International Journal of Engineering Research in Africa Vol. 77

Abstract: The kinetics and mechanism of transesterification of Shea butter to produce fatty acid methyl ester (FAME) were investigated using a catalyst developed from clay impregnated with barium chloride (CD-BaCl₂). The catalyst was prepared by mixing 10% BaCl₂ chloride with clay, drying it, and calcining it at 600°C for four hours. The synthesized catalysts were characterized using X-ray Diffraction (XRD), Scanning Electron Micrograph (SEM), Brunauer-Emmett-Teller (BET), X-ray Fluorescence (XRF) and Fourier Transform Infrared Spectroscopy (FT-IR) to determine their suitability. The effects of methanol/mol ratio, catalyst concentration, temperature, agitation speed and time on FAME production were evaluated using the synthesized catalyst. Two elementary reaction mechanisms, Eley-Rideal (ER) and Langmuir-Hinshelwood-Hougen-Watson (LHHW) were used to analyze the kinetics. CD-BaCl₂ effectively converted Shea butter into FAME, and variations in the process parameters had a significant impact. A 4wt% catalyst dosage, a 10:1 methanol/oil molar ratio, a 2-hour reaction time, a speed of 300rpm, and a temperature of 60°C resulted in approximately 70% FAME. The kinetic results showed that LHHW provided the best representation of the experimental data with the CD-BaCl₂ catalyst. The rate-determining step (RDS) was the surface reaction linking the adsorbed triglyceride and adsorbed alcohol. The rate increased with temperature, indicating an endothermic reaction. The activation energy and frequency factor for the reaction were 2.49 kJ/mol and 8.61 h^-1, respectively, occurring at a temperature below the boiling point of methanol. The model's capability was evaluated by validating the experimental data, showing a good relationship. Keywords: FAME, shea butter, LHHW, ER, clay

Abstract: This paper reports the complete setup of water atomisation machine designed to manufacture aluminium powder out of discarded aluminium metal in Nigeria. It is a study that evaluates the country’s dependence on imported aluminum powder and the economic effect its has on the country. The specially designed atomizers with high-pressure water supply, atomising nozzles, and tanks turn discarded aluminum scrap into powder in 45 seconds. The studies consist of iterative design optimization and parameter tuning, 82% conversion and aluminium powder manufactured with desired properties.Finite element analysis (FEA) checks the structure for integrity at high pressures; and computational fluid dynamics (CFD) analysis explains thermal dynamics. The results are positive for the domestic aluminum market as it offers a long-term and affordable alternative for aluminum powder production.

Abstract: This research investigates the progressive substitution of natural aggregates, conventionally used in road construction, with alternative materials derived from industrial co-products. Specifically, the study focuses on developing an innovative material that combines shale aggregates and blast furnace slag for road construction applications. The experimental procedure involved preparing various mixtures with slag content ranging from 10% to 50%, followed by comprehensive laboratory characterization through standardized mechanical and road performance tests. The results demonstrate that these composite materials exhibit highly promising characteristics. Mixtures containing 30–50% slag meet all current standard requirements, showing particularly excellent performance in bearing capacity (with CBR values reaching 62.15 for the 50% slag mixtures), while maintaining outstanding water stability (with variations of less than 4% after immersion).These mechanical properties, combined with consistent dry density values above 2.1 g/cm³ and a maximum internal friction angle of 43.53°, make these materials especially suitable for pavement layers. Beyond their technical performance, the shale–slag composites offer a sustainable solution with dual benefits: they significantly reduce pressure on depleting alluvial deposits while effectively valorizing abundant industrial by-products.Based in these findings, it is strongly recommended that such materials be integrated into conventional pavement construction, particularly for low to medium traffic. This circular economy approach therefore represents both a high-performance and environmentally responsible alternative to traditional materials.

Abstract: Back-to-Back Mechanically Stabilized Earth (BBMSE) walls in near slopes present complex stability challenges not fully addressed in current design standards. While most previous studies focus on isolated retaining walls, this study pioneers the investigation of coupled mechanical interactions between twin BBMSE walls under slope inclination (β = 35°, 40° and 45°). Employing advanced finite element modeling (FEM) (PLAXIS 2D), we systematically analyze three governing parameters: (1) slope angle (β); (2) wall-to-slope crest distance (Lₓ = 0.5, 1 and 1.5 m), and (3) geosynthetic reinforcement stiffness (J = 1100, 5000 and 10000 kN/m). The results quantify how these parameters influence failure mechanisms, peak tensile forces, wall displacements, and lateral earth pressures. The outcomes demonstrate that geometric configuration (β ; Lx) and reinforcement stiffness (J) are critical for BBMSE walls system stability. The horizontal displacement of the walls was observed in unequal, as the value on the right wall was greater than the left wall (the difference reaches 17%) . and the maximum tension in soil reinforcement were found to be unequal between the right and left sides due to the slope. The results highlight the critical role of geometric configuration and reinforcement properties in enhancing the performance of back-to-back walls on sloped ground and these findings challenge conventional design approaches and provide actionable recommendations for optimizing BBMSE walls in sloped environments.

Abstract: Accurate prediction of tunnel water inflow (WI) is critical for preventing construction hazards and supporting engineering decision-making. This study proposes an enhanced stacking machine learning framework to achieve reliable WI prediction. SMOGN technology was used to address the issue of imbalanced data distribution. On this basis, the Bayesian optimization tool Optuna was utilized for automated hyperparameter tuning of various base learners, including elastic net (Enet), multilayer perceptron (MLP), support vector regression (SVR), and extreme gradient boosting (XGBoost). Base learner outputs were combined with original features to form augmented inputs, with ridge regression as the meta-learner. Gaussian process regression (GPR) modeled residuals for uncertainty quantification, while the Sobol method assessed feature importance. Results show that feature augmentation and residual modeling improve prediction performance. The proposed stacking model outperforms individual base models and achieves state-of-the-art results. From an engineering perspective, the framework can be used to forecast potential high-inflow zones, guide advance grouting or drainage measures.

