## 1 Introduction
A geopolymers is generally formed through the following four steps: (a) Aluminum silicate mineral powder is dissolved in alkaline solution; (b) the dissolved silicon and aluminum ions diffuse from the solid particle surface to the particle pores; (c) the alkali-metal-silicate solution undergoes polymerization with silicon and aluminum ions; (d) the gel gradually removes the remaining water and solidifies into an aluminosilicate geopolymer [30]. Its structural composition differs from that of OPC formed through the pozzolanic reaction in that OPC uses the calcium silicate produced after the pozzolanic reaction to form a calcium-silicate-hydrate (C-S-H) colloid through hydration bonding, whereas a geopolymer uses the hydroxyl ions in a strong alkaline solution to precipitate the Si and Al atoms within the aluminum silicate, using the chemical bonding of their ionic states to form Si-O-Al-O polymeric bonds. Although geopolymers have considerable feasibility for replacing cement, the material is susceptible to temperature [31], curing environment [32] and different types and mixing concentrations of alkali activators [33; 34], which will affect the strength of the geopolymer. A low-concentration alkali activator produces a geopolymer with lower structural strength and a slower hydration rate; although a high-concentration alkali activator can increase structural strength and accelerate coagulation, it will also produce fragile specimens that weather and break easily [35]. A more active material, coupled with a longer mixing time, will increase its compressive strength and ion dissolution, which contributes to more intense polymerization. An increase in L/S will dilute the concentration of the alkali equivalent and decrease its pH value and the amount of hydroxide, whereby the compressive strength decreases because of the inability to precipitate the silicon and aluminum elements. [PERSON] et al. [36] found that the optimal geopolymer was prepared with metakaolin, sodium hydroxide, sodium silicate and water, with the molar ratio of SiO\({}_{2}\):Al\({}_{2}\)O\({}_{3}\):Na\({}_{2}\)O:NaOH:H\({}_{2}\)O being 3.4:1.1:0.5:1.0:11.8. With further investigation using their advantageous characteristics (i.e., high strength, heat and chemical attack resistance and low thermal conductivity), geopolymers are likely to replace cement as a next-generationconstruction material. Based on the related research done by scholars, this research team also tried to combine burned joss paper ash (BJPA) is similar to that of ground-granulated blast-furnace slag (GGBFS) as a new geopolymer material. Religious beliefs and traditional customs in Taiwan have resulted in the production of a large amount of BJPA without a fixed processing site. Taiwan burns up to 34,920 tons of joss paper annually, which are generally discarded without further processing, producing waste that seriously pollutes the environment. Taiwanese scholars have been studying BJPA as a partial substitute for cement and fine aggregate, and discovered that a substitution ratio of 2.5-10% results in early and late strengths that are 11% higher than those of the control group, indicating that adding BJPA helps increase structural strengths [36]. Regarding the appropriate water-to-gel and substitution ratios, it is feasible to replace a portion of cement and fine aggregate with BJPA. Despite the effectiveness of the BJPA in replacing cement, the problem of the vast amount of ash produced annually remains unresolved. The effective recycling of BJPA not only reduces processing costs, but also turns it into a green recycled material that reduces environmental pollution. No research has yet been conducted on the application of BJPA in geopolymers. Based on the concepts of energy saving, carbon reduction and resource sustainability, this study aims to use BJPA for reuse in GGBFS-based geopolymers.