The use of cement in construction causes large amounts of CO2 emissions into the atmosphere. Moreover, the use of large amounts of natural coarse aggregate causes environmental damage, and the availability of such natural aggregate is also depleting. The present experimental study explores and optimizes the impact of various parameters on the fresh, mechanical, and durability properties of recycled waste concrete coarse aggregate (RWCA)-based geopolymer concrete (GPC) in combination with ground-granulated blast furnace slag (GGBFS) and fly ash (FA) using the Taguchi-Grey Relational Analysis Method (TGRAM). The coarse aggregates in GPC were fully replaced with RWCA produced by crushing waste concrete. The effects of FA inclusion (%), Na2SiO3/NaOH ratio (SS/SH), molarity of NaOH (SH), dosages of superplasticizer (%), and alkaline solution to binder (Al/Bi) ratio are investigated under ambient curing conditions. The obtained maximum compressive strength and split tensile strength along with minimum water absorption of GPC at 28 days were 67.90 MPa, 3.85 MPa and 2.92 % respectively. The microstructural studies of GPC having low, high, and optimal strength are carried out using XRD, FE-SEM, and EDAX analysis. These studies confirmed the presence of calcium-based hydration products such as CSH and N(C)ASH, which makes the matrix of optimized GPC more compact.