Applied Mechanics and Materials Vol. 815

Abstract: Fly ash is a waste material from burning coal that can be used to reduce the amount of cement in making concrete and to improve the characteristics of concrete. Besides being able to improve the flowability of fresh concrete, fly ash can also serve to reduce cracking of concrete. But in certain cases, cement paste incorporating fly ash type C (high calcium fly ash) experiences cracks, right after being released from formwork. The purpose of this study were to investigate the causes of cracking of cement paste incorporating fly ash type C, the influence of fly ash variations, and the countermeasures. The evaluation conducted for this experiment were based on visual inspection and compressive strength test of cement paste at 28 days. Test specimens were made in the form of cement paste with fly ash content of 50%, by mass. Fly ash used was of type C taken from three different batches from one source; with fly ash type F from three different sources used for control specimens. Superplasticizer, silica fume, and calcium carbonate were used as additives to evaluate their effect in mitigating cracks. The results show that the use of fly ash type C may cause cracks on the surface of hardened paste. Fly ash content, especially CaO and MgO, are the key factors affecting the cracks tendency on the surface of cement paste, due to expansion. Superplasticizer and silica fume can be used to mitigate cracks of cement paste.

Abstract: Utilization and suitability of bottom ash in Portland cement have been increasing significantly in recent year. Bottom ash has substantial effects on mechanical properties with different composition of replacement in mixture of bottom ash and Portland cement. Bottom ash was used to determine the feasibility of the substitution as recycling product from industry depending on the percentage of the bottom ash. On the other hand, bottom ash offers a better solution for maintaining materials characteristic of Portland cement mortar and also provide beneficial mechanical performance. The result of using bottom ash in Portland cement mortar showed that it could make better the mechanical properties and hence disposed bottom ash wastes safely in technical, economic and environmental methods.

Abstract: This paper investigates the potential and suitability of flood mud to be used in geopolymer technique as construction materials. Flood mud was collected from Kelantan, Malaysia and crushed and sieved into powder form. Then, it was mixed with alkaline activator solution (mixture of NaOH and Na₂SiO₃ solutions) followed by curing process to produce flood mud geopolymers. In addition, the effect of varying solids/liquid (S/L) and Na₂SiO₃/NaOH ratios on the compressive strength of flood mud geopolymers were also investigated. The result showed that flood mud can be potentially used as precursor materials for geopolymer formation with favorable strength. Optimum compressive strength (24.6 MPa) of geopolymers based on flood mud was obtained at S/L = 1.25 and Na₂SiO₃/NaOH = 1.0.

Abstract: This paper studies the effect of curing temperature and curing duration to the flood mud based geopolymer on compressive strength properties. Flood mud was used as a raw material for geopolymer and geopolymer samples were synthesized by using sodium silicate and sodium hydroxide 14M solution. These samples were cured at different temperature (100°C, 150°C, 200°C and 250°) for different curing duration (6h, 12h and 24h) respectively. Compressive strength tests were carried out at after 28 days. The compressive strength and SEM analysis of geopolymer products were evaluated. Result showed that the maximum compressive strength was 24 MPa at temperature of 150°C for 24 hours. With increasing ageing day, densification of geopolymer gel was observed.

Abstract: This study reported thermal stability of hybrid sol-gel encapsulation materials doped with lanthanides complexes for generating white light. Red and green lanthanide phosphor, Eu (tta)₃phen and Tb (4DBBA)₃TPPO were incorporated into VTES:TEOS hybrid sol-gel and dispensed into 360 nm to 390 nm UV LED packages. Thermal properties of developed encapsulation material were analysed by TGA. A thermal aging test up to 96 hours was done to check the stability of developed encapsulation material towards UV LED junction temperature of 120°C and the luminescence properties changes was observed using photoluminescence measurement. To check the encapsulation material stability on forward voltage, the operation voltage has been increased from 3.0V to 4.0V. The photometric measurement were recorded using integrating sphere for the properties of Colour Rendering Index (CRI), colour temperature and Commission Internationale de L’Eclairge (CIE) colour coordinates. Based on the results, developed encapsulation material produced white colour with CIE colour coordinate of (0.32, 0.35), CRI up to 75 and colour temperature around 6000K.

