lucchini and R.O. Carbonari
Hardened cement paste is a heterogeneous system resulting from the grouping of particles, films, microcrystals and other solid structural elements bounded in a porous mass. The…
Abstract
Hardened cement paste is a heterogeneous system resulting from the grouping of particles, films, microcrystals and other solid structural elements bounded in a porous mass. The cement paste microstructure must be understood firstly due to its influence on concrete properties. The behaviour of concrete greatly depends on the conformation of localised special structures rather than on general structures found in the mass cement paste. The objective of this paper was to study the cement paste microstructure, as a function of the water–cement ratio, in order to interpret the variations of the steel–mortar bond strength and the developing of the corrosion process in steel–mortar specimens kept in tap water and 3 percent sodium chloride solutions for 1 year. A description of the steel–mortar interface was also provided.
O.R. Batic, J.D. Sota, J.L. Fernández, N. Bellotti and R. Romagnoli
This research aims to study the influence of limestone filler on rebar corrosion.
Abstract
Purpose
This research aims to study the influence of limestone filler on rebar corrosion.
Design/methodology/approach
Mortar samples containing 35% calcareous filler and with a rebar inserted in the axis, were cast. Specimens were cured at the open air and during 28 days in lime water. After curing, they were submerged in two electrolytes (tap water and 3% NaCl) and corrosion parameters (corrosion potential and corrosion current) were monitored over time by d.c. techniques. Simultaneously, electrochemical noise measurements were carried out. After corrosion tests, rebars were pulled out by lateral compression, and their surface observed by scanning electron microscopy.
Findings
In general, carbonate additions impaired mortar protective properties, especially in the presence of chloride and changed the nature of the protective layer on rebars. The curing process did not introduce significant differences except for mortars with a high water cement ratio cured in lime water for which the beneficial effects of the simultaneous presence of carbonate and lime in the pore solution could be appreciated. The role of carbonate additions is to provide carbonate anions to passivate rebars. This passivation process caused corrosion rates not to be so high. Carbonate anions also deposited on oxide spots which were rendered passive but this process was not uniform. Certain areas on the rebar underwent intense carbonation while others showed increased corrosion rates.
Originality/value
There are not many corrosion studies about the influence of limestone filler on rebars corrosion. Particularly, this paper deals with mortars containing high percentages of carbonate additions. Results showed that the presence of this type of admixture changes the structure of the passive layer and, sometimes, may increase corrosion rates.
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Yingjun Zhang, Xue-Jun Cui, Yawei Shao, Yanqiu Wang, Guozhe Meng, Xiu-Zhou Lin, Dongquan Zhong and Dajian Wang
This paper aims to prepare a residual rust epoxy coating by adding different quantities of phytic acid (PA) on the surface of the rusty steel and investigate the corrosion…
Abstract
Purpose
This paper aims to prepare a residual rust epoxy coating by adding different quantities of phytic acid (PA) on the surface of the rusty steel and investigate the corrosion protection of PA and its action mechanisms.
Design/methodology/approach
A residual rust epoxy coating by adding different quantities of PA was prepared on the surface of the rusty steel. The influence of PA on the corrosion resistance of epoxy-coated rusty steel was investigated by means of electrochemical impedance spectroscopy and adhesion testing.
Findings
Results indicated that PA can substantially improve the corrosion resistance of epoxy-coated rusty steel. This improvement is due to the reaction of PA with residual rust and generation of new compounds with protection properties and increased adhesive strength effects on the coating/metal interface. The coating showed better protection performance when 2 per cent PA was added.
Originality/value
Considering the structure of the active groups, PA has strong chelating capability with many metal ions and can form stable complex compounds on the surface of a metal substrate, thereby improving corrosion resistance. In recent years, PA has been reported to be useful in the conversion of coatings or as green corrosion inhibitor. To the best of the authors’ knowledge, few studies have reported the use of PA as a rust converter or residual rust coating. The present work aims to improve the corrosion resistance of residual rust epoxy coating by adding PA.
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Rachna Jain, Amit Sharma, Manish Kumar Bhadu and Keshave Swarnkar
The aim of this study was to evaluate the corrosion inhibition efficiency of steel samples in different environments before and after the treatment with rust metamorphose (RM)…
Abstract
Purpose
The aim of this study was to evaluate the corrosion inhibition efficiency of steel samples in different environments before and after the treatment with rust metamorphose (RM), which is formulated in this research study and shows excellent adherence over the rusted surface of substrate because of the presence of the P-O-Fe bond.
Design/methodology/approach
An RM solution (phosphorylated polyphenol) was synthesised and characterised using Fourier transform infrared spectroscopy (FT-IR), and then the degree of protection offered by it to steel surfaces with and without the treatment with the RM solution in different atmospheres was evaluated;. Before and after treating with the RM solution, the corroded steel samples were characterised using X-ray diffraction (XRD), FT-IR, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The study of the passive behaviours of the corroded steel samples and RM-treated steel samples was done in different simulated atmospheres.
