Papers by Tommaso Pastore
Materials
The topic of sustainability of reinforced concrete structures is strictly related with their dura... more The topic of sustainability of reinforced concrete structures is strictly related with their durability in aggressive environments. In particular, at equal environmental impact, the higher the durability of construction materials, the higher the sustainability. The present review deals with the possible strategies aimed at producing sustainable and durable reinforced concrete structures in different environments. It focuses on the design methodologies as well as the use of unconventional corrosion-resistant reinforcements, alternative binders to Portland cement, and innovative or traditional solutions for reinforced concrete protection and prevention against rebars corrosion such as corrosion inhibitors, coatings, self-healing techniques, and waterproofing aggregates. Analysis of the scientific literature highlights that there is no preferential way for the production of “green” concrete but that the sustainability of the building materials can only be achieved by implementing simul...
Sustainable development is a key factor in the modern building industry, which is mainly characte... more Sustainable development is a key factor in the modern building industry, which is mainly characterized by a severe consumption of raw materials. More specifically, the cement production process is characterized by a high carbon footprint, which has to be reduced in order to comply with the most recent international agreements regarding Greenhouse gas emissions. Nowadays, innovative binders can be produced by low temperature processes, which lead to lower CO2 emissions. However, such binders show different properties compared with ordinary portland cement (OPC), usually considered for structural reinforced elements. Owing to the different hydration products of the constituents during hardening – leading to low alkalinity of pore solution – their use in reinforced concrete structures has to be further investigated in order to evaluate the effects on durability and corrosion behaviour of steel reinforcing bars. The paper is devoted to the study of passive film formation on steel by mea...
The Ti6Al4V alloy is the most used to fabricate hip prostheses. Additive Manufacturing technology... more The Ti6Al4V alloy is the most used to fabricate hip prostheses. Additive Manufacturing technology (AM) leads to obtain parts with geometry reproducing the anatomical shape of the patient through reverse engineering techniques. Moreover, it allows to obtain rough surfaces, which favor the osseointegration. On the other hand, the technology and the post-processing heat treatment modify the alloy microstructure and the passive film, with consequent alteration of the passivity current. The ions released into the human body can lead to allergic reactions, inflammation and chronic intoxication. For this reason, it is important to know the speed of dissolution of the alloy in passive conditions. The aim of this work is to determine the passivity current of the alloy in simulated body solution at 38 °C by means of short (60 hours) and long (2500 hours) potentiostatic tests, obtaining the passivity current in equilibrium conditions.
The paper deals with the stress corrosion behavior of butt joints obtained by friction stir weldi... more The paper deals with the stress corrosion behavior of butt joints obtained by friction stir welding (FSW). The experimental study was performed on prismatic specimens obtained from FSWed joints of AA7075-T6 and AA2024-T3 alloy sheets having a thickness equal to 4 mm. The tests were executed on the same alloy (AA7075-AA7075 and AA2024-AA2024) and mixed joints (AA7075-AA2024). Tensile tests and four-point bending tests were carried out to evaluate the corrosion behavior and stress corrosion cracking susceptibility of FSW joints. During the tests, the electrochemical behavior of both the loaded (80% of the yield strength) and unloaded specimens in 3.5% NaCl solution was monitored by means of corrosion potential measurement, and electrochemical impedance spectroscopy (EIS). In the first hours of dipping, the EIS spectra of the loaded specimens of AA2024-T3 were different from the unloaded ones. After 24 hours, the electrochemical response became the same for all the specimens. This behavior was attributed to the formation of a thick layer of corrosion products that hindered the electrochemical couple within the specimens. After 1500 hours of immersion, the loaded specimens showed an intense intergranular attack which was not observed on the unloaded specimens. This stress enhanced intergranular attack was observed in the nugget of the welding, close to the continuous copper-rich precipitates at the recrystallized grain boundaries, induced by the thermo-mechanical action of the welding tool. These precipitates were formed of the coalescence of sub-micrometric precipitates present in the naturally aged base metal. Intergranular attacks were not observed in the heat-affected zone and on the base metals – where grain recrystallization did not occur. In these zones, the presence of sporadic shallow pits was only observed in correspondence of the large copper rich precipitates. The loaded specimens of AA7075-T6 showed EIS spectra different from the unloaded ones, in particular, the un-stressed specimens had three phase constants, whereas the stressed only two. The third phase constant at high frequencies