Abstract: This paper is to study the dielectric properties, magnetic properties, and dielectric conductivity of Multi-walled carbon nanotubes (MWCNTs) and polyester (PE) composites. The composites with different amount of MWCNTs (5-15%) have been studied in the Ku-Band range (12.4-18 GHz). The rectangular waveguide (WR-62) was used to measure the dielectric properties and magnetic properties of the samples. The results show the dielectric properties and conductivity of MWCNTs/PE composites is increasing with the MWCNTs filler increases. The real part of dielectric properties values increase from 5.5 to 26.6 with increasing the MWCNTs loading from 5 % to 15 %. The increasing of MWCNTs filler in the MWCNTs/PE composites does not effects on magnetic properties, the real part and imaginary part of magnetic properties are approximate to 1 and 0. The highest conductivity of 15 % MWCNTs loading is reach to 11.02 (S/m) at 18 GHz. Keywords: composites, dielectric properties, magnetic properties, conductivity

Abstract: Metallic Fe₈₀Cr₂₀ alloy in thermal stability analysis is investigated. Approached method is combination technique (milled and UT) of ball milling (milled) combined with ultrasonic technique (UT) which is not yet fully explored. From Energy Dispersive x-ray Spectroscopy (EDS) analysis resulted that the composition of 80 wt% Fe and 20 wt% Cr in individual particle was achieved at milled and UB 4.5 h sample. Higher thermal stability of treated samples approximately 63% at 1100 °C temperature operation which showed by milled and UT at 4.5 h when compared to raw material. Combination technique shown high prospect to advance exploration in improving thermal stability which suitable for interconnect application.

Abstract: The importance of knowing dielectric value on a medium is to perceive the capability of conducting electromagnetic wave. Most of failure on electromagnetic instruments, were due to an inaccuracy of selecting material. Improper usage of materials may cause the attenuation of electromagnetic energy. So, it is important to measure the attenuation value. In this study, we compared the attenuation value on three media such as clay, silicon and wood. The problem mentioned above, could resolved by applying the electromagnetic propagation formula using skylab program. In this study we compared the effect constitutive parameters to the attenuation value and frequency in three media. The result shows, among three materials, at the same frequency we obtain that electromagnetic energy much easily attenuated on clay compared to other materials followed by silicon and wood. The reason is due to the conductivity value. In this study, we obtain that clay is the most sensitive on attenuation value on frequency followed by silicon and wood.

Abstract: Water based Remazol Brilliant Red, Orange and Violet dyes were used as the dye sensitizer in dye-sensitized solar cell. The performance of the solar cell was investigated between the dye concentrations, 0.25 mM and 2.5 mM and three different soaking times which at 3 hours, 12 hours and 24 hours. The adsorption peaks of the dyes were observed using ultraviolet-visible-near infrared (UV-Vis-NIR) Spectrometer and the performance of the dye-sensitized solar cell was measured using Spectrum Parameter Analyzer (SPA). The results show that the device efficiency was increased with dye concentration, but, the DSSC performance at different soaking times performed differently with the previous study. The highest conversion efficiency of 1.125 % was obtained for Remazol Brilliant Red at concentration of 2.5 mM at 3 hours soaking time.

Abstract: This work is a preliminary study to investigate the growth of carbon nanofibres (CNFs) on monolayer graphene. The growth of CNFs on graphene has been performed by chemical vapour deposition (CVD) using ferrocene as the catalyst precursor and acetone as the carbon source. Ferrocene in acetone is introduced to the system via spray coating onto the substrate. Graphene film used in this study is grown on nickel (Ni) thin film, which is confirmed to be monolayer. Aligned CNTs are unintentionally obtained, however only at the graphene/Ni thin film edges.