International Journal of Engineering Research in Africa Vol. 76

Abstract: Welding is the process of permanently joining materials and tungsten inert gas (TIG) welding is widely used due to its precision, controlled heat input, and cost-effectiveness. This study investigates the stress corrosion behavior of TIG-welded 304L stainless steel in a saline environment, analyzing factors contributing to material degradation. The research involved tensile testing and fractographic analysis to characterize fracture modes and determine the key influences on mechanical strength. Additionally, a microstructural analysis of the heat-affected zone (HAZ) was conducted to assess changes induced by welding. The results indicate that exposure to a chloride-rich environment led to a reduction in mechanical properties, primarily due to the formation of corrosion-related compounds and material thinning. Fractographic analysis revealed a transition in fracture modes, highlighting the influence of corrosion on failure mechanisms. Furthermore, microstructural examination showed significant alterations in the HAZ, which affected the overall integrity of the welded joints. These findings contribute to a better understanding of corrosion-induced degradation in welded 304L stainless steel and provide insights for optimizing welding parameters to improve durability.

Abstract: The increase in the temperature of photovoltaic (PV) cells is a critical factor that negatively affects the efficiency of converting solar radiation into electrical energy. This phenomenon not only reduces energy conversion efficiency but also causes damage to PV components, thereby preventing the achievement of the intended energy production goals. Moreover, the heating of PV modules has two significant impacts: first, a reduction in energy efficiency, and second, a decrease in the lifespan of the solar cells. Therefore, projects aimed at producing clean electrical energy using PV solar panels must consider the study of installation sites for PV solar plants and the impact of environmental conditions on panel performance. Given that an increase in PV cell temperature reduces their productivity, this study examines the impact of ambient temperature on the maximum temperature reached by a PV solar panel and analyzes the results. The results show that installing solar panels in harsh environments characterized by high temperatures, such as Ouarzazate in Morocco, can cause these panels to reach critical temperature thresholds of up to 115°C under high solar flux, which can lead to solar system failure and thus the failure of the entire project. In addition, the heating of photovoltaic modules has two major impacts: firstly, energy efficiency is reduced by around 0.44% for every 1°C increase, and overall efficiency is reduced from 16% to less than 10% under extreme conditions; secondly, solar cell life is shortened. Finally, this study highlights the importance of carrying out thorough climatic and environmental assessments before establishing solar photovoltaic power plants. It also highlights the importance of employing high-performance cooling systems or innovative technologies to reduce the impact of heat on photovoltaic panels. This approach is essential to ensure the longevity and efficiency of solar photovoltaic installations, and to achieve our ambitions for sustainable, green energy production.

Abstract: HVDC transmission systems are a prominent technology that enables efficient and economical long-distance power transmission and have potential advantages over HVAC transmission systems, such as leveraging the integration of asynchronous grid and RES to enhance reliable power supply. Still, its dynamic characteristics and ability to stabilize under small disturbances impose complexities to the overall system stability. With the objective of improving small signal stability in HVDC systems, this study investigated supplementary control strategies to dampen interarea power oscillations. Subsequently, this work proposed a strategy to implement an HVDC-based POD controller in the LCC-HVDC system to enhance small signal stability and ensure the reliable and secure operation of power systems. This study investigated the proposed strategy using the Kundur Two Area Four Machine system developed in PSCAD using three case studies with a three-phase to ground fault. The case studies are as follows: (i) base case of K-TAFM, (ii) integration of LCC-HVDC, and (iii) proposed HVDC-based POD controller with LCC-HVDC. The effect of the proposed HVDC-based POD controller gain has also been investigated in this paper. The comparative analysis between the LCC-HVDC POD-controlled system and the traditional LCC-HVDC configuration highlighted the superior performance of the POD controller across all key metrics, including damping ratios, settling times, and overall system resilience. Despite these advancements, the paper suggests further optimization, particularly through adaptive control strategies, to ensure robust performance under dynamic real-world conditions.

Abstract: In this study, distributed generators (DGs) based on renewable energy sources (RESs), besides capacitor banks are optimally allocated in power distribution networks with a proposed multi-objective optimization approach. The proposed approach is used to maximize the hosting capacity (HC) of RES DGs besides decreasing energy loss and voltage deviation in power networks. Uncertainties of load demand and RESs are considered. To facilitate the optimization processes, reduction criterion is utilized for reducing the numerous numbers of uncertain data. The proposed approach is applied to practical and standard power networks for many cases under the uncertain scenarios. Comparative study with other algorithms is performed and robustness of proposed approach is verified in long-term dynamic environment. Also, impacts of changing parameters values on performance are investigated. Additionally, Wilcoxon statistical tests are applied with the proposed approach. Also, comparative study is carried out between weighted sum and Pareto front techniques. Results reveal efficacy of the proposed approach with distribution power networks.

Abstract: Many factors influence the effectiveness of traditional binders used for soil stabilization, including anions present in the soil and carbonates. Natural pozzolana-lime stabilization is a relatively new technique that has shown promising results. However, no study has specifically evaluated its success in the presence of phosphate for high-carbonate soils. This paper investigates this question using marly soil from Medea, which was pre-contaminated with the common fertilizer monoammonium phosphate at 0, 2, 4, and 6% by dry weight, then stabilized with lime and/or natural pozzolana at 0, 8%, and 20%, respectively, by dry weight. To assess the effect of phosphate, mineralogical and macrostructural changes in these mixtures were analyzed through X-ray diffraction tests and scanning electron microscopy, respectively. Additionally, pH levels were monitored over 90 days, and changes in Atterberg limits between 1 and 30 days of curing were compared. Variations in immediate bearing indexes and compaction parameters were also examined. The study found that lime alone was ineffective in stabilizing the soil due to high carbonate content, with improvements in geotechnical properties only observed when natural pozzolana was added with lime. Phosphate was found to impact the lime-natural pozzolana stabilization technique significantly.

