Available online at www.CivileJournal.org Civil Engineering Journal (E-ISSN: 2476-3055; ISSN: 2676-6957) Vol. 10, No. 04, April, 2024 1125 Properties and Microstructure of Treated Coal Bottom Ash as Cement Concrete Replacement Moad Alosta 1 , Ahmed Mamdouh 2 , Hussein Al Mufargi 1 , Farah N. A. Abd Aziz 2 , Ahmed Rashid 2 , Otman M. M. Elbasir 3 , Husam Al Dughaishi 1, 4* 1 Department of Civil and Environmental Engineering, College of Engineering, University of Nizwa, Ad-Dakhliyah, Oman. 2 Housing Research Centre, Department of Civil Engineering, Faculty of Engineering, Universiti Putra Malaysia, Serdang, Selangor, Malaysia. 3 Department of Civil Engineering, High Institute of Science and Technology, Qasr Bin Ghashir 22131, Libya. 4 Department of Civil Engineering, Faculty of Engineering, Universiti Malaya, Kuala Lumpur 50603, Malaysia. Received 05 December 2023; Revised 14 March 2024; Accepted 19 March 2024; Published 01 April 2024 Abstract Sustainable construction is a rapidly growing area of research focused on using industrial waste to replace Portland cement in concrete. This approach not only reduces CO2 emissions from cement production but also serves as an effective way to diminish the environmental impact of concrete production. This study aims to investigate the properties of Coal Bottom Ash (CBA) after undergoing two different treatments: flotation and burning. It also evaluates the impact of CBA as a cement replacement in concrete with different replacement percentages (5%, 10%, 15%, and 20%). Chemical analysis of CBA has revealed that it can be classified as a pozzolanic material due to its high content of silicates, aluminates, and iron oxides. The microstructure of CBA showed a porous, angular, and irregular surface with many voids. The findings of this study revealed that the optimum mix was 10% CBA, resulting in a 2% increase in compressive strength compared to the control mix after 56 days of curing. Additionally, the study evaluated the effects of sulfate and chloride on concrete. It was found that the mix with the burning treatment showed an overall increase in strength, while the flotation treatment did not reach the control mix's strength in any of the curing periods. Furthermore, the results demonstrated that CBA has significant potential as a cement replacement material, and the burning treatment showed improvement in concrete's overall properties compared to the raw material in terms of mechanical and chemical properties while reducing greenhouse gas emissions and enhancing the environment. Keywords: Industrial Waste; Material Properties; Coal Bottom Ash; Compressive Strength; Microstructure. 1. Introduction 1.1. Research Background Concrete is one of the most widely used and versatile construction materials in the world, capable of being molded into various shapes and sizes and known for its high strength and durability [1–3]. It is used to build structures, bridges, dams, and other infrastructure, including the Burj Khalifa, the tallest building in the world, which was constructed with 333,000 cubic meters of concrete [4–6]. However, concrete also has a significant environmental impact, as its main ingredient, Portland cement, accounts for about 8% of global CO2 emissions [7–10]. Furthermore, the production and disposal of concrete generate large amounts of waste and pollution. * Corresponding author: husam@unizwa.edu.om http://dx.doi.org/10.28991/CEJ-2024-010-04-08 © 2024 by the authors. Licensee C.E.J, Tehran, Iran. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).