Search

Significant amounts of finely ground waste powder are produced during the heating process of silica-rich limestone aggregates in asphalt concrete plants. This resulting by-product poses challenges and opportunities in the scope of environmental sustainability, waste management, and resource utilization. Some attempts were made to utilize limestone powder in concrete production; however, its use was limited to a small quantity. Thus, this paper explores the feasibility of utilizing a high proportion of silica-rich waste limestone powder (LSP) in combination with ground granulated blast furnace slag (GGBS) and fly ash (FA) as precursor materials in producing alkali-activated mixtures. A series of experiments were conducted to evaluate the mechanical properties, durability characteristics, and microstructural analysis of the developed water-cured alkali-activated mortars and concrete. The results showed that the mixtures having a high volume of LSP (40%–50%) and GGBS/FA as precursor materials demonstrated adequate flowability (186–240 mm), satisfactory compressive strength (33–45 MPa), and good durability (water absorption was in the range of 2.6%–3.8%). In addition, the microstructural analysis in terms of scanning electron microscope (SEM), energy dispersive spectroscope (EDS), and Fourier transform infrared (FTIR) spectrometer revealed a dense microstructure with gel formation, which was correlated to mechanical strength. Finally, the environmental impact based on the life cycle assessment was evaluated, and the developed mixtures exhibited an average emission reduction of 63% compared with traditional concrete. The findings of this study suggest that waste LSP, typically disposed in landfills, can be effectively utilized up to 50% in the production of environmentally sustainable concrete. [ABSTRACT FROM AUTHOR]

This work studies the dispersion relations of wave propagation in infinite advanced functionally graded (FG) ceramic-metal plates. A simple integral hyperbolic higher-order shear deformation theory (HSDT), with undetermined integral terms and only four unknowns, is used to formulate a solution for the waves' dispersion relations. The effective functionally graded materials' (FGM) properties follow the power-law with three different types of uneven porosity distributions. The effect of foundation viscosity is investigated by considering the damping coefficient in addition to Winkler's and Pasternak's parameters. The wave propagation's governing equations are derived based on the present integral hyperbolic HSDT using Hamilton's principle. The eigenvalue problem describing the porous FG plate dispersion relations resting on a viscoelastic foundation is analytically determined. The theory accuracy is validated by numerically comparing the results with previously published works. Finally, the influences of gradation power, porosity parameters, and the viscoelastic foundation parameters on wave propagation in an FG plate are examined and discussed. [ABSTRACT FROM AUTHOR]

This work deals with the damping and vibration characteristics evaluation of sandwich beams based on higher-order shear deformation theories (HSDT's). The studied sandwich beams are composed of composite materials at faces and homogeneous, isotropic viscoelastic material in the core layer. This latter (viscoelastic material) is described by complex Young's modulus in the frequency domain. Indeed, the real part represents the stiffness, and the imaginary one describes the damping property. Nonlinear damping parameters and frequency curves are obtained using the nonlinear equation of frequency amplitude governed by multiple complex coefficients. In conjunction with a one-mode Galerkin's procedure, the harmonic balance method is employed to obtain the nonlinear loss factor and the response frequency curves. The nonlinear frequency value and, in turn, the system loss factor ratio are obtained for various amplitudes to examine the impacts of the ply angle of fiber-reinforced composite faces, the viscoelastic shear modulus, the shear deformation model, for considering different geometric and material parameters. In the framework of this study, one attempt is to describe a better way to achieve satisfactory passive vibration control of the laminated beams. [ABSTRACT FROM AUTHOR]

This study investigated the possibility of developing self-compacting concrete (SCC) utilising silicomanganese fume (SMF), an industrial waste material. SCC was produced by replacing cement with 10, 20, 30, 40, 50, 60, 70, 80 and 90% SMF. First, an assessment of the fresh properties of 10 SCC mixtures was carried out, and then mixtures satisfying the fresh requirements were selected for further evaluation. Plastic shrinkage and setting time of the fresh SMF-SCC mixtures were measured, and thereafter the mechanical properties and drying shrinkage were evaluated. The incorporation of SMF increased the dosage of superplasticizer required for a certain flow, but it enhanced the filling ability and passing ability of SCC. In addition, the incorporation of SMF increased the plastic and drying shrinkage, as well as initial and final setting times. Although there was an improvement in mechanical properties of SCC mixtures containing 10 and 20% SMF, increasing the quantity of SMF beyond 20% negatively affected the mechanical properties. Furthermore, the use of SMF decreased the cost of SCC by 7–42% and the CO2 emission decreased by 10–68%. [ABSTRACT FROM AUTHOR]

