René Croche

In the aeronautics industry, high-strength steels such as AerMet 100 and 4340 are widely used in critical structural components that must withstand extreme operating environments. These materials possess high tensile strength, fracture toughness, and fatigue resistance. The aim of this investigation is to study the susceptibility to localized pitting corrosion of two aeronautics alloys, AerMet 100 and 4340, and their immersion in H₂SO₄, NaCl, and HCl solutions at room temperature, using electrochemical noise (EN) according to the ASTM ASTM-G199 standard. The EN signal was filtered by two different methods, and the polynomial method was employed to obtain Rn, LI, Kurtosis, Skewness, and the potential spectral density analysis (PSD). Results indicate that AerMet 100 exhibits lower corrosion rate—up to an order of magnitude lower than 4340. The resistance noise of 1599 Ω·cm² in NaCl is higher. This same behavior is replicated when analyzing the noise impedance response (Z_n). In conjunction with the analyses of PSD slope, it is reported that localized corrosion is the predominant mechanism in the evaluated environments.

In the present investigation, the physical, mechanical and durability properties of six concrete mixtures were evaluated, one of conventional concrete (CC) with 100% Portland cement (PC) and five mixtures of Ecofriendly Ternary Concrete (ETC) made with partial replacement of Portland Cement by combinations of sugar cane bagasse ash (SCBA) and silica fume (SF) at percentages of 10, 20, 30, 40 and 50%. The physical properties of slump, temperature, and unit weight were determined, as well as compressive strength, rebound number, and electrical resistivity as a durability parameter. All tests were carried out according to the ASTM and ONNCCE standards. The obtained results show that the physical properties of ETC concretes are very similar to those of conventional concrete, complying with the corresponding regulations. Compressive strength results of all ETC mixtures showed favorable performances, increasing with aging, presenting values similar to CC at 90 days and greater values at 180 days in the ETC-20 and ETC-30 mixtures. Electrical resistivity results indicated that the five ETC mixtures performed better than conventional concrete throughout the entire monitoring period, increasing in durability almost proportionally to the percentage of substitution of Portland cement by the SCBA–SF combination; the ETC mixture made with 40% replacement had the highest resistivity value, which represents the longest durability. The present electrical resistivity indicates that the durability of the five ETC concretes was greater than conventional concrete. The results show that it is feasible to use ETC, because it meets the standards of quality, mechanical resistance and durability, and offers a very significant and beneficial contribution to the environment due to the use of agro-industrial and industrial waste as partial substitutes up to 50% of CPC, which contributes to reduction in CO₂ emissions due to the production of Portland cement, responsible for 8% of total emissions worldwide.

Novel green concrete (GC) admixtures containing 50% and 100% recycled coarse aggregate (RCA) were manufactured according to the ACI 211.1 standard. The GC samples were reinforced with AISI 1080 carbon steel and AISI 304 stainless steel. Concrete samples were exposed to 3.5 wt.% Na₂SO₄ and control (DI-water) solutions. Electrochemical testing was assessed by corrosion potential (E_corr) according to the ASTM C-876-15 standard and a linear polarization resistance (LPR) technique following ASTM G59-14. The compressive strength of the fully substituted GC decreased 51.5% compared to the control sample. Improved corrosion behavior was found for the specimens reinforced with AISI 304 SS; the corrosion current density (i_corr) values of the fully substituted GC were found to be 0.01894 µA/cm² after Day 364, a value associated with negligible corrosion. The 50% RCA specimen shows good corrosion behavior as well as a reduction in environmental impact. Although having lower mechanical properties, a less dense concrete matrix and high permeability, RCA green concrete presents an improved corrosion behavior thus being a promising approach to the higher pollutant conventional aggregates.

In this study, ternary ecological concrete (TEC) mixtures were produced with partial substitution of the ordinary Portland cement (OPC) by 10%, 20%, and 30% of sugar cane bagasse ash (SCBA) and silica fume (SF); a control mixture (100% OPC) was prepared according to ACI 211.1 standard. The studied TEC specimens were reinforced with AISI 304 stainless steel and AISI 1018 carbon steel rebars. TEC reinforced specimens were immersed in two different electrolytes, a control (DI-water) and 3.5 wt.% MgSO₄ solution, for 180 days. The electrochemical corrosion was monitored by corrosion potential (E_corr) according to ASTM C-876-15 standard, and the linear polarization resistance (LPR) technique using ASTM G59 standard. The E_corr and current density i_corr results show that AISI 304 stainless steel rebars have a high corrosion resistance, with i_corr values below 0.1 µA/cm², which is interpreted as a level of negligible corrosion. The best corrosion performance was found for the TEC mixture made with a 20% addition of blend of sugar cane bagasse ash-silica fume (SCBA-SF) to the OPC.