@article{Khalifa_Pontikes_Elsen_Cizer_2019, title={Comparing the reactivity of different natural clays under thermal and alkali activation}, volume={4}, url={https://letters.rilem.net/index.php/rilem/article/view/85}, DOI={10.21809/rilemtechlett.2019.85}, abstractNote={<p>Metakaolin is one of the most popular solid aluminosilicate precursors for the synthesis of geopolymers. Despite its high reactivity and availability, there is a noticeable move towards the use of other natural clays as alternative precursors, due to their plentiful supply and widespread availability. Natural clays usually consist of a combination of 1:1 and 2:1 layer silicates reactivity of which vary. In this work, four different natural clays (SS, BS, MS and WS) composed of 1:1 and 2:1 clay minerals at different proportions were studied for the synthesis of geopolymers. To increase their reactivity prior to alkali activation, the clays were calcined in a laboratory oven at different temperatures (700, 750, 800, 850, 900 °C) and different holding times (10 seconds to 60 minutes). The reactivity of the calcined clays was assessed by the dissolution test and isothermal conduction calorimetry. NaOH and a mix of NaOH and Na<sub>2</sub>SiO<sub>3</sub> were used as alkaline activators. The results show that the optimum calcination temperature of SS, BS and MS is 800 °C with a holding time of 10 minutes. WS is sufficiently calcined at a higher temperature of 900 °C for 20 minutes. Kaolinite-rich clays (SS) present more reactivity towards alkali activation than clays dominated by smectite or illite.  </p>}, journal={RILEM Technical Letters}, author={Khalifa, Ahmed Zohair and Pontikes, Yiannis and Elsen, Jan and Cizer, Özlem}, year={2019}, month={Nov.}, pages={74–80} }