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In order to explore the corrosion resistance of duplex stainless steel under seawater corrosion and the compressive stiffness of its reinforced concrete columns, this study first performed seawater corrosion resistance tests on HRB400 ordinary steel rebar and S32205 duplex stainless steel rebar. The effect of the corrosion product film on the corrosion behavior was investigated through polarization curve tests and electrochemical impedance spectroscopy tests. The results showed that the corrosion rate of S32205 duplex stainless steel in a seawater environment was approximately 1/15 that of the HRB400 ordinary steel rebar. The anodic polarization curve of duplex stainless steel rebars exhibited a greater slope than that of carbon steel rebars. In the simulated seawater environment, the corrosion rate of these two kinds of steel bars showed different trends. The corrosion rate of ordinary steel bar HRB400 first decreased and then increased, while that of duplex stainless steel S2205 increased steadily. Furthermore, 18 short concrete columns reinforced with ordinary and duplex stainless steel rebars were subjected to the axial compression test and stiffness analysis; the stiffness of the short columns was calculated from the test data. The theoretical values agreed with the test values, with a stiffness calculation error of less than 5%. [ABSTRACT FROM AUTHOR]

Stainless steel has the characteristics of oxidation resistance, high temperature resistance, corrosion resistance, high strength, and high yield ratio. The use of stainless steel bars can extend the life of a structure, reduce later maintenance costs, and reduce the whole life cycle cost of the structure. In this paper, nine concrete columns reinforced with duplex stainless steel (S2205) (DSSRC) and nine ordinary reinforced concrete columns (ORC) were poured with the diameter of steel bars as the parameter, and axial compression tests were carried out on these eighteen concrete columns. The failure mode of the concrete columns is analyzed, and the compressive performance indexes of the two kinds of concrete columns are compared. The results show that, compared with the ORC, the cracking load of DSSRC is increased by 33%, the ultimate load is increased by 30.7%, and the deformation performance of the DSSRC is also improved significantly. On the basis of the test, the finite element model of DSSRC was established with the help of ABAQUS software, and the obtained failure law was consistent with the test; the experimental value, the calculated value, and the numerical simulation value of the axial compression capacity were in good agreement, which verified the feasibility of the test and provided a theoretical basis for practical engineering applications. [ABSTRACT FROM AUTHOR]

In order to obtain conductive concrete with good electrical conductivity and good mechanical properties, nanographite and magnetite sand excited by different activators and their combinations are added to ordinary concrete to obtain high quality and efficient conductive concrete. The optimal mixture ratio of alkali-excited conductive concrete and the effects of different activators and their combinations on the mechanics and electrical conductivity of concrete were studied. The microstructure of alkali-excited conductive concrete was analyzed by scanning electron microscope (SEM) to study its conductive mechanism. Results show that the conductive concrete obtained by compounding sodium hydroxide, sodium sulfate and calcium hydroxide has optimal mechanical and electrical properties when the graphite is 6% cement, and magnetite sand is 40% fine aggregate. The conductive concrete sample prepared by this method has a flexural strength of 6.84 MPa, a compressive strength of 47.79 MPa and a resistivity of 4805 Ω·cm (28 days). Compared with ordinary concrete (no nanographite and no magnetite sand), the compressive strength of conductive concrete is increased by 122.3%, the bending strength is increased by 116.5%, and the resistivity is reduced by 99.1%. SEM shows that the distribution of conductive materials in concrete is more uniform due to alkali excitation and calcium silicate hydrate (CSH) gel can be formed, which leads to better performance. The research in this paper is only a preliminary exploration of the characteristics of green conductive concrete, and the conductive heating characteristics and electromagnetic wave absorption properties of concrete, along with strength characteristics after adding conductive fillers, need to be further studied. It is suggested that further research should be carried out on the deicing characteristics of conductive concrete and the electromagnetic wave absorption properties used in stealth military engineering. [ABSTRACT FROM AUTHOR]

The bedrock used for underground construction has obvious traces of hydrodynamic scouring damage, and the mechanical properties of bedrock especially are severely damaged under a groundwater environment. On this basis, considering the excavated bedrock under various saturations, the uniaxial compression test of diorite is carried out. Meanwhile, scanning electron microscopy (SEM), electron energy spectroscopy (EDS) and X-ray diffraction (XRD) are used in the experiment. The variation law of the elastic p-wave velocity and microstructure and the response characteristics of the strength, deformation and mechanical parameters of rock under different flow rates and pH values are analyzed in detail. The results indicate that: (1) Saturations with a faster flow rate and lower pH value cause greater relative changes in the elastic longitudinal wave velocity of the samples. (2) The uniaxial compressive strength of the samples under various treatment conditions showed a decreasing trend. Compared with the dried samples, the uniaxial compressive strength of the samples under saturation with field flow rate v = 300 mm·s−1 and pH = 1 decreased by 46.08%, and the strength decreased by 35.67% under saturation with a field pH value = 6.56 and flow rate v = 900 mm·s−1. (3) The saturation with a stronger acidity, greater flow rate and longer action time causes the apparent dense structure of the diorite sample to be loose and accompanied by microcracks, which weakens its macromechanical properties. (4) Acid and hydrodynamic saturation produce water–rock chemical and physical effects on diorite, which weaken the connection force between mineral particles and the friction between fracture surfaces, reduce the elastic modulus, increase Poisson's ratio and accelerate the failure of diorite. [ABSTRACT FROM AUTHOR]

Waste glass (WG) is unsustainable due to its nonbiodegradable property. However, its main ingredient is silicon dioxide, which can be utilised as a supplementary cementitious material. Before reusing WG, the flexural strength (FS) and alkali–silica reaction (ASR) expansion of WG concrete are two essential properties that must be investigated. This study produced mortar containing activated glass powder using mechanical, chemical, and mechanical–chemical (combined) approaches. The results showed that mortar containing 30% WG powder using the combined method was optimal for improving the FS and mitigating the ASR expansion. The microstructure analysis was implemented to explore the activation effect on the glass powder and mortar. Moreover, a random forest (RF) model was proposed with hyperparameters tuned by beetle antennae search (BAS), aiming at predicting FS and ASR expansion precisely. A large database was established from the experimental results based on 549 samples prepared for the FS test and 183 samples produced for the expansion test. The BAS-RF model presented high correlation coefficients for both FS (0.9545) and ASR (0.9416) data sets, showing much higher accuracy than multiple linear regression and logistic regression. Finally, a sensitivity analysis was conducted to rank the variables based on importance. Apart from the curing time, the particle granularity and content of WG were demonstrated to be the most sensitive variable for FS and expansion, respectively. [ABSTRACT FROM AUTHOR]