disappears as the time of dipping increased, and the EIS spectra of all the specimens became similar. At the end of the tests, all the AA7075-T6 specimens – stressed and un-stressed - showed a very intense exfoliating attack started from the heat affected zone and propagated along the rolling direction. On the four-point bending specimens it was not possible to evidence the effect of the load on the morphology of the attacks. Finally, in the first hours of immersion, the EIS spectra of the AA7075-AA2024 welds showed EIS spectra similar to those of the AA2024-T3, increasing the dipping time, the EIS spectra became similar to the AA7075-T6 ones. Independently from the stress applied on these specimens, the corrosion morphology, was located only on the AA7075-T6 side. The complex behavior of the considered welds was also evidenced by means of local open circuit potential (LOCP) measurements: in fact, it was possible to observe the more active areas located in correspondence of heat affected zone. The differences in the LOCP can be attributed to the changing in the microstructure owing to the thermal mechanical action of the welding. The hardness along the welds showed a similar profile to the LOCP
The work studies the corrosion behavior of two aluminum alloys with different silicon content, Al... more The work studies the corrosion behavior of two aluminum alloys with different silicon content, AlSi7Mg and AlSi10Mg, produced by an additive manufacturing process based on Direct Metal Laser Sintering. The effect of subsequent thermal treatments at temperatures in the range 200 to 400 °C is considered. The resistance to selective attack was determined by immersion tests according to ISO 11846 on specimens obtained along two different orientations with respect to the main building direction. The results show the variations of the silicon particle morphology induced by heat treatments, affecting the alloy susceptibility to selective corrosion. The effect of silicon precipitates on alloy corrosion resistance and hardness is discussed.
The paper presents a general overview on typical corrosion phenomena of riveted metallic infrastr... more The paper presents a general overview on typical corrosion phenomena of riveted metallic infrastructures of historic importance. A significant example is analyzed, in relation to the morphologies of long-term degradation processes, with respect to the design of the structural elements, the peculiarities of the joining solutions, the selection of protection and maintenance systems.
The paper deals with the corrosion behavior of aluminum alloy AA 2024 T3 joined by means of frict... more The paper deals with the corrosion behavior of aluminum alloy AA 2024 T3 joined by means of friction stir welding (FSW). Electrochemical impedance spectroscopy (EIS) tests were carried out on four points bending specimens loaded at 80% of Yield Strength, in 35g/L sodium chloride solution. After exposure, the specimens were observed at the optical and scanning electron microscope (SEM) in order to assess corrosion morphologies. The EIS spectra show the initiation of the localized corrosion during first 24 hours of immersion. The modulus of the impedance modifies and a shift towards low frequencies of the bode-phase diagram was noticed over the time. A detrimental effect of FSW process on the corrosion behavior of the alloy due to microstructure modifications is confirmed, but the specimens did not show stress corrosion cracking. An intense intergranular attack was observed in the nugget of welding, close to continuous copper rich precipitates at the border of the recrystallized grain...
Semi-scale tests were performed with the aim of evaluating the influence on the resistance agains... more Semi-scale tests were performed with the aim of evaluating the influence on the resistance against SSCC of as-produced inner surface of steel pipes. The activity includes the design of tests on specimens sampled by preserving the inner surface of pipe and preliminary tests, which covers four samples taken from a commercial pipe. Two of the specimens were tested in as-produced surface conditions; the other two were heat treated in order to achieve 24 HRC hardness. Such value is above the minimum limit reported in ANSI/NACE MR0175/ISO15156-1, i.e. 22 HRC. The tests were performed in NACE solution saturated with H2S at 25°C and 1 bar.
Materials, 2021
Laser bed powder fusion (LPBF) is an additive manufacturing technology for the fabrication of sem... more Laser bed powder fusion (LPBF) is an additive manufacturing technology for the fabrication of semi-finished components directly from computer-aided design modelling, through melting and consolidation, layer upon layer, of a metallic powder, with a laser source. This manufacturing technique is particularly indicated for poor machinable alloys, such as Alloy 625. However, the unique microstructure generated could modify the resistance of the alloy to environment assisted cracking. The aim of this work was to analyze the stress corrosion cracking (SCC) and hydrogen embrittlement resistance behavior of Alloy 625 obtained by LPBF, both in as-built condition and after a standard heat treatment (grade 1). U-bend testing performed in boiling magnesium chloride at 155 and 170 °C confirmed the immunity of the alloy to SCC. However, slow strain rate tests in simulated ocean water on cathodically polarized specimens highlighted the possibility of the occurrence of hydrogen embrittlement in a sp...
