No abstract

By considering the adverse environmental impacts of the cement manufacturing process, there have been many efforts for cement replacement by supplementary cementitious materials (SCMs), which can enhance the produced concrete performance while reducing cement consumption. This study evaluated the effects of various proportions of silica fume (SF), waste glass powder (WGP), and ground granulated blast furnace slag (GGBFS) on the mechanical and durability properties of concrete. The properties evaluated in this study include compressive, tensile, and flexural strength, magnesium sulfate and sulfuric acid attack, surface resistivity, rapid chloride penetrability test (RCPT), water absorption, depth of penetration of water, and microstructure analysis by scanning electron microscopy (SEM). The results of compressive, tensile, and flexural strength, chloride ion penetrability, and water absorption tests showed that adding 5% of SF to mixtures containing 10% WGP or 10% GGBFS improved concrete performance significantly due to packing density and synergistic effect; however, adding 5% of SF to concrete mixtures decreased the resistance against the magnesium sulfate and sulfuric acid attack. The binary mixture of 15% of WGP showed appropriate performance against the magnesium sulfate and sulfuric acid attack, which may be due to the sacrificial nature of WGP. In addition, the binary mixtures of 15% of WGP and 15% of GGBFS reduced the depth of penetration of water by 45%. Microstructure analysis by SEM showed that the presence of SF, along with WGP and GGBFS, improves the packing density. Finally, adding 5% of SF is suggested to improve the properties of concrete mixtures containing WGP and GGBFS.

This paper presents an approximate multicontact model to study dynamic bond stress-slip based on the concrete damage-plastic model. To establish the bond stress-slip between rebar and concrete, an elastic-plastic steel cylinder contact element was used as the tube (ring contact element), and then, by reducing the bond strength, the amount of slip between rebar and concrete and its effect on concrete damage-plastic parameters were considered. When concrete cracks, the parameters of concrete cracking, the plasticity of rebar and concrete fracture, and the pull-out of rebar from concrete are used to consider the bond-slip relationship between rebar and concrete. Meanwhile, an external constraint in the cylinder model is taken into account. The bond strength calculated by the presented model is compared with the pull-out test specimen results, and the errors are generally within 15%. Finally, using the results obtained from the amount of slip in models, an approximate mathematical relationship between the slip of the rebar inside the concrete can be obtained in terms of the resistance of the ring contact element (instead of the concrete surrounding). This formula can be used to calculate the bond-slip rate of all the rebars of a structure. The results of the mentioned model using the ABAQUS software demonstrated that by reducing the strength of the ring contact element by 20%, slip increased by 4.2%. Also, with an 80% reduction in ring strength, the bond-slip rate increases by 45%. The proposed approximate relationship has reasonable accuracy and lower computational cost.

The current work aimed to fabricate a new cocaine sensor of octahedral palladium-doped cobaltite composite (Oh-Pd 2 + : Co 3 O 4 -C) using a simple hydrothermal protocol. As-fabricated cocaine sensing approach was validated by various methods. Energy dispersive X-ray analysis, X-ray diffraction and scanning electron microscopy were recruited to characterize our charged modified composite. The electrode could sensitively detect cocaine, with a lengthy linear range (0.01 μM-900.0 μM) and a limit of detection (1.3 nM). The quantitative cocaine determination was achieved in the biological specimens using our modified electrode, the results of which displayed admirable outcomes.