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This research investigated the impact of substituting sand with graphite tailings (GT) on the chloride ion erosion resistance of recycled aggregate concrete (RAC). The role of GT is to significantly inhibit the penetration of chloride ions into the interior and slow down the corrosion process. However, the durability of graphite tailings recycled aggregate concrete (GTRAC) still depends on the replacement rate of recycled aggregate. At the same time, a multi-scale dynamic model of physical adsorption-chemical binding-free transport and erosion of chloride ions in GTRAC were established based on unsteady viscous fluid force and molecular dynamics. • The purpose of improve the sulfate attack performance of concrete by GT was proved. • The Proportioning design was optimized for improving the performance. • The mechanism of action of GT was discussed. • A multi-scale dynamic model was established in this paper. [ABSTRACT FROM AUTHOR]

Highlights • High cycle fatigue behaviors and chloride permeability of RC beams are investigated. • Chloride content at steel bar surface markedly increases at loading levels >0.3. • Fatigue loading level of 0.4, 0.45 combined with chloride corrosion reduce total fatigue life by at least 13%. Abstract High cycle fatigue behaviors (crack widths, deflections and fatigue life) and chloride permeability of RC beams were experimentally investigated. The experiment processes included initial fatigue loading followed by 3 months of NaCl solution wet-dry cycles without loading, and then fatigue life tests before chloride content measurement. The loading levels (ratio of the maximum fatigue loads over the ultimate static strength) and initial fatigue loading cycles are taken as parameters in this study. Results show that: (1) the fatigue behaviors of RC beams are greatly affected by the loading level and chloride corrosion, but they are rarely influenced by the initial fatigue loading cycles; (2) chloride content markedly increase when the loading levels exceed 0.3; (3) at the loading levels of 0.4 and 0.45, combined actions of initial fatigue damage and chloride corrosion cause at least 13% decrease of the total fatigue life; (4) initial fatigue loading cycles barely affect the residual fatigue life of RC beams when initial fatigue damage of RC beams are in the slow variation stage of damage development. [ABSTRACT FROM AUTHOR]

• Alkali-activated slag (AAS) mortar has better resistance to chloride ion corrosion. • Different cation types affect the D app of AAS mortar. • MIP and XRD was performed to show a decrease in porosity. • EIS was performed to show an inverse exponential relationship between R c,d and D app. This work focuses on evaluating the influence of four cationic chloride salts (NaCl, KCl, MgCl 2 and CaCl 2) on chloride ion diffusion characteristics of alkali-activated slag mortar. The chloride ion concentration profiles of alkali-activated slag mortar were tested in single cation and combined cation source solutions. The hydration products and mechanism of action were analyzed by XRD and MIP, and the chloride ion transmission characteristics of alkali-activated slag mortar were further analyzed in combination with EIS. The chloride ion apparent diffusion coefficient D app related to the chloride salt solutions with the four cation types decreases in the order of D app (KCl) > D app (NaCl) > D app (MgCl 2) > D app (CaCl 2). The combination of monovalent cations can promote the chloride ions diffusion of alkali-activated slag mortar, and the results of the combination of monovalent cations and divalent cations are different. The hydration products of slag are mainly C-S-H gels with low calcium to silicon ratio, which reacts with chloride salt to form Friedel's salt, which can fill the internal pores, optimize pore size distribution, and improve the resistance to chloride ion corrosion. [ABSTRACT FROM AUTHOR]

Corrosion and scaling of heat exchanger is a severe problem in oil refinery industries. In this paper, the corrosion mechanisms of tubes in the condenser at the top of the benzene tower have been investigated by elemental analyzer, optical microscopy, and scanning electron microscopy (SEM) with energy-dispersive spectrometry (EDS) and X-ray diffraction (XRD) analysis. It is concluded that corrosion occurred outside the tube due to a trace amount of acidic water containing chloride ion which condensed on the surface of tubes. Then the condensed acidic water led to electrochemical corrosion during heat exchanging process in the condenser at the top of the tower. Chloride ion plays a very important role in the tube corrosion. The most important point is that chloride ion could cause the depassivation of material. Moreover, chloride ion is easily absorbed onto the surface of tubes due to the negative charge. Later, the corrosion of tubes is accelerated due to ion migration if the concentration of chloride ion increases. In addition, the loose scales of corrosion product also accelerate the electrochemical corrosion since it makes the acidic aqueous solution easier to stay and concentrate on the tube surface. [ABSTRACT FROM AUTHOR]