Findings
This RM solution is phosphorylated polyphenol solution (proved by FT-IR), which acts as a corrosion inhibitor on corroded steel surfaces because of the formation of a passive and symmetric adherent layer of phosphorylated polyphenol–iron complex (confirmed by FT-IR, XRD, EDS, SEM and adhesion X test). The significant improvement in corrosion resistance in splash conditions of 3.5 per cent NaCl, tap water and 1.5 per cent Na2SO4 was found with the treatment of phosphorylated polyphenol-based RM.
Originality/value
The development of RM and its characterisation with performance evaluation in different atmospheres is a novel approach in this research.
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Akshya K. Guin, M. Bhadu, Mahua Sinhababu, Ankita Mundhara, T.K. Rout and G. Udayabhanu
– The aim of this work was to study the effect of La(NO
Abstract
Purpose
The aim of this work was to study the effect of La(NO
3
)
3
on the corrosion behavior of sol-gel coating prepared by hydrolysis of 3-glycidoxypropyl)methyldiethoxysilane and 3-aminopropyltriethoxysilane. Generally, galvanized steel is subjected to a hexavalent chromium passivation treatment. Hexavalent chromium passivation is not an environment friendly product and researchers are looking for a suitable alternative for chromium passivation treatment. Some of the potential alternatives are silicate conversion coating or the use of silane-based coatings. In this context, sol-gel coating was investigated as a potential replacement for hazardous hexavalent chromium passivation treatment.
Design/methodology/approach
The sol-gel film was deposited on galvanized steel sheet by the dip coating method. The molecular vibration and chemical properties of sol-gel solution and coated films were obtained by infrared spectroscopy. Images from a scanning electron microscope were obtained to characterize the morphology of the film. The corrosion resistance of the coated samples was evaluated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves and salt spray tests.
Findings
The results indicated that La(NO
3
)
3
-doped coatings were more resistance to corrosion than undoped coating. The coating doped with 0.5 per cent La(NO
3
)
3
offered improved corrosion protection due to the inhibitive action of the La3+ ion.
Originality/value
This result can provide a reference for the development of chromium-free passivation for galvanized sheeting.
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Akshya Kumar Guin, Manish Bhadu, Mohua Sinhababu, Tapan Kumar Rout and G. Udayabhanu
This paper aims to investigate the potential of sol-gel coating as replacement for hazardous hexavalent chrome passivation treatment for galvanised iron (GI) sheet. Generally…
Abstract
Purpose
This paper aims to investigate the potential of sol-gel coating as replacement for hazardous hexavalent chrome passivation treatment for galvanised iron (GI) sheet. Generally, corrosion resistance properties of the GI sheet are increased by hexavalent chrome passivation treatment. But hexavalent chrome is hazardous and not environment friendly.
Design/methodology/approach
The aim of this study was to understand the effect of nano zinc oxide (ZnO) on corrosion behaviour of sol-gel coating prepared by hydrolysis of the 3-(Glycidoxy propyl) methyl diethoxy silane (GPTMS) and tetra-ethyl-orthosilicate (TEOS). The morphology of the film was characterised by a scanning electron microscope (SEM). The corrosion resistance of the coated samples was evaluated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarisation curve and salt spray test.
Findings
From a different corrosion resistance study, it has been observed that sol-gel coating doped with 1 per cent nano ZnO rendered maximum corrosion protection. Beyond 1 per cent of nano ZnO, corrosion resistance property of coated galvanised steel sheet decreased drastically which may be due to agglomeration of nano ZnO and high water permeability of coated galvanised steel sheet.
Research limitations/implications
The anti-corrosive property of the coating can be tested by means of atmospheric exposure which produces a real-time evaluation of the anti-corrosive nature of the coating under natural conditions rather than using an accelerated laboratory test.
Practical implications
It may be useful for other metal industry like aluminium. The work can be used as a guiding chemistry for development of chrome-free passivation for aluminium.
Social implications
It has the potential to replace hexavalent chrome passivation.
Originality/value
The use of nano ZnO in sol-gel polymer matrix for the development of corrosion resistant chrome-free polymer coating for galvanised steel sheet and its corrosion resistance study (EIS curve fitting, capacitance value and water permeability) is a novel approach in this research.
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EVERY librarian in his inmost heart dislikes newspapers. He regards them as bad literature; attractors of undesirable readers; a drain upon the limited resources of the library;…
Abstract
EVERY librarian in his inmost heart dislikes newspapers. He regards them as bad literature; attractors of undesirable readers; a drain upon the limited resources of the library; and a target against which the detractors of public libraries are constantly battering. From the standpoint of the librarian, newspapers are the most expensive and least productive articles stocked by a library, and their lavish provision is, perhaps, the most costly method of purchasing waste‐paper ever devised. Pressure of circumstances and local conditions combine, however, to muzzle the average librarian, and the consequence is that a perfectly honest and outspoken discussion of the newspaper question is very rarely seen. In these circumstances, an attempt to marshal the arguments for and against the newspaper, together with some account of a successful practical experiment at limitation, may prove interesting to readers of this magazine.