Study on mechanical properties of kaolin-based geopolymer with various Si/Al ratio and aging time
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ORIGINAL ARTICLE
Study on mechanical properties of kaolin‑based geopolymer with various Si/Al ratio and aging time Binghuan Gao1 · Seongwan Jang1 · Hyeonjin Son1 · Hee Jung Lee1 · Hwan Jong Lee2 · Jeong Jik Yang2 · Chang‑Jun Bae1 Received: 30 March 2020 / Revised: 14 July 2020 / Accepted: 10 August 2020 © The Korean Ceramic Society 2020
Abstract Geopolymers are a class of aluminosilicate-based ceramics that contain 3D network synthesized by condensation of tetrahedral aluminosilicate units, produced by the aluminosilicate raw materials and alkaline activators. The Si/Al ratio and aging time are the crucial parameters which influence the reaction degree of geopolymerization process and the reaction time, affecting the final properties, respectively. Here, we investigated the effect of Si/Al ratio and aging time on the microstructure and mechanical properties of kaolin-based geopolymers, where SEM, XRD, and piston on three ball test were applied at the different Si/Al ratio and the aging time. Given the higher ratio of Si/Al and longer aging time, geopolymer-based matrix was densified and high crystalline phases were evolved. Furthermore, the highest flexural strength of specimen, with the Si/ Al ratio of 2.49 and aging time of 1 day, was 19.5 MPa. Keywords Geopolymer · Si/al ratio · Flexural strength · Aging time
1 Introduction Geopolymer has been popularized on the new research hotpot in the past decades with its unique advantages such as high mechanical property, high corrosion resistance, high thermal stability, durability, waste recycling, low CO2 emission, and environmental protection [1–3]. Since Davidovits [1] reported the new terminology in 1989, many researchers have studied the mechanism, novel properties, and new applications of geopolymers. The material is composed of the 3D inorganic network structure produced by the dissolution and condensation process of raw materials that contain aluminosilicate components and alkaline activators. Si- and Al-rich materials have been widely used as the source materials to produce geopolymers, which undergo geopolymerization [4] process to transform from an amorphous to semi-crystalline structure with high mechanical strength when the source materials react with alkaline * Chang‑Jun Bae [email protected] 1
3D Printing Materials Center, Korea Institute of Materials Science (KIMS), Changwon 51508, Republic of Korea
Korea Automotive Technology Institute, Gyeonggi 15041, Republic of Korea
2
activators. In general, the source materials include not only the natural resources like kaolinite, mud, and clay, but also the industry wastes like F-fly ash, furnace slag, and steel slag. Depending on the raw material selection and processing conditions, geopolymers can exhibit a wide variety of properties and characteristics. Generally speaking, the properties of geopolymers are dependent largely on the composition of the reactants, especially the Si/Al ratio, which determines the application fields of geopolymers, as shown in Table 1 [5] Low Si/Al ratio (Si/Al ≤ 3) r
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