Materials, 2020
The paper is devoted to the study of stress corrosion cracking phenomena in friction stir welding... more The paper is devoted to the study of stress corrosion cracking phenomena in friction stir welding AA-2024 T3 joints. Constant load (CL) cell and slow strain rate (SSR) tests were carried out in aerated NaCl 35 g/L solution. During the tests, open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) were measured in the different zones of the welding. The results evidenced initial practical nobilty of the nugget lower compared to both heat-affected zone and the base metal. This effect can be mainly ascribed to the aluminum matrix depletion in copper, which precipitates in form of copper-rich second phases. In this zones, no stress corrosion cracking was noticed, but well-evident stress-enhanced intergranular corrosion occurred. This is due to the uneven distribution of platic deformation during the slow strain rate tests. Higher strain values are localized at the heat affected zone, where softening occurs. On the contrary, stress values at the nugget are not suffi...
Metals, 2018
The presence of a conductive layers of hot-formed oxide on the surface of bars for pre or post-co... more The presence of a conductive layers of hot-formed oxide on the surface of bars for pre or post-compressing structures can promote localized attacks as a function of pH. The aggressive local environment in the occluded cells inside localized attacks has as consequence the possibility of initiation of stress corrosion cracking. In this paper, the stress corrosion cracking behavior of high strength steels proposed for tendons was studied by means of Constant Load (CL) tests and Slow Strain Rate (SSR) tests. Critical ranges of pH for cracking were verified. The promoting role of localized attack was confirmed. Further, electrochemical tests were performed on bars in as received surface conditions, in order to evaluate pitting initiation. The adverse effect of mill scale was recognized.
Journal of The Electrochemical Society, 2019
The aim of this work is to compare the corrosion resistance of nickel-base Alloy 625 (UNS N06625)... more The aim of this work is to compare the corrosion resistance of nickel-base Alloy 625 (UNS N06625) produced by laser powder bed fusion with that obtained via conventional casting and hot working. Cyclic potentiodynamic polarization and potentiostatic tests were performed in order to evaluate the corrosion resistance of the differently manufactured alloys according to ASTM G5, and in NaCl 0.6 M solution at pH 7 and pH 3, at 40°C. The electrochemical characterization was carried out on the as-produced alloy and after annealing at 980°C for 32 minutes (according to ASTM B446). This heat treatment was also performed on the commercial hot worked alloy. Two surface conditions, namely as-built and polished surfaces, were investigated on the additive manufactured specimens. The alloy produced by laser powder bed fusion was not susceptible to pitting in the considered environments and had a good localized corrosion resistance, slightly higher than that of traditional wrought material. However, as predicted, the corrosion resistance of the as-built surfaces increased after mechanical polishing. The correlation between the corrosion performance and microstructure is also discussed.
International Journal of Corrosion, 2016
The paper reports the results of an experimental work on the effect of steel microstructures on m... more The paper reports the results of an experimental work on the effect of steel microstructures on morphology and protectiveness of the corrosion scale formed in water saturated by supercritical CO2. Two HSLA steels were tested. The microstructures were modified by means of different heat treatments. Weight loss was measured after exposure at CO2partial pressure of 80 bar and 60°C temperature. The morphology of the scale was analyzed by means of scanning electron microscope (SEM) energy-dispersive X-ray spectroscopy (EDX). Cathodic potentiodynamic tests were carried out on precorroded specimens for evaluating the effect of preformed scales on cathodic polarization curves in CO2saturated sulphuric acid solution at pH 3, which is the value estimated for water saturated by supercritical CO2. The results are discussed in order to evaluate the effect of iron carbide network on scale growth and corrosion rate. Weight loss tests evidenced average corrosion rate values in the range 1–2.5 mm/y ...
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Papers by Tommaso Pastore