Abstract: Phosphogypsum storage poses a major environmental challenge for countries engaged in chemical fertilizer production due to the polluting nature of this industrial byproduct. To promote more sustainable waste management, mining companies are exploring alternative uses, including the construction of sludge retention dikes for liquid effluent containment. In this context, the Gafsa Phosphate Company initiated a project to build sludge retention dikes using quarry waste to store phosphogypsum, with potential applications in civil engineering. This study presents a numerical investigation of the mechanical behavior of sludge retention dikes constructed from quarry waste near Metlaoui City in southwestern Tunisia. Two complementary approaches were employed: the finite element method (FEM), using a plane strain model with the Mohr–Coulomb constitutive law, and the limit equilibrium method (LEM) to cross-validate stability results. Geotechnical parameters for both the foundation soil and dike materials were derived from in-situ and laboratory investigations. The analysis focused on optimizing slope geometry to ensure an adequate factor of safety by assessing the influence of slope angle and sludge height on dike stability before and after basin filling. For a slope inclination of 2V:1H, the factor of safety exceeded 1.4 using FEM and reached approximately 1.5 with LEM following sludge deposition. After deposition, the factor of safety increased on the upstream side to 5.55 and decreased on the downstream side to values ranging from 1.55 to 1.25, depending on the sludge height. Despite this reduction, all configurations maintained a factor of safety above 1.2, indicating a globally stable structure. Furthermore, steeper slope configurations were associated with lower factors of safety, highlighting the critical role of slope design in ensuring the overall stability of sludge retention dikes.

Abstract: The reuse of reclaimed asphalt pavement (RAP), sourced from the milling of existing pavements, offers an eco-friendly alternative to natural aggregates. It offers significant environmental benefits by reducing landfill waste and limiting the exploitation of natural resources. This study investigates the potential incorporation of fine RAP (FRAP) in the production of sand concrete, a particular type of concrete composed solely of fine aggregates. Firstly, five sand concrete mixtures were designed by partially or fully replacing natural sand with FRAP and were then assessed in terms of their mechanical characteristics and durability-related indicators. The results revealed that FRAP can be successfully used to produce sustainable sand concrete at replacement levels up to 50%, meeting all the mechanical performance requirements for pavement applications. The incorporation of FRAP also resulted in increased water absorption by immersion and higher sorptivity values. Yet, these values remained within the permissible limits for mixtures with 50% or less FRAP. Furthermore, given the critical role of elastic modulus in rigid pavement design, three predictive models were evaluated to estimate the elastic modulus of FRAP mixtures. The findings indicated that, when incorporating a correction factor reflecting aggregate quality, the ACI 318 model provided the highest accuracy, achieving a root mean square error of 1.5 GPa. The study confirmed the feasibility of reusing RAP in sand concrete, offering practical guidance for engineers to adopt this technique in pavement applications and encouraging greener construction practices.

Abstract: The emission of greenhouse gases during its production, and the poor performance of cementbased concrete in marine environments has raised the need for alternative eco-friendly materials. This study investigated the strength and durability of Geopolymer concrete cured in marine water. The Slag/Metakaolin-based geopolymer concrete was used in this study. Two curing regimes were adopted; a sample was cured in marine water while the control was air-cured and designated as GPCW and GPCD respectively. Geopolymer beams, cubes, and cylinders were used for flexural, compressive, and tensile tests, respectively, at 7, 28, 90, 180, 270, and 365 days. Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS) were used to determine the microstructural and elemental compositions. Results showed an increase in compressive, flexural and tensile strengths between 7 to 180 days, with a gradual decrease at 365th days for the GPCD samples. The GPCW showed a 43% reduction in strength between the 7th and 28th days, with a further decrease of 11% from 28 to 365 days. The average strength of both samples was above C40 grade concrete. SEM revealed differences in GPCD and GPCW with the latter displaying less dense structures with larger voids, consistent with the reduction in compressive strength over time. The EDS analysis showed that there was <1% ingress of Sulphate into GPCW on average, this revealed its resistance to the deterioration-causing agent in cement-based concrete. This study concluded that GPC can be used for coastal marine concrete structures.

Abstract: This study investigates the relationship between compressive strength and mid-span deflection of reinforced concrete beams, as determined through experimental tests and numerical modelling. Six commonly used concrete classes in Morocco (C10, C15, C20, C25, C30, C35) were prepared and tested to evaluate their mechanical performance. The obtained compressive strength values were incorporated into numerical models created using Robot Structural Analysis software, enabling the simulation of beam behaviour under uniform distributed load. Experimental results confirm that the compressive strength values comply with Moroccan standard NM 10.1.051, and they are strongly influenced by the paste volume and the water–cement (w/c) ratio. Moreover, the presence of superplasticizer helps to maintain workability by prolonging the slump. The findings indicate that mid-span deflection increases with compressive strength, highlighting the close connection between material properties and structural response. This approach demonstrates the value of combining laboratory experimentation with numerical modelling to bridge the gap between academic practice and real-world applications in civil engineering.