AAU Institutional Repository (AAU-ETD)
Addis Ababa University Institutional repository is an open access repository that collects,preserves, and disseminates scholarly outputs of the university. AAU-ETD archives' collection of master's theses, doctoral dissertations and preprints showcase the wide range of academic research undertaken by AAU students over the course of the University's long history.
How to Submit Your Work
The repository contains scholarly work, both unpublished and published, by current or former AAU faculty, staff, and students, including Works by AAU students as part of their masters, doctoral, or post-doctoral research
- All AAU faculty, staff, and students are invited to submit their work to the repository. Please contact the library at your college.
You may contact digirep@aau.edu.et.with any questions about the repository
Colleges,Institutes in AAU-ETD
Select a college,institute to browse its collections.
Recent Submissions
Investigating EFL Students’ and Teachers’ Attitude and Practice of Code-switching: Mekelle University in Focus
(Addis Ababa University, 2025-08-01) Gebrewahid Tsige; Hailom Banteyerga(PhD)
Whether or not to code-switch in the teaching and learning process of EFL classes is one of the controversial issues. This dissertation is, thus, conducted to investigate EFL students’ and teachers’ attitude towards code-switching and their practice. To achieve this objective, data were collected from 109 students and 50 teachers of English major at Mekelle University. The participants were chosen using available sampling. In this study, the descriptive research design was employed. Data for this study were gathered using classroom observation audio records, questionnaires, and interviews. The gathered data were analyzed both quantitatively and qualitatively. The quantitative data were analyzed using frequency counts, percentages, Kruskal Wallis H test, Mann Whitney U test, and ordinal logistic regression. The results indicate that the teachers’ attitude towards code-switching was more positive than their students,and the difference was significant. It is also found that the teachers code-switched more frequently than the students though the difference was not significant.The results disclose that the students’ code-switching practice increased as their class year increased. Regarding the dominant pattern of code-switching, first year students employed intra-sentential while both second year and third year students practiced inter-sentential pattern of code-switching. The teachers of all class years, too, frequented inter-sentential pattern of code-switching more dominantly. Besides, the obtained results show that students of all class years and their teachers used code-switching for curriculum access purposes dominantly. The results also disclose that there existed a statistically significant relationship between students’ demographic factors such as class year, mother tongue, type of school, parents’ educational status, Amharic language speaking skill, and attitude towards code-switching and their code-switching practice. Furthermore, a statistically significant relationship was found between teachers’ code-switching and their demographic factors like educational status, teaching experience, multilingualism, training on code-switching, and attitude towards code-switching. Based on the findings, it is concluded that the students’ and teachers’ code-switching usage was excessive.An excessive usage is abhorrent in multilingual classes where there are students who know little or no Amharic. Therefore, though a cautious and judicious use of code-switching has a lot of advantages, an over use of it diminishes students’ practice and exposure to the foreign language.This leads both students and teachers to be less competent in English language. In light of the findings of the study and the conclusions reached, recommendations to EFL students, EFL teachers, language policy planners, universities, the Ministry of Education, and researchers are made
Design, Manufacturing, and Performance Evaluation of Building-Integrated Asymmetric Compound Parabolic Concentrator Solar Evacuated Tube Collector with Concentric Tube Heat Exchanger
(Addis Ababa University, 2023-10) Biniam Tufa; Solomon Tesfamariam (PhD)
The amount of thermal energy consumed in buildings has increased due to the rapid development of urbanization. In most cases, high-rise buildings have a small ratio of available roof area to the required solar collector area to generate thermal energy. A wall-mounted Asymmetric Compound Parabolic Concentrator (A-CPC) solar evacuated glass tube collector with a concentric tube heat exchanger is designed to boost the solar energy collection for building thermal energy supply. The geometric profile of A-CPC was computed from the standard CPC geometry using solar altitude angles. TracePro and ray-tracing program, were used to predict the collector's optical efficiency. The collector's performance was evaluated using an experimental method in real-world conditions. The optical simulation result shows that, within the range of the solar altitude angle, the highest optical efficiency was around 73% and the average optical efficiency was around 58%. From the experimental result, the average instantaneous thermal efficiency for experiment-1, experiment-2, and experiment-3 was 51.2%, 52.86%, and 53.03%, respectively. Taking systematic and random error into account, the maximum uncertainty of instantaneous thermal efficiency was found to be 6.0%, 5.95%, and 5.94% for experiments 1, 2, and 3, respectively. The findings of this study shows that the A-CPC based collector performance is superior (by 1.63%) and has a high efficiency in comparison to other research studies being conducted in the field. Furthermore, the outcomes shows that, contrary to popular perception, solar collector integration on building walls at low latitude countries is viable and should be taken into consideration.
