1,720,962 research outputs found
Studio e sperimentazione di sonde per il monitoraggio della corrosione delle armature in calcestruzzo
No full textRealizzazione e studio di una multisonda resistiva per il monitoraggio dell’umidità nel calcestruzzo
No full text
Effetto della carbonatazione sui prodotti passivanti dello zinco in soluzione satura di Ca(OH)2
No full textStudio dell’accoppiamento galvanico tra armature zincate e cassero metallico nel calcestruzzo fresco
No full textMetodo visivo per la misura dell'avanzamento del fronte di carbonatazione nel calcestruzzo
No full textIl brevetto propone un metodo innovativo per la prevenzione della corrosione delle armature in acciaio nel cemento armato. Il metodo classico di monitoraggio consiste nel prelevare campioni (carote) o realizzare campioni (provini) di calcestruzzo e misurarne lo spessore soggetto a carbonatazione in base all'interazione con una soluzione alcolica di fenolftaleina. La presente invenzione propone invece di utilizzare un metodo visivo per misurare il fronte di carbonatazione nel calcestruzzo senza impiegare carote, ottenendo risultati del tutto equivalenti a quelli ottenuti con questi elementi. Allo stesso tempo permette di ridurre al minimo il costo delle operazioni di monitoraggio e il danneggiamento per il carotaggio
Monitoring corrosion in concrete by means of Electrical Resistance Probes
No full textCarbonation and chlorides are the main reasons for deterioration of concrete, caused by
corrosion of rebars. Controlling the corrosion in concrete by means of a system able to
monitor corrosion’s parameters, such as potential, pH or corrosion rate, represents a
powerful way to prevent concrete deterioration and to reduce restoration’s cost of the
damaged structure. The aim of this work was to test Electrical Resistance Probes (ERP),
usually applied to corrosion measurements in pipelines or tanks, by embedding them in
concrete to monitor and estimate rebars corrosion rate. Five ERP probes were embedded into
two cylindrical concrete samples, together with four steel rebars. The samples were exposed
to chloride penetration and carbonation. Free corrosion potential and corrosion rate values of
the rebars were monitored, by means of corrosion resistance polarization measurements,
in comparison with the loss of metal provided by the ERP system. At first, samples were
submitted to accelerated exposition to the aggressive agents, then the exposition was carried
forward in “field” conditions and for long time. Comparing rebars corrosion rate with
respect to ERP data, the effectiveness of using this kind of probes in concrete was estimated.
ERP probes were able to register the start of corrosion with fair precision and good answer
quickness
Effect of carbonation process on the passivating products of zinc in Ca(OH)2 saturated solution
No full textThe effect of carbonation process on the passivating layer of zinc in Ca(OH)2
saturated solution was studied. The investigation was performed by means
of corrosion potential, corrosion current density, and impedance measurements.
To analyze the changes in the passivating layer, X-ray diffraction, Raman
spectroscopy and scanning electron microscopy (SEM) were utilized. The results
obtained indicate that the layer of calcium hydroxyzincate (Ca[Zn(OH)3]2 2H2O)
(CHZ), which determines the passivity state of zinc both in Ca(OH)2 saturated
solution and in concrete, is destroyed by the carbonation process, in agreement
with previous results obtained for galvanized steel embedded in concrete. X-ray
diffractometry and Raman spectroscopy showed that CHZ reaction with CO2
leads to the formation of Zn5(CO3)2(OH)6 (hydrozincite) and CaCO3 (calcite). SEM
observation confirms the deep transformation in the passivating layer caused by
carbonation. Corrosion potential and corrosion current density measurements
show that zinc maintains its passive state also after carbonation. However,
impedance measurements indicate that hydrozincite has lower passivating
properties than calcium hydroxyzincate in the carbonated solution
STUDIO DEGLI EFFETTI DELL’ACCOPPIAMENTO GALVANICO TRA ARMATURE ZINCATE E CASSERI METALLICI NEL CALCESTRUZZO FRESCO
No full textIn the present work, the phenomenon of hydrogen evolution on the surface of the
steel moulds, used to obtain concrete manufactured products reinforced with
galvanized rebars, has been investigated. The galvanic coupling between the moulds
and the galvanized reinforcements, in the fresh concrete just after the cast, leads to
a large amount of hydrogen bubbles evolution on the external surface of the
manufactured product, which will be characterized by a high roughness. In many
cases, it can be a problem for manufacturers of these products. In order to study this
phenomenon and to evaluate it quantitatively, a formwork in a reduced scale was
built for simulating a prefabricated real beam. It was equipped with a mould formed
by "segmented" steel walls of which, by means of an electric circuit suitably realized,
the partial currents and local potentials for each segment were measured.
Furthermore, the potential and the current of the macrocouple relative to the
galvanized bars were also monitored. From the electrochemical measurements and
the observations made on the surface of the manufactured product at the end of the
experimentation, it was found that the hydrogen evolution mainly affects the area of
the mould directly facing the galvanized bars, leading to a significant roughness of
the concrete surface in contact with this area
Effect of concrete carbonation process on the passivating products of galvanized steel reinforcements
No full textThe composition of passivating products on galvanized steel reinforcement in concrete during carbonation was studied. Cube-shaped concrete specimens were manufactured with Portland 52.5 R cement and reinforced with hot-dip galvanized steel sheets obtained from pure Zn and Zn-Sn-Bi-Ni alloy bath. The concrete specimens were exposed to air curing for 28 days and then to the carbonation chamber. Corrosion rate and potential measurements were performed both during the curing in air and exposure in a carbonation chamber. At defined periods of time, some concrete specimens were broken and the galvanized steel sheets were submitted to XRD, SEM observations and EDX analysis. The growth of the passivation products was evaluated by integrating the diffraction peaks. XRD analysis and SEM observations show that the layer of calcium hydroxyzincate (CaHZn), formed on the galvanized sheets during the air curing, is destroyed by the concrete carbonation process. However, potential measurements indicate that the galvanized steel always remains in the passive state. X-ray diffractometry was not able to identify the new passivating product; EDX maps suggest the presence of zinc carbonates
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