Abstract: This study examines the influence of low proportions (<2.5%by mass) of 40/63 mm gravel on the shear strength of hardfill used in the Mallegue-Amont Dam (Tunisia). To address the coarse nature of the material, a custom medium-scale direct shear apparatus was developed, despite its non-standard dimensions. Nine mixtures with varying sand-to-gravel ratios were prepared to evaluate the effect of fine content. Experimental testing was supported by statistical analysis and validated through numerical simulations using FLAC3D. Results indicate that the 40/63 mm fraction has a negligible effect on shear strength parameters. Instead, the mechanical response is predominantly controlled by cementation and particles smaller than 40 mm. Numerical modeling confirmed the reliability of the experimental findings and reinforced the validity of the adapted testing approach. The study demonstrates that representative shear strength parameters can be obtained using non-standard equipment, provided mixture preparation and mold dimensions are carefully controlled. These insights contribute to cost-effective hardfill design and improved durability of dam and infrastructure projects.

Abstract: This paper presents the results of a study that aimed to analyze the flexural behavior of self-compacting rubberized steel-reinforced concrete. A four-point bending test was performed on three reinforced beams made with conventional concrete and three similar beams made using the same concrete mixture with a 10% volumetric substitution of natural aggregates with rubber particles. The results showed a statistically significant decrease (about 24%) in the cracking load for the rubberized concrete beams, which is attributed to the reduced indirect tensile strength and modulus of the rubberized concrete. However, no statistically significant difference was observed between the control and rubberized concrete beams in terms of ultimate load and maximum deflection Additionally, the estimated adhesion strength, based on the average measured crack spacing, was also statistically similar between the tested beams. Existing equations derived from reinforced concrete beam theory were deemed suitable for rubberized concrete, since the estimation trends for these equations were similar for both types of concrete. Therefore, the main conclusion of this study is that the presence of rubber particles, at a 10% volumetric substitution, did not affect the flexural behavior particularly the quality of adhesion between the reinforcing bars and the surrounding concrete of steel-reinforced beams.

Abstract: This study evaluates the impact of replacing natural sand (NS) with quarry waste sand (QWS) or recycled concrete sand (RCS) at varying substitution rates (0%, 25%, 50%, 75%, and 100%). The analyzed properties include Abrams cone slump, superplasticizer demand (SP), rheological and tribological parameters, mechanical strength, capillary water absorption, and shrinkage. The results show that QWS-based concrete exhibits better workability and requires less superplasticizer, whereas RCS-based concrete necessitates a higher admixture dosage. Both QWS sand and RCS sand significantly enhance the rheological and tribological properties of concrete Moreover, QWS sand provides higher mechanical strength than NS sand, with a strength gain of up to 16% at full replacement (100% QWS sand) at 90 days. Conversely, RCS sand reduces compressive strength by 28.6% at 28 days. and negatively affects porosity and capillary water absorption. However, these negative effects are mitigated when the RCS sand replacement is limited to 25%. QWS sand-based concrete exhibits slower shrinkage and reduced deformability compared to NS sand-based concrete. Predictive strength models were established based on experimental parameters, displaying a high correlation coefficient and a low root mean square error. Replacing NS sand with QWS sand or RCS sand reduced production costs, lowered carbon emissions, minimized waste, and preserved natural resources, offering a sustainable approach for concrete applications.

Abstract: Continuous water quality monitoring remains a potential concern because of its connection to human wellbeing and aquatic ecosystem. This study examines seasonal variation of TSS concentration in Lagos Lagoon surface water. The Lagoon is located in South-west coastal region in Nigeria known to be extremely contaminated because of its vulnerable location, increasing human activities and infestation from nearby creeks. The investigation utilized Landsat 8-9 multispectral spatial bands (OLI & TIR) while band combination indices, such as WRI (Water Ratio Index) and NSMI, (Normalized Sediment Material Index) that used blue, red, green, NIR and SWIR Band was utilized respectively. Automated Water Extraction Index (AWEI) was employed for further confirmation of sediment concentration. Linear and nonlinear regression testing was used to analyse the correlation between the remotely sensed data and the in-suit data. Result revealed modest undesirable correlation between the employed indices and the real time in suit data reflecting non alignment relationship. Nonlinear equation testing reported highest = (0.42) which is slightly stronger than the linear case with highest (0.27). The dry season equally reports considerably more total suspended solids and turbid particles than the wet season. The final outcome effectively proved the capability of Landsat improved sensor bands in retrieving TSS in Lagoon surface water.

Abstract: This study aims to optimize the protection of photovoltaic (PV) systems against electrical disturbances, particularly voltage dips. The objective is to develop new methods for analyzing and managing these disturbances, which affects the power quality in electrical networks and causes the automatic disconnection of PV systems, leading to production losses and plant malfunctions. In addition, voltage dips represent a major challenge for industrial sectors, where they can cause production interruptions and process malfunctions, leading to economic losses and product quality degradation. This research proposes a method for real-time detection of voltage dips, by integrating the recloser settings within the monitoring system. This approach makes it possible to distinguish temporary outages, related to reclosing, from prolonged outages, thus avoiding unnecessary disconnections of PV systems. The method's performance has been validated by simulations carried out in the MATLAB/SIMULINK environment.