Effect of Cooling Rate on the Performance of Fired Geopolymer Paste *Hala E. Fouad,***Waleed H. Soufi,*Ahmed S. Elmannaey,**Magdy Abd-El-Aziz,**Hany EL-Ghazaly Faculty of Engineering – Misr University for Science and Technology * **Department of Civil Engineering -Faculty of Engineering - Fayoum University ***Housing and Building National Research Center (HBRC), Cairo, Egypt Abstract - One of the major drawbacks of Ordinary Portland Cement (OPC) products; paste, mortar and concrete, is its performance under the effect of elevated temperatures, especially if it is suddenly cooled after exposure to fire. Seeking a durable fire-resistant material is highly demanded. In this paper, the effect of cooling rate on compressive strength and mineral composition of geopolymer paste (made from slag base material and also a combination of slag, red mud and/or meta-kaolin) is addressed. All the results are compared to OPC paste. The compressive strength of the geopolymers prior to firing shows significantly higher strength. After exposure to fire (up to 900 o C), OPC and slag geopolymer paste has shown degradation in compressive strength regardless cooling rate. While, slag geopolymers with partial replacement had shown better performance with temperature increase regardless the cooling rate. In general, geopolymer pastes have shown formation of very stable mineral composition phases after exposure to elevated temperatures. It can be concluded that slag geopolymer pastes with partial replacement represent an excellent fire-resistant material. I. INTRODUCTION Geopolymers are inorganic polymers that are produced by the reaction of aluminosilicate source materials (i.e. red mud, metakaolinite, fly ash, blast furnace slag, waste glass, rice husk ash, etc.) and high alkalinity aqueous solutions (mainly sodium and potassium based materials). The reaction via a polymerization mechanism forms a solid cementitious material[1]. Molecular structures of any binder material are stable at ambient temperatures. This stability is affected when the temperature conditions change. Exposure time and heating rates are also important parameters which may lead to micro cracks and failure of the material in fire or elevated temperatures. OPC binder goes through a degradation process called spalling, where the cracks take place at surface and the paste deteriorates and breaks into smaller pieces around temperatures of 300 ○ C and 450 ○ C [2-4]. Geopolymers are generally believed to provide good fire resistance due to their ceramic-like properties[5]. The previous studies that investigated the thermal properties of the slag geopolymers have reported that these materials possesses low thermal shrinkage and good strength after exposure to high temperatures [6]. Other studies on fly ash geopolymer paste reported that it has high compressive strength prior firing but, after firing at 800 o C, these geopolymers lose its strength and fail [7]. Another study stated that geopolymer beams can successfully retain about 67% of its original flexural strength after a simulated large fire [8]. It can be concluded from the literature that this subject is still in need to more investigation to accurately assess which type of geopolymer pastes is the most durable fire-resistant. In this paper, Ground Granulated Blast Furnace Slag (GGBFS) geopolymer pastes were studied. Also, GGBFS base material was partially replaced by Red Mud (RM) and/or Meta-Kaolin (MK). A number of geopolymer mixes were chosen based on compressive strength results and their mineralogical compositions were assessed. The selected samples were also subjected to elevated temperatures (to simulate fire effect). After that, these samples were cooled even gradually in oven (after switching of the heater) or suddenly by soaking in water. The main objective of this paper is to investigate the effect of cooling rate; either gradual or sudden, on the mineralogical content and compressive strength of geopolymer pastes. Also, OPC samples were tested under the same procedure to compare the performance of geopolymer and OPC pastes under the effect of fire. 2. EXPERIMENTAL PROGRAM 2.1. Materials 2.1.1. Base materials The base materials used in the present study are GGBFS, MK and RM. These materials are available in the Egyptian market. GGBFS is an industrial by-product resulting from rapid water cooling of molten steel. This material is available in Iron and Steel Factory, Helwan Governate. Kaolin contains hydroxyl ions that are strongly bonded to the aluminosilicate framework and can only be altered by the temperature above 750 °C to be MK [9, 10]. At this high temperature, its atomic structure is rearranged to form partly ordered system with a great reaction potential to alkaline solutions. MK used in this study is obtained from an open query located in Sinai by Middle East Mining Company (MEMCO). RM can be defined as defected and crushed fired clay bricks. RM used in this study is obtained from clay brick factories, Helwan Governate. The X-Ray Fluorescence (XRF) analysis was utilized to determine the oxide composition for these materials in addition to OPC. All these materials contain Aluminate (Al) and Silicate (Si) compounds with various amounts, as shown in Table (1). By inspecting the results of table (1), it is obvious that all base materials are rich in SiO2 and Al2O3 in comparison to OPC. International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 http://www.ijert.org IJERTV6IS040123 (This work is licensed under a Creative Commons Attribution 4.0 International License.) Published by : www.ijert.org Vol. 6 Issue 04, April-2017 114