Research Article Fresh, Mechanical, and Microstructural Properties Investigation on the Combined Effect of Biomedical Waste Incinerator Ash and Bagasse Ash for High-Strength Concrete Menker Girma 1,2 and Belachew Asteray 2 1 Department of Construction Technology and Management, Institute of Technology, Debre Markos University, Debre Markos, Ethiopia 2 Department of Civil Engineering, College of Architecture and Civil Engineering, Construction Quality & Technology Center of Excellence, Addis Ababa Science and Technology University, Addis Ababa, Ethiopia Correspondence should be addressed to Menker Girma; menker.girma@aastu.edu.et Received 16 December 2021; Revised 23 March 2022; Accepted 20 April 2022; Published 31 May 2022 Academic Editor: Teresa M. Piqu Copyright © 2022 Menker Girma and Belachew Asteray. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. e 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. is 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. e cement was partially replaced with BA (0%, 2.5%, 5%, and 7.5%) and BWIA (0%, 2.5%, 5%, and 7.5%). e 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. e 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. e 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. e 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 mi- crostructure high-strength concrete. 1. Introduction Concrete is the most widely used construction material in the world because it is a multipurpose material that can be used to construct a variety of structures such as buildings, roads, dams, bridges, and so on. It is a composite material composed of Portland cement, coarse aggregate, fine ag- gregate, water, air, and occasionally used admixture [1, 2]. High-strength concrete is designed to greater compressive strength, flexural strength, and greater splitting strength than normal concrete. To create high-strength concrete that must meet performance criteria standards, superior mate- rials are employed. To produce high-strength concrete, special mixing, placement, and curing methods are required [3]. e assembly of concrete-making ingredients or ma- terials generally requires high cost and high energy and Hindawi Advances in Materials Science and Engineering Volume 2022, Article ID 5685372, 15 pages https://doi.org/10.1155/2022/5685372