Investigation of the Potential Use of Heavy Oil Fly Ash as Stabilized Fill Material for Construction Abdullah Mofarrah 1 ; Tahir Husain 2 ; and Ekram Yousif Danish 3 Abstract: The present study investigates the use of heavy oil fly ash (HOFA) generated in the power plants as a stabilizer or fill material for various construction activities. To recycle the HOFA as fill material, it was mixed with Portland cement at different ratios. Laboratory batch and column experiments were performed on the HOFA and fill materials to investigate the leaching behavior and possible environmental impacts of the potentially hazardous elements such as arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), mercury (Hg), nickel (Ni), lead (Pb), copper (Cu), zinc (Zn), selenium (Se), and vanadium (V) within the HOFA. The results showed that leaching of toxic elements from the HOFA can pose toxicity to the environment, Whereas stabilized material prepared by HOFA mixed with 40% cement proved environ- mentally safe for construction uses. DOI: 10.1061/(ASCE)MT.1943-5533.0000442. © 2012 American Society of Civil Engineers. CE Database subject headings: Fly ash; Trace elements; Environmental issues; Fills; Construction materials. Author keywords: Heavy oil fly ash; Trace elements; Environmental impact; Soil fill material. Introduction Attributable to local availability and relatively low cost, heavy fuel oil is used in most of the power generation facilities in Saudi Arabia. About 320 million barrels of crude oil is annually used for power generation (Break-Bulk Online News 2010), which pro- duces approximately a quarter of a million tons of heavy oil fly ash (HOFA). In Saudi Arabia, it is anticipated that an increasing amount of HOFA will be produced from power plants firing crude and heavy fuel oils. Therefore, power plants in the Kingdom may face difficulties concerning the disposal of the produced HOFA. The current industrial management practices of HOFA in the Kingdom are mainly landfill disposal. Land disposal of fly ash is not a solution; it only creates ever-growing environmental problems. The research of the physical and chemical properties and possible applications of HOFA are still insufficient in the scientific literature. HOFA is a byproduct generated from the burning of heavy fuel oil. During the combustion of fuel oil in boilers, oil drops are heated and burned with oxygen and then depleted; at the same time, the impurities, such as sulfur, vanadium, and nickel within the fuel oil also undergo transformations and react with gaseous hydrocarbons to form particulates, known as ash (Masdin and Foster 1960; Sakai and Sugiyama 1970; Turner and Steve 2009). Burning fuel oil yields approximately 3 kg of ashes per kiloliter of oil (Tsai and Tsai 1997) and most of the ashes (approximately 90%) are fly ash, which is collected by electrostatic precipitators or cyclones for final disposal or use (Hsieh and Tsai 2003). The HOFA consists of inorganic substances such as silicon dioxide (SiO 2 ), iron oxide (Fe 2 O 3 ), aluminum oxide (Al 2 O 3 ), and 70–80% unburned carbon (Kwon et al. 2005). The HOFA contains a good percentage of valu- able metallic compounds such as 20–30% vanadium and 0.8–6% nickel (Zhang et al. 1995; Lozano and Juan 2001). The HOFA also contains heavy metals such as arsenic (As), cadmium (Cd), mercury (Hg), and copper (Cu), which exist in the crude petroleum at the outset, and their level increases during incineration (Hwang et al. 1996). The poor management and uncontrolled disposal of HOFA may cause dispersion of toxic pollutants which are hazardous to human health and environment (Fernandez et al. 2003; Choi et al. 2002). The hazardous elements (e.g., toxic metals) from HOFA dumping could be leached into surroundings by rainwater or acid rain, which might result in toxicity to the ecosystems and humans through con- tamination of surface and groundwater (Binner et al. 1997). The characteristics study of HOFA (Hsieh and Tsai 2003) showed that it could be considered fit for a variety of uses: from fill/stabilize material for construction or as an adsorbent for industrial pollutions control. The main goal of the present study is to use HOFA as fill material in construction activities and to decrease the amount of fly ash stored, because it represents a significant danger to human and ecosystem health. Leaching tests are generally used to evaluate the worst case environmental scenario of the solid waste (Querol et al. 1996; Praharaj et al. 2002; Fytianos et al. 1998). The main beliefs of these tests are to investigate whether some target compound will leach out from solid waste under specific leaching conditions. Solid waste management often requires interpretation of the leachability of toxic elements to assess the risk of dumping to human health and environment (Scott et al. 2005). Many leaching test protocols such as toxicity characteristic leaching procedure (TCLP), multiple extraction procedure (MEP), equilibrium leach test (ELT), acid neutralization capacity (ANC), and column leaching tests have been cited in literature (USEPA 1989; ECAEC 1986; Wang et al. 2008). These tests are developed to simulate the leaching processes of waste materials in 1 Dept. of Civil Engineering, Faculty of Engineering and Applied Science,Memorial Univ., St. John’ s, NL A1B 3X5 Canada (corresponding author). E-mail: abdullah.mofarrah@gmail.com 2 Dept. of Civil Engineering, Faculty of Engineering and Applied Science, Memorial Univ., St. John’ s, NL A1B 3X5 Canada. E-mail: thusain@mun.ca 3 Assistant Professor, in the Chemistry Dept. at King Abdulaziz Univ., Jeddah, Saudi Arabia. E-mail: ekydanish@yahoo.com Note. This manuscript was submitted on March 25, 2011; approved on December 7, 2011; published online on December 9, 2011. Discussion per- iod open until November 1, 2012; separate discussions must be submitted for individual papers. This paper is part of the Journal of Materials in Civil Engineering, Vol. 24, No. 6, June 1, 2012. ©ASCE, ISSN 0899-1561/ 2012/6-684–690/$25.00. 684 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JUNE 2012