Key Engineering Materials Vol. 841

Abstract: . Banks of stone materials from Michoacán, Mexico were characterized, since they are used in the construction of infrastructure in the area. With these materials are made hydraulic concrete mixtures or asphalt mixtures, foundations, paving stones and in restoration of historical monuments. The rocks analyzed and characterized, come from banks of volcanic stone materials and banks of crushed stone materials, which were subjected to mechanical tests such as uniaxial compression resistance (UCR), in addition was used scanning electron microscope (SEM), by means of which the characterization was carried out, obtaining morphological information of the material. The comparison of physical-mechanical properties with the elements they possess is important to estimate their behavior within ceramic matrices or as a structural element.

Abstract: The use of better materials is essential for the development of a country, that is why in this work we analyze a mixture of cement-based mortar with an addition of mucilage from a plant called Maralfalfa, said plant is used as feed for cattle and it is thought that its hydrate content can improve the water-cement reaction. Two mixtures were made, one control and another with the addition. The material used was: volcanic sand from Michoacán, cement CPC 30R RS, drinking water and the addition of mucilage. Cubic specimens (5x5x5 cm), prismatic specimens (4x4x16 cm) and briquettes were made, which were tested at 7, 14, 21, 28, 45 and 70 days of age. The tests performed were non-destructive (density, ultrasonic pulse rate and electrical resistivity) and destructive (simple compression, flexion and tension). The density results indicate that the mixture with addition densifies the cement matrix, the ultrasonic pulse velocity results are very similar between the mixtures, the results of electrical resistivity indicate that the control mixture is slightly higher. In terms of simple compression and flexion, it is indicated that the mixture with the addition was higher than the control, whereas the voltage results indicate the opposite. In addition, it was found that the addition retards the setting time of the mixture.

Abstract: The porous nanostructured hydroxyapatite (HA) has the high specific surface area and loading capacity that is useful for enhancing bioactivity, sinterability, densification, and the capacity for loading the drug, protein, heavy metals, etc. For the first time, the bipolar membrane in electrochemical method was developed for the synthesis of hydroxyapatite nanosheet-assembled porous structures. The bipolar membrane was installed in the electrolysis cell to separate the cell into two chambers. The bipolar membrane prevented the OH^- ions to move away from the cathode chamber and the H+ ions to go to the cathode chamber. In this condition, HA was formed in the cathode chamber while the other calcium phosphate was formed in the anode chamber. The pH increase of solution rapidly leads to more effective the formation of the nanostructured HA. The higher the electrolysis time and the current density the greater the tendency of nanostructured HA formation. The mechanism of HA hydroxyapatite nanosheet-assembled porous structures formation includes the agglomeration formation of the spherical-like particles, the formation of agglomeration nanosheet structures, and the formation of HA hydroxyapatite nanosheet-assembled porous structures.

Abstract: The paper investigates experimentally the usability of ultra-high-strength stainless steel and abrasion resistant steel in laser-welded sandwich structures. The fatigue and shear strength of laser joints were investigated using lap joints that were welded using two very different energy inputs. Also the effect of multiple weld tracks was investigated. The properties of separate laser welds were characterized by hardness testing and optical microscopy. Results of the hardness measurements showed that there was softened area at heat-affected-zone and weld metal of the ultra-high-strength stainless steel welds. AR steels weld metal was harder than base metal and there was softened zone in heat-affected-zone of the weld. The shear strength of tested single weld joints of the ultra-high-strength stainless steel was higher compared abrasion resistant steel single weld joints, but stronger joint can be made with multiple weld seams for abrasion resistant steel. Fatigue strength of investigated ultra-high-strength stainless steel lap joint was lower than fatigue strength of abrasion resistant steel lap joint in the low-cycle regime, but there was no practical difference in fatigue limit (10e7 cycles).

Abstract: This study also investigates the effectiveness of multiple surface modification of recycled concrete aggregate (RCA) with respect to mechanical properties of the resultant recycled aggregate concrete (RAC) when exposed to various curing conditions, namely, normal water (N_w) and seawater (S_w). The properties included compressive and flexural strength and impact resistance. Findings show that effect inclusion of the treated coarse RCA is significant in enhancing the mechanical properties of RAC. The exposure to S_w appears to affect the degradation of the compressive strength of RAC remarkably in a marine environment. In this case, however, using of treated RCA is found beneficial in decreasing the deterioration in the compressive strength of RAC.

