Geopolymer synthesis using low-grade clays Morteza Tahmasebi Yamchelou a , David Law a,⇑ , Robert Brkljac ˇa b , Chamila Gunasekara a , Jie Li a , Indubhushan Patnaikuni a a Department of Civil Engineering, RMIT University, Victoria 3000, Australia b Monash Biomedical Imaging, Victoria 3168, Australia highlights  Compressive strength of up to 50 MPa is achievable using calcined low-grade clay.  The morphology of pores in untreated clay-based geopolymer was irregular.  Calcined clay-based geopolymer exhibits spherical pore distribution morphology. article info Article history: Received 24 May 2020 Received in revised form 16 September 2020 Accepted 18 September 2020 Available online xxxx Keywords: Geopolymer Low-grade clay Calcined clay Strength optimisation Energy-dispersive X-ray spectroscopy CT scan abstract Due to the large contribution of cement production towards CO 2 emission and rising concerns regarding climate change, substitution with alternative binders has become an established alternative to improve sustainability. Aluminosiliceous polymeric materials, known as geopolymer or alkali activated materials, have been proven to achieve a performance as good as and even superior to ordinary Portland cement (OPC). Various source materials have the potential to be used for the geopolymer synthesis depending on the local availability, among which fly ash, slag, and metakaolin have received most attention. A less established alternative is low grade clay, whether as the natural clay or the waste of construction work. These have the potential for geopolymer production due to their composition and abundance worldwide. However, due to the impurities present in these low-grade clays and slower dissolution rates, the synthe- sised geopolymers generally display lower mechanical performance. In this research, four different clays collected form construction sites in Melbourne, Australia, were characterised, and the optimum clay selected based on the amorphous content, specific surface area, and fineness. Furthermore, a relatively low energy-demand calcination regime was applied to the chosen clay, 550° C for 1 h. For the untreated clay-based geopolymer, a 7-day compressive strength of nearly 32 MPa was achieved, which increased to approaching 50 MPa after calcination at 550° C. A range of microscopy techniques, EDS, XRD, XRF, zetametry, 27 Al MAS NMR, and computerised tomography were applied to characterise the microstruc- ture and reaction kinetics of the synthesised geopolymer. Ó 2020 Elsevier Ltd. All rights reserved. 1. Introduction Geopolymer is a promising substitute for ordinary Portland cement (OPC), which is responsible for nearly 5% of the total indus- trial CO 2 emissions [1], with a potential to achieve up to an 80% reduction in CO 2 release [2,3]. A wide variety of materials can be used to make geopolymer, among which fly ash, slag, and metakao- lin have been extensively used [4–8]. Fly ash is one of the extensively used raw materials in the production of geopolymers. However, coal-based power plants are likely to be de-commissioned in the near future due to environmental issues. Therefore, the availability of fly ash for geopolymer synthesis may become an obstacle for large-scale geopolymer production. Clay is an alternative potential source for use in the production of geopolymer. Clay is a cheap resource and abundantly available worldwide, which would make it a reliable source for geopolymer synthesis. Some prominent studies on clay-based geopolymer are those of Davidovits. This research focused on the alkalination of kaolinite and the calcined counterpart metakaolin. Although this class of clayey minerals, which are referred to as 1:1 clay due to their tetrahedral and octahedral layers stacking order, exhibits good geopolymeric properties, their availability can be a barrier for the feasible large-scale synthesis of geopolymeric materials. https://doi.org/10.1016/j.conbuildmat.2020.121066 0950-0618/Ó 2020 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: david.law@rmit.edu.au (D. Law). Construction and Building Materials xxx (xxxx) xxx Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat Please cite this article as: M. Tahmasebi Yamchelou, D. Law, R. Brkljac ˇa et al., Geopolymer synthesis using low-grade clays, Construction and Building Materials, https://doi.org/10.1016/j.conbuildmat.2020.121066