Constructing and operating infrastructure facilities have traditionally been the responsibility of the public sector. Governments in several countries have been gradually enlisting the private sector in the provision of infrastructure through a public-private partnership. The purpose of this study is to investigate the reasons behind the potential implementation of public-private partnerships in Ethiopian road sector, which provide scientific support and rationales. There were both qualitative and quantitative research approaches used. A questionnaire survey was conducted, as well as an interview with industry professionals. To analyze the collected data, qualitative and quantitative data analyses were applied. The quantitative data were analyzed using version 26 of the Statistical Package for the Social Sciences software. The findings revealed scarcity in government funding, the inability of the public sector to assume all project risks, social strain on people due to poor road facilities, the demand for the skills and experience of the private sector, and the requirement for improvements in the levels of services as leading reasons for the potential implementation. The findings of the study provide scientific data and support for the adoption of public-private partnerships as they give solutions to the problems associated with road infrastructure delivery.
With the development of cracks on their surfaces, mortar’s service life dramatically shortens. Self-healing concrete by Microbiologically Induced Calcite Precipitation (MICP) is one of the high-tech concretes being used to address these issues. This type of mortar can start biological processes to repair itself and deal with its cracks. The self-healing effectiveness of two different bacteria, in this paper, Bacillus subtilis and Bacillus cereus, added to the mortar is examined experimentally. In order to conduct this investigation, artificial cracks were made in the mortar. A 3D optical microscope was used to take repeated pictures of the cracked mortar. The mechanical and durability tests conducted on the bacterial mortar were used to gauge the efficacy of self-healing. Mortar samples were left for 7, 14, and 28 days to cure. Compressive strength, flexural strength, water absorption, and sorptivity were measured during various times of the curing process. The test results showed that the mortar with bacteria had an increase in strength and durability compared to the control mix. In the sample of mortar containing bacteria, Bacillus subtilis and Bacillus cereus a maximum increase of 17.29% and 11.31% in flexural strength, 17.77% and 12.84% in compressive strength were observed and a 34.48% and 26.43% decrease in water absorption in the mortar sample containing bacteria, Bacillus subtilis and Bacillus cereus at 28 days, respectively. The results of the mortar absorption test showed that the addition of bacteria to the mortar matrix significantly reduced the primary and secondary absorption rates of bacterial mortars B-M-1 and B-M-2. Using a 3D light microscope, the cracks in the bacterial mortar showed that larger amounts of white crystal precipitates were generated that nearly filled the surface of the crack. Overall, Bacillus subtilis appeared to be superior to Bacillus cereus based on the results of mechanical and mortar durability tests because calcium carbonate precipitates more rapidly.
The combination effect of supplementary cementitious materials in the production of high-strength concrete production is an effective way to reduce the amount of cement required while contributing to environmental sustainability and cost. This study aims to assess the microstructural investigation on the combined effect of biomedical waste incinerator ash (BWIA) and bagasse ash (BA) as a partial replacement of cement in high-strength concrete production. The cement was partially replaced with BA (0%, 2.5%, 5%, and 7.5%) and BWIA (0%, 2.5%, 5%, and 7.5%). The mix design was done as per the ACI 211-4R-93 mix design standard. Slump, slump flowability, density, and compaction factor tests were conducted for freshly mixed concrete. Mechanical properties of the hardened concrete from four different mixes were also determined for the 7- and 28-day cured specimens. The microstructural properties of the hardened concrete for all mixes were also investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. Based on the experimental results, the compressive strength of high-strength concrete at every 2.5% BA and 2.5% BWIA replacement of cement in the concrete mix at 7 days of curing was slightly decreased, while at 28 days of curing, the compressive strength of the control mix (51.8 MPa) decreased as compared to the mix codes' compressive strength of the BWIA and BA5 and BWIA and BA10 mix codes, at 54.8 MPa and 52.5 MPa, respectively. The SEM micrographs showed that the partial replacement of cement by the BWIA and BA leads to a decrease in the pore proportion in the enlarged interfacial transition zone (ITZ), reduced CH crystals, and a denser C–S–H gel as compared to the control specimen. The XRD pattern showed the existence of portlandite, ettringite, okenite, quartz, and calcite in the cement and aggregate phases. As a result, the usage of BWIA and BA has a significant impact on the properties of high-strength concrete in fresh, hardened, and microstructure high-strength concrete.