Partial Replacement of Cement with Municipal Solid Waste Incinerator Fly Ash in Concrete Production
(Addis Ababa University, 2025-02) Merem Sualih; Girma Zerayohannes (PhD); Esayas Gebreyohannes (PhD) Co-Advisor
Fly ash resulting from municipal solid wastes incinerator (MSWI) can be potentially reused as cement replacement in concrete. However, several researchers suggest that fly ash requires pre-treatment due to its high chlorine content to be used as partial substitute for cement in concrete. Currently large amount of fly ash is generated in thermal power plant as waste material with an improper impact on environment and humans in Ethiopia. Fly ash waste generated by Reppie thermal power plant is as such a big environmental concern.
This research examines the potential of using treated and untreated MSWI fly ash as partial replacement of cement in concrete production for saving waste disposal cost, conserving natural resource and for mitigating the environmental impact of cement production. This study aim to investigate early and late age mechanical and durability properties of untreated and treated fly ash concrete. In this research, the fly ash was treated by washing with water only to reduce the chlorine and sulfur.
Concrete mixture containing 0%, 10%, 15%, and 20% dosage of untreated and treated fly ash by volume were proportioned. The compressive and flexural based tensile strength result at three, seven, twenty-eight and fifty-six days and also the water permeability data for twenty-eight days are determined. The experimental outcome indicates that the compressive strength of treated fly ash is lower compared to untreated fly ash, but still fall with in an acceptable range when compared to the control mix. The compressive strength of washed fly ash concrete with 10% and 15% replacement ratio exceed the control group’s 28th-day strength by 0.15% and 3.78% respectively. However, the flexural strength decreases as the level of both washed and unwashed fly ash increase. Still, the washed fly ash at 10% and 15% replacement level exhibits acceptable result when compared to the control group. Moreover, the 10% and 15% washed fly ash replaced concrete sample possess a better water tightness performance than the controlled sample. Based on the result, the treated FA can replace cement up to 15%.
High-Temperature Performance of Concrete Utilizing Waste Ceramic Coarse Aggregate as Partial Replacement
(Addis Ababa University, 2025-02) Sarem Jezbu; Esayas Gebryouhannes (PhD)
The increasing demand for sustainable construction materials, along with the growing need for improved fire resistance in structural elements, has accelerated research into alternative aggregate sources for concrete production. In this context, this study investigates the high-temperature performance of concrete in which waste ceramic coarse aggregate, sourced primarily from discarded tiles and sanitary ware, is used as a partial replacement for natural coarse aggregates. The core aim is to address two pressing challenges in modern construction: enhancing concrete’s resistance to elevated temperatures and promoting the sustainable use of construction and industrial waste.
