Effect of Elevated Temperature on Microstructural and Durability Properties of High-Strength Concrete-Containing Eggshell

Researchers have recently discovered that eggshell contains a significant amount of calcium carbonate through the characteristics of both fresh and hardened concrete by partially substituting cement with eggshell powder (ESP) at room temperature. The objective of this experimental investigation was to examine the microstructural and durability characteristics of high-strength concrete exposed to elevated temperatures using ESP as partial cement replacement. The impact of elevated temperature intensity (200, 400, 600, and 800°C) for one hour of exposure on the specimens and natural air-cooling method was studied. Various ESP cement blending percentages (0%, 5%, 10%, and 15%) were examined through different microstructural and durability tests such as workability, fire resistance, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and 3D optical surface profiler, air content tests, ultrasonic pulse velocity, weight loss, spalling and color changes, water absorption, and acid attack experimental tests. According to the findings, the amount of ESP exceed 5% replacement reduces the workability of fresh concrete mixtures. The best performance was reached by a mixture comprising 5%ESP specimens, with values of 63.41 and 64.07 MPa at ambient and 200°C, respectively. SEM results of 5%ESP at 200°C illustrate a decrease in the occurrence of pores and act as a bridge to form crystals between CH and C─S─H. The XRD result also indicates a high amount of jennite (C─S─H gel) was formed at 200°C due to the melting of ESP, which densifies the crystal of C─S─H. Regression analysis provided a more reliable expression for the relationship between the residual compressive strength and UPV with R2 values of 0.9833 and 0.9966 for control and 5%ESP mixes, respectively. As a result, it was determined that concrete with 5%ESP as a partial cement replacement performs better over time than control concrete and has the potential to be used in construction

An integrated Delphi and Fuzzy AHP model for contractor selection: a case of Addis Ababa Design and Construction Works Bureau

AbstractContractors fail to meet project objectives for a variety of reasons. One of the major reasons for this has been attributed to the current criteria for awarding contract ineffectiveness in identifying contractors capable of meeting today’s demands and challenges. Therefore, there is a need to develop alternative contract-awarding systems for public building construction projects. Thus, the purpose of this study is to develop multiple contractor selection criteria and a selection model by integrating the Delphi and Fuzzy AHP methods. First, this study conducted an extensive literature review of related studies to determine the contractor selection criteria to select contractors for building projects. Thirty sub-criteria were finalized under six major criteria categories, such as Bid Price, Financial Capacity. Technical Capacity. Management Capacity, Experience and Reputation, and Health, Safety and Environment. Two rounds of the Delphi method were then employed to finalize and categorize the contractor selection criteria. Finally, the Fuzzy AHP method was employed to assign weights to the contractor selection criteria and then rank them according to their importance. The study revealed that among all sub-criteria, Bid Price, Projects completed on time and within budget; Experience on Similar types and sizes of projects; and Qualification, Number and Experience of Staff are the most important selection criteria. The last four sub-criteria in the row with slight weight differences are innovative methods, liquidity, credit rating, and organizational structure. The results of this study serve as a benchmark for the application of multiple contractor selection criteria procurement in Ethiopia, and as a basis for future research