This paper reports the effects of key factors on the properties of geopolymer concrete mixtures containing 100, 90, and 85 mass% of natural pozzolan (NP) as primary and 0, 10, and 15 mass% of Portland cement as secondary cementitious materials. Two types of alkaline activators (NaOH and KOH), and three different sodium silicate (SS)/(NaOH or KOH) ratios of 1, 2, and 4 (by mass) were used. NaOH performed better than KOH in the development of compressive strength. While the strength increased with increase of silicate/alkali hydroxide ratio, a decrease in the strength was observed at a higher NP content. Results of the tensile strength, modulus of elasticity, shrinkage, thermal resistance, water absorption, acid resistance and SEM analysis tests conducted on selected mixtures also confirmed the beneficial effects of using a lower NP content activated by NaOH. An optimum mixture of geopolymer concrete, having a NP content of 85% and SS/NaOH ratio of 4.0, is recommended for the construction of structural members requiring high-performance concrete. [ABSTRACT FROM AUTHOR]

The reduction in service-life of reinforced concrete structures caused by corrosion of reinforcing steel is a major problem to the construction industry. The use of specialty steels is one of the strategies suggested to minimize this deterioration phenomenon. In this study, the corrosion-resistance of epoxy-coated and selected specialty steel bars embedded in concrete and exposed to chloride environment was evaluated. The specialty bars considered included two types of epoxy-coated bars with varying degrees of damage, stainless steel bars, stainless clad bars, and a low-carbon chromium steel bar. The corrosion resistance of the investigated reinforcing bars was investigated by measuring corrosion potentials and corrosion current density over a period of about 32 months. As expected, the corrosion resistance of specialty bars was better than that of the black (normal) bars. The corrosion resistance of the epoxy-coated bars decreased with the degree of surface damage. Further, the corrosion-resistance of epoxy-coated bars with up to 1% damage was better than that of the other specialty bars. Additionally, the low corrosion rate noted in the epoxy-coated bars suggests longer service-life of structures built with these bars compared to structures incorporating specialty steel bars considered in the study. The relatively low initial cost of epoxy-coated bars, compared to other specialty steel bars, and their longer life results in a considerable cost saving. Also, the decreased corrosion damage of concrete results in technical (long service-life and safety), environmental (aesthetics) and economic (less overall cost of construction) benefits. [ABSTRACT FROM AUTHOR]

This article presents the results of an experimental study conducted to assess the effect of sustained elevated temperature on the mechanical properties of ultrahigh performance concrete (UHPC). UHPC mixtures were prepared with four different dosages of polypropylene (PP) fibers, and each mixture was exposed to a sustained pre-spalling elevated temperature of 300°C for five durations. The experimental data indicate that the used PP fibers were effective in providing sufficient strength and ductility to UHPC mixtures at room temperature. However, the PP fibers ceased to function as reinforcement in UHPC specimens that were exposed to the elevated temperature for 60 minutes. With an increase in the exposure period after melting of the fibers, the specimens exhibited a brittle mode of failure accompanied with an enhancement in the compressive strength and compressive modulus of toughness and a reduction in the modulus of elasticity and flexural strength. The significance of two variables (exposure duration and fiber content) was evaluated, and correlations between the mechanical properties and selected parameters were obtained by conducting a statistical analysis of the experimental data. [ABSTRACT FROM AUTHOR]

This computational investigation focused on numerical modeling of the shear behavior of ultra‐high‐performance concrete (UHPC) beams reinforced longitudinally with high‐strength rebars and ordinary‐strength steel (stirrups). Nonlinear three‐dimensional finite element model, using the concrete damaged plasticity model and material properties obtained from uniaxial compressive and tensile laboratory tests, was conducted to simulate UHPC concrete beams within a commercial finite element software package ABAQUS 6.13. This investigation included the effects of various parameters; shear span‐to‐effective depth ratio (a/d), volume fraction of steel fibers, Vf, longitudinal reinforcement ratio, ρ, and stirrups spacing, s, on shear behavior of UHPC beams. Numerical results compared with previously obtained experimental results in terms of shear force–midspan deflection and cracking‐propagation behaviors. The results showed that finite element analysis predicted the shear behavior of UHPC beams in good agreement with the experimental data and predicted the response of the beam with variation in various parameters with a good accuracy. [ABSTRACT FROM AUTHOR]

This paper seeks to study and investigate the wave dispersion behavior in porous functionally graded (FG) carbon nanotube-reinforced composite (CNTRC) beams. The beams comprise four patterns of single-walled carbon nanotubes (SWCNTs) distributed in the polymer matrix. The mixture rule is used to estimate the CNTR beams’ material properties. Innovative to this study are three porosity models describing the porosity distributions within the matrix and a three-unknown integral higher-order shear deformation theory (HSDT) modeling analytically the CNTRC beams with a novel shape function expressing the distributions of shear stresses and strains. The equations of motion for CNTRC beams are derived based on Hamilton’s principle. The stiffness and mass matrices are formulated by a generalized solution of harmonic wave propagation to express the wave dispersion relations. Numerical comparisons with previously published works verify the applicability of this mathematical model. The paper studies the effects of CNTs patterns through the polymer matrix, porosity models, and volume fractions of the porosity and CNTs. Based on the analytical results, augmenting the porosity and CNTs volume fractions leads to faster phase and group velocities. Furthermore, the impact of CNTs volume fractions, porosity models, and porosity volume fractions becomes more pronounced as the wavenumber increases. [ABSTRACT FROM AUTHOR]