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Coal-bearing metakaolin (CMK) is a highly active volcanic material. In this study, the compressive strength of CMK cement soil was tested, along with five CMK samples cured in different concentrations of Na2SO4 solution. The compressive strength of the CMK cement soil first increased and then decreased with increasing Na2SO4 concentrations. When the Na2SO4 solution concentration was 18 g/L, the compressive strength of the CMK cement soil reached its maximum value. Additionally, X-ray diffraction (XRD) analysis of the chemical reactions between the CMK cement soil and Na2SO4 solution and scanning electron microscopy (SEM) were used to analyze the phase composition and microstructure of the CMK cement soil, respectively. Thus, the pore distribution of the CMK cement soil could be calculated and classified from a 500x magnification SEM image using Image-ProPlus6.0 analysis software. This study explains the mechanism of curing CMK cement soil in a Na2SO4 solution based on its phase analysis, microstructure, and pore distribution. [ABSTRACT FROM AUTHOR]

The results of this research on the electrochemical behavior of Cu24Zn5Al alloy in a 0.1 mol/dm3 sodium sulfate (Na2SO4) solution containing 1-phenyl-5-mercaptotetrazole (PMT) are presented in this paper. The influence of PMT concentration, chloride ion concentration, and pre-treatment were examined. The influence of pre-treatment was studied in terms of the effect of the immersion time of the electrode in the appropriate inhibitor solution. After selecting the optimal immersion time, its effect on the behavior of the Cu24Zn5Al alloy was tested in a 0.1 mol/dm3 solution of sodium sulfate in the presence of different concentrations of chloride ions. Research shown that with the increase of PMT concentration, the anodic current density around the corrosion potential decreases, indicating that PMT behaves as a corrosion inhibitor for Cu24Zn5Al alloy. [ABSTRACT FROM AUTHOR]

[Display omitted] • CSH models with different Ca/Si ratios were constructed. • The simulation duration of 40 ns ensures data reliability. • The dynamic process of Ca ions dissolution was studied. • The potential mechanism of Ca/Si on Ca ions dissolution was revealed. The decalcification behavior of calcium silicate hydrate (CSH) under sulfate attack poses a critical challenge to the long-term durability of cement-based infrastructure, yet understanding its underlying microscopic mechanisms remains elusive. This study employs molecular dynamics to compare the differences in calcium ion dissolution capability of CSH substrates with varying Ca/Si ratios under sulfate solution exposure. The results show that the dissolution amount and dissolution efficiency of Ca are positively correlated with Ca/Si, and the root cause depends on the basic structure of CSH. With the increase of Ca/Si, the electronegativity of CSH decreases, and the adsorption capacity and stability of cations weaken. Meanwhile, Ca ions are less limited by the silicate chain coordination, water molecules are more likely to invade the substrate interior and replace the Ca ions. This research aims to provide a molecular basis for cement production and durability applications in marine engineering. [ABSTRACT FROM AUTHOR]

The results of this research on the electrochemical behavior of Cu24Zn5Al alloy in a 0.1 mol/dm3 sodium sulfate (Na2SO4) solution containing 1-phenyl-5-mercaptotetrazole (PMT) are presented in this paper. The influence of PMT concentration, chloride ion concentration, and pre-treatment were examined. The influence of pre-treatment was studied in terms of the effect of the immersion time of the electrode in the appropriate inhibitor solution. After selecting the optimal immersion time, its effect on the behavior of the Cu24Zn5Al alloy was tested in a 0.1 mol/dm3 solution of sodium sulfate in the presence of different concentrations of chloride ions. Research shown that with the increase of PMT concentration, the anodic current density around the corrosion potential decreases, indicating that PMT behaves as a corrosion inhibitor for Cu24Zn5Al alloy.