This research focuses on studying the effect of different supplementary cementitious materials (SCMs) such as waste ceramic powder (WCP), lime powder (LP), and ground granulated blast furnace slag (GGBS) in combination on strength characteristics and microstructure of quaternary blended high-strength concrete. To achieve the aims of the study, necessary physical and chemical composition tests were done for the raw materials. Then, mixes were designed into control mix with 100% Ordinary Portland Cement (OPC) and experimental mixes containing 30%, 40%, 50%, and 60% of GGBS, WCP, and LP in combination. Tests were conducted during casting and at curing ages of 7 and 28 days. Accordingly, the control mix which is concrete grade 50 (C-50) as per American Concrete Institute (ACI) mix design is used as a reference for comparison of test results with those specimens produced by partial replacement of SCMs. The characterizations of high-strength concrete are done using consistency, setting time, workability, compressive strength, flexural strength, and morphological tests. The optimum percentage replacement is 50% OPC replacement by 30% GGBS + 10% WCP + 10% LP. Based on the experimental investigations, the workability increases as the replacement level of SCMs increases from 30% to 60% by weight. Compressive strength and flexural strength results increase up to 11.41% and 20% when the percentage replacement increases from 30% to 50% of SCMs replacement at 28 days of curing time, respectively. There are also improvement in the microstructure and significant cost saving due to replacing OPC partially with SCMs with proportions mentioned above. Therefore, the practice of utilizing increased percentage of SCMs in quaternary blend in concrete can be beneficial for the construction industry and sustainability without compromising the quality of the concrete product.
Congestion and extended passenger waiting time are some of the key issues that the Addis Ababa Light Railway Transit service (AALRT) faces. Passengers waited an average of 14.33 minutes, resulting in congestion of passengers. This is why the study set the main objective to develop an optimization model for improving AALRT service. The study began by developing the characteristics of the data to evaluate the congestion problem as part of its approach to achieving this objective. Second, on the selected station, an optimization model was constructed. Then an alternate model has been created by evaluating the previous model’s performance. Finally, without expanding the system, the researcher evaluates its effective service life. Using a combination of queuing theory and Monte Carlo simulation approach, the study used case study research methodology by taking the most congested metro station in both corridors and directions of AALRT at peak hours. Primary data were collected from each station and the relevant authority, while secondary data were conducted from the literature. The finding indicates that the congestion rate of AALRT reaches up to 25.3% and the percentage of the extra capacity of the tramcar required up to 115%. Therefore, it was found that currently adding two single tramcars could reduce the waiting time up to 9.52 minutes and the congestion up to 99%. The new model indicates the company can improve the service by increasing the number of tramcars per hour and replacing single tramcars with double tramcars up to the year 2047 without expansion of the infrastructure.
Addis Ababa road construction projects fail to be executed on time, within the allocated budget, and with the desired quality. To solve this problem, a new management concept is introduced, namely, lean construction. It is known to increase productivity and minimize waste. And, to realize this solution, last planner system (LPS) is used; it is a tool of lean construction and it involves a person or group of people with the task to control the production unit. The objectives of this study are to examine the current construction process management practice in Addis Ababa city road construction projects, to identify and prioritize the expected barriers of the last planner system implementation in Addis Ababa road construction projects using the super decision model, to identify and prioritize last planner system implementation benefits to Addis Ababa road construction projects using the super decision model, and to develop a conceptual framework for the last planner system implementation to enhance the current construction management system in Addis Ababa city road construction projects. To address the problems, questioners, observations, interviews, focus group discussions, and recently published journals were employed as qualitative and quantitative data collection tools and analyzed using statistical package for the social science version 26 and super decision model version 3.2. The finding shows that the construction management process adopted in all three sites is more or less similar, as they use a push planning system and critical path method to determine the duration following the master schedule but have no weekly work plan and lookahead schedule to forecast the coming week’s duty; also, they use a push planning system, for materials. The LPS implementation expected barriers are also ranked from one to five: Labor related, internal working environment related, stakeholders related, exogenous related, and material related expected barriers, respectively. The last planner system has many benefits as agreed by different scholar. Time-related, cost-related, claim-related, and quality-related benefits are the main benefits obtained through the LPS implementation, and it is possible to conclude that LPS is useful for road construction management process. Moreover, the LPS implementation conceptual framework was also developed based on the last planner system principles.
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