## 1 Introduction  
In developing countries like Pakistan, the demands for housing and infrastructure development are increasing each day due to rapid urbanization and population growth. Being a major construction material, the demand for cement has increased abruptly in the recent past to fulfill the infrastructure needs. The production of cement exceeded 4.1 billion tons in 2018 alone, which makes it the most used material after water [1]. Large scale, global, ordinary Portland cement (OPC) production has always been a big threat to the environment, resources, and economy. Nowadays, cement manufacturing accounts for more than 5% of worldwide CO\({}_{2}\) emissions [2]. Moreover, the cost of cement has increased almost 150% in the short span of 10 years [3]. The use of supplementary cementitious materials (SCMs) as replacements of OPC is of great interest for limiting the environmental impact of construction industry [4; 5]. It is reported that CO\({}_{2}\) emissions can be minimized by replacing OPC with SCMs [6; 7; 8; 9]. SCMs, which do not require any additional clinker processing, can significantly reduce the CO\({}_{2}\) emissions per ton of cementitious materials [4]. The use of natural pozzolans in binder or concrete can result in various beneficial properties, such as low hydration heat, improved later-strength, low permeability, high sulfate-attack resistance, and low alkali-silica reactivity [10; 11]. It is estimated that concrete works in a building cost about 31% of the total, and OPC is the main cost-controlling constituent of concrete [12]. SCMs can be utilized for low-cost concrete construction as well [3; 13]. Different types of SCMs such as fly ash, bentonite, metakaolin, silica fume, calcined shale, etc., have been used to improve the performance of cement-based composites [14; 15; 16]. Till now, SCMs have been extensively used (60%) in ready-mixed concrete owing to their pozzolanic nature [17]. SCMs give comparable results in terms of mechanical performance and show outstanding performances in terms of durability [10; 18]. By blending SCMs with OPC, the penetration of harmful chemicals into concrete can be controlled. After the hydration of OPC, a primary by-product, calcium hydroxide (CH), is produced, which is the main target of corrosive media to deteriorate the concrete [19; 20]. Supplementary pozzolanic material consumes the CH during the pozzolanic reaction and forms additional calcium silicate hydrate (C-S-H) gel, leading to a durable concrete [21; 22; 23; 24; 25]. Pozzolanic cement blends show resistance to thermal cracking due to its low heats of hydration. Moreover, these blended cements have improved ultimate compressive strengths and low permeability because of pore refinement [20; 26; 27]. In certain locations, natural SCMs or pozzolans are abundant and widely used in countries such as Italy, Germany, Greece, and China as supplements to OPC [28]. Natural SCMs have a wider range of composition and larger variability in physical characteristics compared to traditional or industrial SCMs. The applications of natural SCMs are limited and controlled by their local availability and competition with the industrially produced SCMs (by-products). In future, the use of natural SCMs will expand more because of their extensive deposits all over the world and proven technical advantages [29]. Clay minerals are hydrous aluminum phyllosilicates, composed of repeated two dimensional, tetrahedral (T) and octahedral (O), sheets in different ratios [30]. The two sheets are hold together by an exchangeable interlayer cation coordinated to H\({}_{2}\)O molecules in the interlayer region. When T-sheets and O-sheets combine 2:1, the smectic group of clay minerals is formed. Bentonite clay (montmorillonite mineral) belongs to this group [31]. Bentonite is a natural pozzolana found in different regions of the world. The word bentonite was first proposed by [PERSON] in 1898 [32]. Bentonite is also found in different areas of Pakistan, including the province Khyber Pakhtunkhwa [13].