# Low-Grade Clay as an Alkali-Activated Material
## 1 Introduction  
Alkali-activated materials (AAMs) have come in to use as substitute materials for ordinary Portland cement (OPC) in the construction industry in recent years. The use of AAM not only limits the emissions of contaminants but also consumes less energy and, thus, can play a major role in reducing the global warming problem [1, 2, 3, 4, 5]. Different types of raw materials, such as fly ash, kaolinite, palm oil fuel ash, rice husk ash, shale, natural zeolite, types of sludge, lignite bottom ash, natural fibers, red mud, and clay and clay minerals (including bentonite and montmorillonite), are currently being investigated as possible AAMs. Studies have shown that concrete made from different industrial waste material can display comparable or even better mechanical and durability properties than those associated with OPC concrete [6, 7, 8, 9, 10, 11, 12, 13, 14]. According to the reports of the Intergovernment Panel on Climate Change [3, 15], the growth of world cement production increased sevenfold by 2010 compared to that in 1970, and from 2000, this growth has been increasing sharply driven by demand from the construction industry. It has been also reported that the cement industry was responsible for more than 13% of global emissions (emissions from cement-forming reactions only) of CO\({}_{2}\) in 2010. The IPCC has also suggested using geopolymer concrete in place of OPC concrete to reduce CO\({}_{2}\) emissions. Research conducted to date has primarily focused on fly ash as a primary source of binder material. A concern is that fly ash production will decrease in the future as power generation switches from coal to other renewable forms of electricity production. It has alsobeen reported that not all fly ash is suitable for geopolymer concrete production. Low-grade clay, which is a naturally occurring material that is abundant throughout the world, could be a suitable alternate source material to fulfil this requirement. [PERSON] et al. suggested that there was the potential for global warming to be reduced by up to 40% if alkali-activated clay was used in place of OPC [4]. [PERSON] et al. also identified the necessity for alternate substitute source materials for the production of geopolymer concrete [16]. [PERSON] et al. assessed the performance of uncalcinated montmorillonite and illite clays and reported a large variation in the properties, with montmorillonite displaying the more promising behavior [13]. [PERSON] et al. investigated the long-term durability of alkali activation of soil samples with 13% clay particles, and the alkali-activated material demonstrated improved mechanical performance [14]. However, research on the utilization of low-grade clay as an alternative material for geopolymerization system is still in its infancy. Research into clay-based geopolymers has reported strengths in the range of 5-40 MPa [17; 18; 19; 20; 21; 22; 23]. Calcination has been widely adopted to increase the reactivity of clay, utilizing temperatures up to 1000 \({}^{\circ}\)C [24; 25; 26]. Mechanical activation has also been proposed to increase reactivity, but the research is not as extensive [27; 28]. A number of researchers have reported that reactivity increases due to the pre-heat treatment. [PERSON] and [PERSON] noted that the crystalline phase is transformed into the reactive amorphous phase due to heat treatment [29]. However, if too high, the applied calcination temperature may result in the formation of new crystalline phases that are not reactive [30]. [PERSON] et al. reported that the reactive amorphous phase becomes unreactive if the pre-treatment temperature is over 900 \({}^{\circ}\)C [31; 32], while [PERSON] et al. stated that applying a pre-treatment temperature of up to 850 \({}^{\circ}\)C does not have a significant effect on the properties of geopolymers [33]. [PERSON] and [PERSON] stated that the reactivity of calcined clay to be used is dependent on the duration of calcination [34].