A series of concrete mixtures incorporating waste ceramic aggregate at replacement levels of 10%, 20%, 30%, 40%, and 50% by volume were prepared and subjected to both ambient conditions and elevated temperatures up to 600°C. After heating, specimens were cooled either gradually in a furnace or by immersion in a limited volume of water to simulate post-fire scenarios. Comprehensive tests were carried out to assess residual compressive strength, mass loss, and workability. The results demonstrated that concrete with 40% ceramic aggregate achieved the best overall performance, retaining more than 70% of its original compressive strength after thermal exposure. Water-quenched specimens consistently outperformed those cooled in the furnace due to shorter exposure to damaging high temperatures and the moderated thermal shock effects provided by steam and rising water temperatures.The superior performance of ceramic-modified concrete is attributed to several synergistic factors. The angular and irregular shapes of the ceramic particles contribute to improve internal packing, which reduces porosity and enhances strength. Moreover, the pozzolanic reactivity of ceramic materials due to their silica and alumina content supports secondary hydration reactions, thereby enhancing matrix cohesion and long-term durability. A stronger interfacial transition zone (ITZ) is formed, further improving the mechanical integrity of the concrete. Additionally, ceramic aggregates exhibit low thermal conductivity and high heat resistance, properties that significantly enhance the thermal stability of concrete under high-temperature exposure. Workability is also improved due to the smooth surface texture and lower water absorption rate of the ceramic aggregates, simplifying the mixing and placing process.
In Ethiopia, where construction activity is rapidly expanding and ceramic waste is increasingly abundant but underutilized, the application of ceramic aggregates offers a dual advantage: reducing environmental waste while supporting infrastructure development. The findings of this study suggest that up to 40% replacement of natural coarse aggregate with waste ceramic aggregate provides an optimal balance between mechanical strength, thermal resistance, and sustainability. This position’s ceramic-modified concrete as a viable solution for fire-resistant construction in hot or fire-prone environments.
In conclusion, this research demonstrates that waste ceramic materials can be effectively repurposed into durable and thermally resilient concrete, offering an eco-friendly and cost-effective alternative to conventional aggregates. The use of waste ceramic in concrete not only enhances mechanical and thermal properties but also aligns with circular economy principles by minimizing industrial waste and promoting resource efficiency. These findings contribute meaningful insights into sustainable construction practices, particularly in regions where exposure to high temperatures is expected, and encourage the development of policies and recycling infrastructure to support broader implementation.
Characterization and Anionic Reverse Flotation of Boreda Kakisha Iron Ore, Melo Koza, Gofa Zone, South Ethiopia Region
(Addis Ababa University, 2025-06) Wondishaw Wosine; Kebede Gamo (PhD)
Iron ore, a mineral or rock from which metallic iron is extracted, mainly consists of iron in the form of oxides, hydroxides, carbonates, and sulfides. The presence of impurities like silica, alumina, phosphorus, sulfur, and trace elements can affect the ore's quality and suitability for iron and steel production, often requiring processing to reduce impurities. Anionic reverse flotation was used in this work to examine the impurity removal procedure for low-grade BK iron ore. BK iron ore sample is the low-grade and contains Fe2O3 (26.26 – 31.20 wt%, average 29.73 wt %) as iron-bearing mineral and SiO2 (43.16 – 51.78 wt %, average 45.78 wt %) and Al2O3 (11.46 – 13.60 wt %, average 12.42 wt %) as major associated impurities based on AAS analyses. The XRD mineralogical analysis showed that the iron ore sample primarily consisted of hematite and goethite as the main valuable minerals, with quartz being the dominant gangue mineral. The effect of varying particle size range was studied in the flotation test. BK iron ore was upgraded through anionic reverse flotation using the following conditions: 2 ml of 2% corn starch solution, 2 ml of oleic acid, 2 ml of 1% calcium chloride solution, and 2 ml of pine oil, pH of 11 and particle size of -250+150 microns, which is optimal particle size range because of highest concentrate grade due to mineral liberation and less affected by slimes. Under these conditions, a concentrate with 23.92% Fe grade and 97.21% iron recovery was achieved. The average iron (Fe) grade of 20.78% in the ore was increased to 23.17% in the concentrate, while the average iron oxide (Fe2O3) grade of 29.73% in the ore was upgraded to 33.15% in the concentrate. The percentage increase in iron content from the initial ore grade to the final concentrate grade was calculated to be 11.5%. This means that the average iron concentration in the concentrate has increased by approximately 11.5% compared to the original ore. However, further separation is necessary to enhance the iron content and eliminate impurities to meet the minimum iron grade specifications needed for blast furnaces and steel manufacturers.