This study analyzes the microstructure and strength properties of high-strength concrete containing electric-arc-furnace oxidizing slag (ES). Thus, three different water-to-binder ratios and four different ES-replacement ratios were considered while evaluating the hydration products of the specimens, their porosity, pore-size distribution, and compressive and splitting tensile strengths, depending on the curing age. According to the x-ray diffraction (XRD) patterns, the ES specimens of both portlandite and hatrurite exhibited higher peak intensities than those of the plain specimen (High-strength concrete, i.e., HSC). Further, from the results of the mercury intrusion porosimetry (MIP) test, it was observed that the cumulative pore volume of the ES specimens was higher than that of the HSC. Also, the porosity of the ES specimen, whose ES-replacement ratio was 20%, was approximately 37.9% higher than that of the HSC. The compressive strength and splitting tensile strength of the ES specimens significantly decreased when the ES-replacement ratio was 20%, while the best self-sensing properties were exhibited. From all the experiments, it was observed that an ES-replacement ratio of 15% exhibited similar microstructure and strength properties to those of the HSC.
In this study, experimental tests were performed to determine the electromagnetic shielding characteristics of reinforced concrete based on the thickness of concrete and rebar. In addition, the electromagnetic shielding characteristics based on the steel-fiber volume ratio and rebar spacing of fiber-reinforced concrete were evaluated. Concrete showed significant Shielding Effectiveness (SE) in a high-frequency band with increasing thickness, but the rebar exhibited significant SE in the low-frequency band with increasing diameter, decreasing rebar spacing, and increasing layer. The SE increased with the steel fiber volume ratio, and it also increased owing to the decrease in the rebar spacing for 1.5 vol.% steel fibers.
In this study, basic data were used to quantitatively determine the initial properties of self-consolidating lightweight concrete by analyzing various characteristics, such as air content, workability, segregation resistance, filling capacity, air/dry density, and strength according to the incorporating ratio of lightweight aggregate. With the exception of Mixture (LF75-LC100) that uses 100% lightweight coarse aggregate (LC) and 75% lightweight fine aggregate (LF), all the mixtures satisfied the performance criteria for workability, segregation resistance, and filling capacity, as suggested in the JSCE, and air/dry density, as suggested in the Concrete Standard Specification. The compressive strength of all the variables, except the LF75-LC100, was measured to be at least 50 MPa, but the strength decreased in a manner similar to that depicted in previous research when LC was incorporated. The results of the above experiments indicated that 100% of the LC and 50% of the LF was the optimal mix for self-consolidating lightweight concrete.
There is increased interest in applying electromagnetic (EM) shielding to prevent EM interference, which destroys electronic circuits. The EM shielding’s performance is closely related to the electrical conductivity and can be improved by incorporating conductive materials. The weight of a structure can be reduced by incorporating lightweight aggregates and replacing the steel rebars with CFRP rebars. In this study, the effects of lightweight coarse aggregate and CFRP rebars on the mechanical and electrical characteristics of concrete were investigated, considering the steel fibers’ incorporation. The lightweight coarse aggregates decreased the density and strength of concrete and increased the electrical conductivity of the concrete, owing to its metallic contents. The steel fibers further increased the electrical conductivity of the lightweight aggregate concrete. These components improved the EM shielding performance, and the steel fibers showed the best performance by increasing shielding effectiveness by at least 23 dB. The CFRP rebars behaved similarly to steel rebars because of their carbon fiber content. When no steel fiber was mixed, the shielding effectiveness increased by approximately 2.8 times with reduced spacing of CFRP rebars. This study demonstrates that lightweight aggregate concrete reinforced with steel fibers exhibits superior mechanical and electrical characteristics for concrete and construction industries.
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