Research Paper Hydrated lime/potassium carbonate as alkaline activating mixture to produce kaolinitic clay based inorganic polymer Muayad Esaifan a , Hani Khoury b, ⁎, Islam Aldabsheh b , Hubert Rahier c , Mohammed Hourani a , Jan Wastiels d a Department of Chemistry, The University of Jordan, Amman, Jordan b Department of Geology, The University of Jordan, Amman, Jordan c Department of Physical Chemistry and Polymer Science, Vrije Universiteit Brussel (VUB), Brussels, Belgium d Department of Mechanics of Materials and Constructions, Vrije Universiteit Brussel (VUB), Brussels, Belgium abstract article info Article history: Received 28 December 2015 Received in revised form 20 March 2016 Accepted 21 March 2016 Available online xxxx The stability as a function of storage time of an alkaline mixture developed by reacting hydrated lime (Ca(OH) 2 ) with a solution of potassium carbonate (K 2 CO 3 ) has been studied. The chemical and microstructure of alkali- activated kaolinite using the developed alkaline mixture were studied using XRD, ATR-FTIR, TGA and EDX-SEM. Over storage time of 24 h, the developed alkaline mixture was always composed of solid and liquid fractions. The solid fraction was characterized as a mixture of hydrated lime, butschliite (Ca 2 K 6 (CO 3 ) 5 ·6H 2 O) and calcite (CaCO 3 ), and the liquid fraction as a solution saturated with K + ions in a highly alkaline environment (OH − ). The inorganic polymer was dominated by hydrous phase of kaliophilite (K 2 Si 2 Al 2 O 8 ·3H 2 O), hydrated lime, butschliite and calcite. Different mixing procedures of water, hydrated lime and potassium carbonate with kaolinitic clay were used to produce an inorganic polymer, whose strength and stability were evaluated in terms of unconfined compressive strength under dry and saturated conditions. A maximum dry strength of 39 MPa and a maximum soaked and cycled strength of 11 MPa were obtained. A low cost-environment friendly alkaline mixture was developed to produce kaolinitic clay based inorganic polymer for construction and industrial applications. © 2016 Elsevier B.V. All rights reserved. Keywords: Alkali-activation Hydrated Lime Potassium carbonate Inorganic polymer Kaolinite Building material 1. Introduction Inorganic polymers (Duxson et al., 2007; Rahier et al., 1996) and geopolymers in particular (Davidovits, 1991) have been investigated in- tensively in last decades as alternative and green building materials in terms of low CO 2 emission, mechanical strength and durability (Bernal and Provis, 2014; Davidovits, 1991; Duxson et al., 2007; Esaifan et al., 2015; Pacheco-Torgal et al., 2008; Rahier et al., 1996). The class of inor- ganic polymers studied here is synthesized by alkali-activation of reac- tive aluminosilicate sources, starting from naturally abundant materials (e. g. kaolinite, volcanic tuff, etc.) (Esaifan et al., 2015; Lemougna et al., 2013; Slaty et al., 2013), and even waste or by-products (e.g. fly ash, blast furnace slag, etc.) (Wastiels et al., 1994; Song et al., 2000). The most used alkaline activating solutions are based on chemicals such as NaOH, KOH, and potassium or sodium silicate solutions (Pacheco-Torgal et al., 2008; Slaty et al., 2013). These chemicals are ex- pensive and aggressive when manipulated. This is one of the reasons for the slow commercial breakthrough of inorganic polymers. The use of Ca(OH) 2 instead of KOH or NaOH solutions could solve some safety is- sues. However, the use of pure Ca(OH) 2 results in poor mechanical prop- erties if the aluminosilicate source has no pozzolanic properties (Gogo, 1990; Shi et al., 2006). In early work, Gogo (1990) obtained improved mechanical properties with addition of K 2 CO 3 , but the results were not published in scientific literature. Only limited information is available about the system K 2 CO 3 /Ca(OH) 2 /H 2 O(Gogo, 1990). The idea behind mixing K 2 CO 3 and Ca(OH) 2 with the addition of water, is the partial dis- solution of Ca(OH) 2 and release of OH − . Gogo (1990) suggested that hy- drolysis and precipitation reactions occur in the K 2 CO 3 /Ca(OH) 2 /H 2 O system. A double salt, named butschliite (Milton and Axelrod, 1947; Mrose et al., 1966; Pabst, 1974), was formed next to CaCO 3 according to the following reactions: K 2 CO 3 þ Ca OH ð Þ 2 →2KOH þ CaCO 3 ð1Þ 8KOH þ 6H 2 O þ 6CaCO 3 →4Ca OH ð Þ 2 þ Ca 2 K 6 CO 3 ð Þ 5 Á 6H 2 O þ K 2 CO 3 : ð2Þ In this paper, first a more in depth study is carried out to better understand which reactions take place in the K 2 CO 3 /Ca(OH) 2 /H 2 O system. The aim is to study the chemical composition and stability of Applied Clay Science xxx (2016) xxx–xxx ⁎ Corresponding author. E-mail addresses: mu.esaifan@ju.edu.jo (M. Esaifan), khouryhn@ju.edu.jo (H. Khoury), islam.aldabsheh@gmail.com (I. Aldabsheh), hrahier@vub.ac.be (H. Rahier), mhourani@ju.edu.jo (M. Hourani), jan.wastiels@vub.ac.be (J. Wastiels). CLAY-03810; No of Pages 9 http://dx.doi.org/10.1016/j.clay.2016.03.026 0169-1317/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay Please cite this article as: Esaifan, M., et al., Hydrated lime/potassium carbonate as alkaline activating mixture to produce kaolinitic clay based inorganic polymer, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.03.026