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Start date: 2020Subject: search.filters.subject.Central composite design

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    Mineral filler characteristics and non-Newtonian viscosity of asphalt mastic at high temperature: A response surface methodology approach
    (2026-12-01)
    Chamwon, Suwaphit
    ;
    Hutabarat, Multazam
    ;
    Chaturabong, Preeda
    Asphalt mastic—composed of asphalt binder and mineral filler—strongly governs the high-temperature viscosity of asphalt concrete during mixing and compaction. This study investigates the effects of four mineral fillers (granite, limestone, shale, and pumice) on the viscosity and flow behavior of asphalt mastics at elevated temperatures (130–170 °C). Comprehensive filler characterization was performed, encompassing morphological analysis by scanning electron microscopy (SEM), physical property evaluation (particle density, specific surface area, and Rigden voids), hydrophilic coefficient determination, particle size distribution by laser diffraction, and mineralogical identification by X-ray diffraction (XRD). Response surface methodology (RSM) with a central composite design (CCD) was employed to model the combined effects of temperature (130–170 °C), filler content (5–30% by volume), and rotational speed (10–30 RPM) on apparent viscosity measured by a Brookfield rotational viscometer. The non-Newtonian index, derived from the power-law (Ostwald–de Waele) model, was used to classify flow behavior. Results demonstrate that temperature and filler content are the dominant parameters governing viscosity, while rotational speed controls the degree of non-Newtonian behavior in a filler-dependent manner. A critical transition from quasi-Newtonian to pronounced non-Newtonian flow was identified at 15–20% filler content by volume, coinciding with a sharp increase in the effective solid volume fraction that approaches the colloidal packing threshold (φ* ≈ 32–34%). Pumice exhibited the strongest shear-thickening (n up to 1.22) while granite showed consistent shear-thinning (n ≈ 0.88–0.94), with limestone and shale showing mixed behavior. Pumice and shale produced the strongest viscosity stiffening, consistent with greater binder immobilization due to their higher Rigden voids. AASHTO T316 workability analysis indicates that under base-binder conditions, the maximum filler content within practical mixing limits at 160 °C is approximately 30% for granite and limestone but only ∼22% for pumice. The validated quadratic RSM models (R² = 0.84–0.96) provide a practical framework for optimizing filler selection and processing temperatures in asphalt mixture design.
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    Enhancing biodiesel yield and purification with a recently developed centrifuge machine: A response surface methodology approach
    (2024-04-15)
    Limmun, Warunee
    ;
    Chungcharoen, Thatchapol
    ;
    Rattanamechaiskul, Chaiwat
    ;
    Phetpan, Kittisak
    ;
    Limmun, Wanida
    Biodiesel production processes, such as gravity settling, have limitations in terms of biodiesel yield, purification efficiency, operating time in the separation process, and more extensive equipment. Therefore, this study has focused on using a recently developed centrifuge machine for biodiesel separation to address these challenges due to its compact design, high efficiency, and simplicity. Additionally, this study aimed to optimize the separation efficiency of glycerol from biodiesel using a centrifuge machine, employing response surface methodology (RSM) with central composite design (CCD). The optimum conditions for separating glycerol from biodiesel via centrifuge machine are a rotation speed of 1800 rpm, a mixture flow rate of 192.25 ml/min, and a temperature of 55 °C, respectively. In optimum conditions, 94.52% separation efficiency was achieved. Biodiesel production can be improved, leading to higher yields and greater purity. The utilization of RSM proved valuable in determining the optimum conditions for separation. Furthermore, the machine successfully separated the biodiesel to meet ASTM D6751 and EN 14,214 standards. The results highlight the potential of the centrifuge machine for efficient and reliable biodiesel production, contributing to the advancement of the biodiesel industry.