Abstract: Damage or failure frequently occurs on gearbox gears. If this occurs in the gearbox of tractors, this can be severe. This study aimed to determine the cause of the spur gear fracture through empirical and simulation studies. The hardness test was undertaken employing the Rockwell method where the fracture surface was observed using a scanning electron microscope (SEM) in order to identify crack initiation and the type of fracture. The stress intensity factor was next analysed using the finite element method (FEM). The results of the chemical composition testing indicated that the material used was according to the AISI 8620 standard containing an element of Carbon (C) of about 0.142 %.The hardness value of the gear was 109 HRB. The observation of the fracture surface showed a brittle fracture surface, suggesting that an impact load had occurred. The simulation results using the FEM also showed that the maximum stress intensity factor and K_I value occurred at the centre of the tooth. The value of K_I was shown to be larger than the fracture toughness and (K_IC). Therefore, this result indicates that a crack will continue to propagate until final failure.

Abstract: This research focus on catalytic hydrotreating of Jatropha Bio-oil derived fast pyrolysis into biofuel was investigated to determine the effects of the supported type (Al₂O₃ TiO₂ and Al₂O₃-TiO₂ mix-oxide) and of the variables temperature (300-340 °C). The synthesized catalysts were prepared by sol-gel method for support and wet-impregnation with solution promoter on support, and characterization by BET NH₃-TPD XRD and NO-TPD for active site analysis of catalysts. The reaction was carried out in a Parr batch reactor under H₂ atmosphere about 50 bar for 2 h. The catalytic activity was evaluated for % fatty acid conversion (%FFA), %HDO, %selective to paraffin/olefin products. The results showed that the CMA gave the %FFA is highest, but low selective products, then the CMT gave the % HDO high than CMA, while the mixed-oxide were proving the %HDO, %FFA conversion and % selective is increasing because the TiO₂ incorporated with Al₂O₃ effect to increase the amount of rim site, it’s active site for HYD partway.

Abstract: The open pit mine is excavation soil from the Earth's surface, leading to presence of cut steep slopes with stability-concerned manners. Mae Moh open pit mine has the main component of claystone with ambiguous properties under stress condition changes from mine operations. Therefore, the strength of the claystone must be studied to be used for the slope stability analysis. Shear strength parameters for slope stability analysis were derived from the Triaxial Compression tests. Claystone is a type of sedimentary rock. Therefore, it is necessary to improve the equipment of the triaxial compression strength test to fit with intrinsic soft rock characteristics of the Mae Moh Claystone. Determination of parameters was based on Mohr Coulomb model, because it is the basis for slope stability analysis and can be resulted from the triaxial compression test. In addition, many computer-based programs for slope stability analysis also were relied onthe Mohr Coulomb model, including PLAXIS used in this study. Before the analysis, the model were validated by the function of “Simulation of Lab Test” in PLAXIS. Comparison on triaxial compression test results between the Mohr-Coulomb Model from PLAXIS and triaxial compression tests were made. This article reported the strength characteristics of Mae Moh claystone.

Abstract: At present, our world is facing environmental issues, which is an increasing amount of carbon dioxide (CO₂) generated by the Portland cement (OPC) production. To reduce that carbon dioxide emissions, some researchers have studied the alternative cementitious materials to replace the consumption of OPC, and geopolymer is one of the choices. Geopolymer cement (GP), a green technique for construction material, was applied for the road constructions by using Crushed rock (CR-the typical pavement material) as a starting material of geopolymer synthesis. The results showed that the optimum mixture to achieve both properties and economic aspect was 5M of NaOH concentration, 1.0 SS/SH ratio, 0.5 L/B ratio cured at room temperature. With that mixture, it passed the target compressive strength of Cement-treated base (CTB) for pavement (2.1-5.5 MPa) as well as achieving the CO₂ reduction of 45.23% when compared to ordinary Portland cement.

Abstract: High demand for using parts of natural materials, e.g., cores, fibers or leaves, as alternative additives are being increased. The main reasons are that natural materials can be served as renewable and eco-friendly choices such a sustainable development. Nevertheless, some limitations of applying those natural products, such as biodegradation, UV degradation, or weak bonding, are raised and need to be modified before further handling. One of the modification techniques for bio-based materials is chemical treatment by using alkaline solution (alkalization). Treatment process allows the plant's fiber to have fewer impurities as well as to increase the bonding on its contacting surface area. This research focuses on (i) effects of NaOH solution concentration on the pre-treatment properties of hemp fibers and (ii) self-treatment behavior of hemp fiber in geopolymer composites. The results show that the concentration of NaOH solution directly affected the pre-treatment process of hemp fiber as higher concentration from 1, 3, 5, 8, 10 to 12 Molar provided more vanishing level of fiber impurities, indicated by Contact Angle (CA) measurement and Fourier Transform Infrared (FT-IR) Spectroscopy analysis. With the concept of alkaline treatment, the self-treatment process was therefore applied for hemp fiber incorporated in alkaline-activated geopolymer matrix. The results illustrate the self-treatment behavior of hemp fiber in geopolymer composites, which could improve the final performances of the hardened products without conventional pre-treatment process.