An experimental investigation was conducted to investigate the performance of geopolymers made with three different precursors consisting of fly ash, Ground Glass Fiber (GGF), and Glass-Powder (GLP) exposed to sodium sulfate solution. Precursors were activated using either sodium hydroxide solution or combinations of sodium hydroxide and sodium silicate solution with varying levels of sodium and silica content. Among the mixtures with each of the three precursors, mortar mixtures with the highest compressive strength were selected to test their resistance against exposure to a 5% sodium sulfate solution. Changes in the weight and compressive strength of the specimens were monitored up to 120 days of exposure. In addition, change in the microstructure of geopolymer samples and mineral phases was investigated using SEM-EDX and XRD analyses, respectively. Further, techniques such as mercury intrusion porosimetry (MIP) spectrometry and inductively coupled plasma mass spectrometry (ICP-MS) were used to study the pore structure and the leachability of elements from geopolymers, respectively. Results of this study revealed that the GGF and fly ash-based geopolymers performed significantly better in comparison to the GLP-based geopolymer, when exposed to the sodium sulfate solution. The durability of GGF and Fly ash based geopolymer samples could be related to their stable alumino-silicate gel that develops upon geopolymerisation as well as the low amount of calcium oxide in the geopolymer systems. On the other hand, the poor performance of the GLP-based geopolymer could be related to the less stable geopolymerisation products which result in increased porosity, and the high amount of available alkalis present in the raw GLP. [ABSTRACT FROM AUTHOR]

The potentiodynamic polarization test and slow strain rate tensile test were carried out in 3.5 wt.% NaSO solution with different pH values (2, 7, and 12). It was found that the SCC susceptibility of AZ31 magnesium alloy in 3.5 wt.% NaSO solution was deteriorated significantly with the decreasing pH. This was consistent with the electrochemical properties. There were filiform corrosion forms on the specimen surface after slow strain rate tensile test in 3.5 wt.% NaSO solution, which indicated the characteristics of general corrosion. Moreover, there were multiple stress corrosion crack initiation sources. The SCC fracture of AZ31 magnesium alloy in air was a mix type, while it was cleavage fracture in 3.5 wt.% NaSO solution. [ABSTRACT FROM AUTHOR]

• With the increase of erosion time and concentration, the changes law of apparent morphology, relative mass and ultrasonic wave velocity of RPC were revealed. • The variation law of compressive strength of RPC under different concentration erosion was revealed. • The variation law of compressive strength with the change of relative mass and ultrasonic wave velocity was revealed. • The erosion deterioration mechanism of RPC was revealed. With the development of economy, the global waste plastics are gradually increasing. Adding recycled particles of waste plastics to concrete materials can effectively recover waste plastics, but it will also have an impact on the sodium sulfate resistanceperformance of concrete.In this work, at the macro level, the three concentrations (3%, 5%, and 7%)sodium sulfate resistance of recycled plastic concrete (RPC)andnormalconcrete (NC) were analyzed and evaluated from its appearance, relative mass, compressive strength, andultrasonic wave velocity. From the microscopic aspect, the microstructure and phase composition at 5% erosion concentration were tested and analyzed by SEM, XRD, and FT-IR.The deterioration mechanism of RPC eroded by sodium sulfate solution was analyzed.Results showed thatthe effect of sodium sulfate solution on RPC is similar to that of NC in the early stage. In the later stage of erosion, the erosion degree of RPC is less than that of NC. The deterioration characteristics of RPCwere mainly the development process of corners, edges, and then surface, and the rate of mass increase and ultrasonic wave velocity decrease gradually increasedwith the increase of erosion concentration and erosion time.Under 3% and 5% concentration erosion, the variation range of compressive strength was lower than that of normal concrete in the whole erosion stage, and under 7%concentration erosion, it showed the opposite effects.The compressive strength increased first and then decreased with the increase of mass change rate and the decrease of ultrasonic wave velocity.Taking the compressive strength as the damage parameter, the damage degree model of recycled plastic concrete eroded by sodium sulfate solution was deduced.The erosion deterioration mechanism of RPC was revealed by microstructure and phase analysis. [ABSTRACT FROM AUTHOR]