Browsing by Author "Lesafi, Fina"

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High-performance eco-concrete beams with calcined montmorillonite, metakaolin pyrolyzed coffee grounds, and hybrid fibers for enhanced bending strength and microstructural refinement
(PLOS One, 2026-03-05) Hepautwa, Amani; Hilonga, Askwar; Mrosso, Register; Alfredy, Tusekile; Mwalusambo, Gabriel; Lesafi, Fina; Chande, Yusufu
This study investigates the flexural performance and microstructural evolution of reinforced concrete beams incorporating calcined montmorillonite (CMMT), metakaolin (MK), pyrolyzed coffee grounds (PCG), and hybrid fibers (steel or banana) as sustainable partial replacements for natural sand and cementitious binders. The replacement levels—12.5% SCM (CMMT or MK) and 15% PCG—were selected based on preliminary optimization trials and evidence from prior studies that identify these ranges as the threshold at which pozzolanic reactivity, workability, and particle packing achieve maximum benefit without compromising matrix integrity. Thirteen mix groups and a control beam were cast and tested under four-point bending, with three replicates per group. Statistical analysis using one-way ANOVA (α = 0.05) confirmed significant differences in peak load, stiffness, ductility, and energy absorption across mixes (p < 0.05). Beams containing CMMT and 1.5% steel fibers achieved the highest flexural capacity, exhibiting a 92–105% increase in ultimate load relative to the control, while mixes with 1.0% banana fibers demonstrated the greatest ductility and post-cracking deformation capacity. Improvements in stiffness (up to 68%) and energy absorption (up to 120%) were closely linked to microstructural refinement observed through XRD and SEM. Quantitative indicators—including a 22–34% reduction in portlandite peak intensity, an increase in amorphous C–S–H content, and visibly compacted interfacial transition zones—corroborated the enhanced matrix densification induced by CMMT and PCG.The combined use of PCG, CMMT, and natural/steel fibers significantly reduced reliance on natural sand and cement while improving structural performance, demonstrating a viable pathway for developing high-performance eco-concretes for structural applications. Although direct durability tests were not conducted, the observed microstructural densification suggests potential improvements in long-term resistance to moisture and chloride ingress, warranting further research.
Mechanical, durability, and thermal performance of concrete incorporating coffee biochar and raw and calcined montmorillonite
(Frontiers, 2026-04-21) Hepautwa, Amani; Hilonga, Askwar; Mrosso, Register; Alfredy, Tusekile; Lesafi, Fina; Jande, Yusufu
Introduction: Montmorillonite is a natural aluminosilicate clay with potential as a supplementary cementitious material, although its reactivity in the raw state is limited. This study investigates the effect of raw and calcined montmorillonite on the performance of concrete incorporating 15% pyrolyzed coffee grounds (PCG) at 350 °C.Methods: Montmorillonite calcined at 400, 600, and 800 °C replaced cement at levels of 5%–20%. Mechanical and durability properties were evaluated under acidic, saline, and thermal exposure conditions. Microstructural characterization was conducted using FTIR, XRD, and SEM, and statistical validation was performed using two-way ANOVA.Results: Calcination enhanced montmorillonite reactivity through amorphization and pozzolanic reactions, resulting in improved pore refinement and matrix densification. Specimens with calcined montmorillonite at 600 °C–800 °C showed superior strength and durability performance.Discussion: The combined use of calcined montmorillonite and 15% PCG biochar at 350 °C provides a sustainable approach for improving concrete performance.
Sustainable Plywood Production: Enhancing Cardanol Formaldehyde Bio-Resin With Nanocellulose Fibers From Sugarcane Bagasse
(Wiley Online Library, 2025-10-15) Kimani, Cryspian; Lesafi, Fina; Maagi, Mtaki; Kichonge, Baraka; Kivevele, Thomas
With the rising demand for sustainable materials, the plywood industry is turning to bio-resins as an eco-friendlier alternative to traditional fossil-based resins. However, the poor physio-mechanochemical properties of the bio-resins limit their applications. This study seeks to enhance these properties by integrating nanocellulose derived from sugarcane bagasse into cardanol formaldehyde resin. The resin was synthesized via polycondensation under acidic conditions, and nanocellulose was prepared using acidic hydrolysis. Nanocellulose was added at concentrations of 3%, 5%, 7%, and 10% to create reinforced nanocomposites, which were used to fabricate plywood panels and subjected to mechanical and physical properties tests. The modified resins were subjected to chemical and morphological tests. Results revealed significant improvements, with 7% nanocellulose resin achieving a peak breaking strength of 39.52 ± 2.1 MPa, compared to 13.16 ± 1.2 MPa for unmodified resin. While 10% nanocellulose reduced strength due to over-interaction of the nanocellulose, all concentrations above 3% exceeded the 20 MPa industry standard. Thermal stability of the nanocomposite was enhanced, with decomposition and glass transition temperatures increasing to 473°C and 453°C, respectively. These findings underscore the potential of nanocellulose-reinforced bio-resins as high-performance, sustainable materials for plywood manufacturing.
Tin molybdenum mixed metal oxides catalyst for oxidative desulfurization of model diesel
(NM-AIST, 2023-08) Lesafi, Fina
This study reports on synthesis, characterization, and catalytic activity of mesoporous mixed metal oxides of tin (Sn) and molybdenum (Mo) for sulfur removal from model diesel. Variable synthesis conditions, namely calcination temperature and Sn/Mo mole ratios, have been on focus. Several techniques were used to characterize the catalysts, including powder X-ray diffraction (XRD) for the crystal structure, orientation, and particle size; scanning electron microscopy (SEM)-EDX for examining the morphological properties of the materials, N2 adsorption-desorption isotherms for textural properties, thermal gravimetric analysis (TGA) for thermal stability, the Fourier transform infrared spectroscopy (FT-IR) for functionality. Characterization results show that the adsorption-desorption isotherms are of type IV, indicative of mesoporous materials. The surface area of the synthesized materials decreased as calcination temperature increased due to the Ostwald ripening process and increased with the mole ratio Sn/Mo increase. The X-ray diffraction structural analyses revealed that the synthesized catalyst had a tetragonal structure. The presence of Mo=O and Sn‒O‒Mo bonds, which are responsible for the catalytic reaction, is confirmed by FT-IR and Raman analyses. The activity of the catalysts prepared at various calcination temperatures and mole ratios was analyzed for oxidative desulfurization of model diesel, dibenzothiophene (DBT). The optimal synthesis conditions were the calcination temperature of 450 °C and the mole ratio of Sn/Mo of (2:1). Other multiple parameters affecting the reduction of sulfur compounds were also investigated, including reaction temperature, catalyst loading, oxidant/sulfur ratio, and reaction time. The (DBT) removal efficiency was 99.8 % at 60 °C, 100 mg, 5, and 30 min, correspondingly. This high catalytic activity was due to the surface defects increase,resulting in a high surface area with high pore distribution around the mesopore region. Experiments examining the reaction kinetics have indicated that the reaction follows a pseudo first-order behaviour. The activation energy for the reaction has been determined to be 36 ± 4 kJ mol-1. The rate of the heterogeneous reaction is governed by the Langmuir-Hinshelwood mechanism. Furthermore, the maximum rate constant value of SnO2-MoO3 catalyst with Sn/Mo (2:1) molar ratio is 0.057 min−1, which is higher than for pure SnO2 (0.017 min‒1) and MoO3 (0.007 min−1), confirming a synergy between SnO2 and MoO3, promoting oxidative desulfurization efficiency. The catalyst's high activity and reusability indicate enormous promise for industrial catalytic desulfurization.