## 1 Introduction
Bentonite is basically an impure clay mainly consisting of montmorillonite mineral. Bentonite clay fulfills all the requirements of ASTMC-618C [33] to be used as a cement replacement material, as shown in Tables 1 and 2. Moreover, by heating this clay, its pozzolanic reactivity can be enhanced further compared to unheated condition [31; 34]. By using bentonite clay as a supplement to OPC, an eco-friendly, economical, and durable concrete can be achieved [3; 13]. Pozzolana can be activated by different methods; i.e., mechanical, thermal, and chemical activation. Mechanical activation means to ground the SCMs into powder form to increase their fineness and surface areas. Previous studies found that the pozzolanic reactivity of SCMs can be increased by mechanical activation (grinding) [35; 36]. As in a pozzolanic reaction, the silica (SiO\({}_{2}\)) part of pozzolan reacts with CH in the presence of moisture and forms CSH gel. It was reported that the pozzolanic reaction is determined by rate of dissolution of SiO\({}_{2}\) in water, and the dissolution rate of SiO\({}_{2}\) is proportional to its surface area [37; 38]. Despite increasing surface area prolonging the grinding of a material, it also increases the number of active centers at the edges of the material structure which are more energetic than the normal structure; the pozzolanic reactivity of the material depends on the number of active centers [39; 40]. Thermal activation means heat treatment (calcination). It can be heating of the pozzolan or the high temperature curing of the specimens made with pozzolans. It was reported that thermal treat of clays produce a metastable state due to structural disorder and an amorphous reactive structure is formed [41; 42]. Different clays have different calcination effects on their pozzolanic reactivities. [PERSON] et al. [43] studied thermal treatment effect on the pozzolanic reactivity of 70 different types of pozzolana and reported the optimum activation temperature range of 650-870 \({}^{\circ}\)C. In previous studies, the optimum activation temperature for Bentonite was reported as the range of 800-830 \({}^{\circ}\)C [28; 31]. In our previous research [34], the optimum activation temperature of the bentonite clay was found to be 800 \({}^{\circ}\)C.  
Many studies have been conducted in Pakistan for utilizing industrial wastes, such as bagasse ash [44], rice husk ash [45], fly ash [46; 47], etc., as SCMs. Some natural pozzolana have also been studied [3; 13]. In the existing literature, very few studies have been conducted to explore the potential of bentonite clay as partial replacement of cement. A study of bentonite on the mechanical and durability properties of concrete needs to be done in more detail. [PERSON] et al., [13] studied sawabi bentonite clay (3%, 6%, 9%, 12%, 15%, 18%, and 21% by mass) as an OPC replacement and reported positive results of bentonite on the fresh and mechanical properties of concrete. Also, further study was recommended [13] to explore the mechanical and thermal activation of bentonite clay and to study its effects on the properties of concrete. Moreover, high replacement levels of bentonite clay need to be explored. This study explored the mechanical and thermo-mechanical activation of bentonite clay to enhance its incorporation level in concrete. The performance of concrete was studied, both for \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Physical Properties** & **OPC** & **Bentonite** &
\begin{tabular}{c} **ASTM C618 Class N** \\ **Requirements (\%)** \\ \end{tabular} \\ \hline \% Retained \#325 mesh & - & 11.4 & 34 maximum \\ Blaine fineness (cm\({}^{2}\) g\({}^{-1}\)) & 3152 & 2571 & - \\ Specific gravity (g cm\({}^{-3}\)) & 3.05 & 2.81 & - \\ Average Particle size & 20 \(\mu\)m & 4 to 5 \(\mu\)m & - \\ Strength Activity Index & - & - & - \\ (\%) & - & 84.4 [34] & 75 minimum \\
28 days & - & 85.3 [34] & 75 minimum \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physical properties of ordinary Portland cement (OPC) and bentonite clay.