## 1 Introduction  
The ordinary Portland cement (OPC) has been used as a major ingredient for construction activities worldwide, which is generally used as a binder in the concrete [1, 2]. The ecological benefits and engineering properties of concrete have been improved by geopolymers, an alternative for the OPC/conventional concrete [3, 4]. The geopolymer concrete (GPC) possesses good engineering properties with reduced emission of greenhouse gases and is also known as green concrete [5]. GPC can not only lessen the carbon footprint associated with OPC but can also use a bulk quantity of industrial by-product/waste materialssuch as fly ash (FA), blast furnace slag (SG), ceramic wastes, and silica fumes, etc. [5; 6; 7; 8]. The waste materials such as FA, rice husk ash, SG, metakaolin, mine waste, silt, tungsten, iron, copper and gold ores, marble, and some industrial by-products are a promising hazard to the environment. Fossil fuels are used in thermal power plants to generate electricity that produces a significant quantity of FA wastes, about 800 million tonnes globally [9], out of which only a minor portion (20-30%) is used [10]. The improper dumping of this residue causes environmental issues such as water and air pollution. Some of these materials can be used as building materials, thus reducing landfill costs and protecting the environment from harmful effects. Therefore, GPC has been under study due to its relatively better mechanical properties and environmental benefits. The polymeric materials are inorganic and produce geopolymers by the polymerization of aluminosilicates with alkaline solutions that harden and strengthen at ambient temperatures [11]. The GPC has two main constituents other than the aggregates: aluminosilicate source materials and an alkaline activator solution (AAS). The most used alkaline activator is a combination of sodium silicate (SS) and sodium hydroxide (SH) solutions, though potassium hydroxide and potassium silicate can also be used. AAS plays an important role in the polymerization process [12]. The source binder materials in a GPC must have silicate and aluminate in a significant amount. The use of local raw materials is an important consideration and is suitable for an economical and geofriendly environment. The benefits of using local raw materials include low transportation cost, low amount of energy for transportation, better overall control, and reduced emissions and energy usage. The local natural sources of aluminosilicate materials are bentonite and metakaolin clay, mine waste, silt, tungsten, iron, copper and gold ores, etc. [6; 7; 8; 13], whereas the waste by-product materials FA [14; 15], SG [16], ceramic wastes, and silica fumes [17], etc., can be used for the preparation of geopolymer concrete due to their abundant availability. The selection of source materials for making GPC depends on numerous factors including availability, cost, and applications [18]. Most researchers have worked on the development of GPC with heat curing [19; 20]. The FA has been used as an appropriate raw material for GPC due to its wide range of availability and suitable composition of alumina and silica. The previous studies [19; 21] have described that FA-based GPC has good durability and mechanical properties after heat curing at 60 to 85 \({}^{\circ}\)C. At ambient temperature, the reaction process of FA is too slow [15]. The heat curing conditions are generally appropriate for industrial precast constructed members and usually cannot be practiced for cast-in-situ construction. Hence, it is important to develop a type of GPC without heat curing to expand its field and site application. This can further reduce the cost and energy consumption linked with the elevated temperature curing. A few studies have tried to improve the reactivity of FA by varying the SS/SH ratios, alkaline activating content, and molarity of SH to achieve good results at the ambient curing conditions [22]. One of the acceptable methods is to add calcium-rich materials such as SG in GPC at ambient curing conditions.