Evaluation of Technical Feasibility of Reusing Coal Ash in Dense Asphalt Mixes by Assessing Mechanical Performance.

This manuscript evaluates the technical feasibility of reusing coal ash in the formulation design of dense asphalt mixes. Physicochemical and mineralogical properties of fly and bottom ash matrixes prepared with coal ash were analyzed by scanning electron microscopy (SEM), X-Ray diffraction (XRD), semi-quantitative spectrometry by X-Ray fluorescence (XRF) and surface characterization by Nitrogen (N2) adsorption. Filler fractions under 0.075 mm with 6.0% in weight from an entirely gneissic aggregate gradation curve taken as reference were compared to identical mixes prepared with fly and bottom ashes individually and also to a combined sample with 3.0% of each ash type. Tests on compaction ability with gyratory shear press, resistance to action of water and to rutting were carried out to compare mechanical performance. The results indicate that both gneissic and coal ash fillers do not form dipoles of effective electric attractions to bituminous matrixes, resulting in inert and hydrophilic behavior regarding to action of water, respectively. Despite surface and morphologic characteristics underlying the mechanical performance of gneissic fillers, coal ash matrixes have shown, in general, good technical feasibility to be used in asphalt mixes.

Tribo-mechanical characterization of rough, porous and bioactive Ti anodic layers.

Rough and porous titanium oxide layers, which are important features for improving the osseointegration of Ti implants with bone tissues, are obtained through the technique of anodic oxidation. The thicknesses of such coatings are typically in the order of micrometers, and their mechanical characterization can be assessed by instrumented indentation, provided that the composite nature of the surface is considered. Titania anodic layers were produced on Ti under galvanostatic mode using Ca-P-based electrolytes (a mixture of (CH3COO)2Ca⋅H2O and NaH2PO(4)⋅2H2O), employing current densities (J) of 150 mA/cm2 and 300 mA/cm2. The structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy with electron dispersive X-ray spectroscopy (SEM/EDS), and profilometry, and the chemical features were characterized by X-ray photoelectron spectroscopy (XPS). TiO2 layers presented the crystalline phases rutile and anatase, and incorporation of Ca and P presented as a calcium phosphate compound. The porosity, roughness, and thickness increased with J. Analytical methods were employed to obtain the modified layers' elastic modulus and hardness from instrumented indentation data, deducting the substrate and roughness effects. The elastic moduli were about 40 GPa for both values of J, which are similar to the values for human bones (10-40 GPa). The hardness decreased with indentation load, varying from 5 GPa at the near surface to 1 GPa at the layer-substrate interface. Such hardness behavior is a consequence of the surface brittleness under normal loading. Additional scratch tests using an acute tip indicated that the layer integrity under shear forces was 220 mN (J=150 mA/cm2) and 280 mN (J=300 mA/cm2). TiO2 layers produced with both current densities presented good results for in vitro bioactivity tests using simulated body fluid (SBF) solution, which can be attributed to a combined effect of the microstructure, layer porosity, and hydroxyl radicals in plenty at the near surface.

Effect of adsorbed/intercalated anionic dyes into the mechanical properties of PVA: layered zinc hydroxide nitrate nanocomposites.

Zinc hydroxide nitrate (ZHN) was adsorbed with anions of blue dyes (Chicago sky blue, CSB; Evans blue, EB; and Niagara blue, NB) and intercalated with anions of orange dyes (Orange G, OG; Orange II, OII; methyl orange, MO). Transparent, homogeneous and colored nanocomposite films were obtained by casting after dispersing the pigments (dye-intercalated/adsorbed into LHSs) into commercial poly(vinyl alcohol) (PVA). The films were characterized by XRD, UV-Vis spectroscopy, and mechanical testing. The mechanical properties of the PVA compounded with the dye-intercalated/adsorbed ZHN were evaluated, and reasonable increases in Young's modulus and ultimate tensile strength were observed, depending on the amount and choice of layered filler. These results demonstrate the possibility of using a new class of layered hydroxide salts intercalated and adsorbed with anionic dyes to prepare multifunctional polymer nanocomposite materials.

Hardness and elastic modulus of TiO2 anodic films measured by instrumented indentation.

The aim of this work was to investigate the mechanical properties of the titanium anodic films (TiO2) produced by anodic oxidation under galvanostatic conditions, using a 1.4M phosphoric acid electrolyte, with different current densities (J) on commercially pure titanium (cp-Ti). The morphology of the oxide films were observed by scanning electron microscopy (SEM), whereas the composition of the film was determined by Raman spectroscopy. Porosity, average roughness (Ra) and thickness of the TiO2 films increased with the applied J. Hardness and elastic modulus were measured by instrumented indentation technique, and the influence of the substrate was corrected using analytical models. The anodic films presented higher hardness and lower elastic modulus values compared with the cp-Ti.