Optimization of Synthetic Fiber–Reinforced Calcined Bentonite–Based Recycled Aggregate Geopolymer Composites Based on Multicriteria Decision Support Method

The study evaluated the mechanical and durability properties of synthetic fiber–reinforced, metabentonite (MB)–based geopolymer composites (GCs) using 50×50×50-mm cubes for compressive strength and 40×40×160-mm prisms for flexural strength, according to standards for density and void analysis, direct tensile strength, and splitting tensile strength. Durability assessments included abrasion resistance and high-temperature effects, with the latter potentially adhering to standards for fire resistance tests of construction materials. First, a preliminary study was adopted on the calcination of bentonite, which was carried out at 900°C. GCs were prepared in various MB/ground granulated blast furnace slag (GBFS) ratios (25%, 50%, 75%, and 100%) with molar concentrations (8M, 10M, 12M, and 14M) and 2:1 Na2SiO3/NaOH. Synthetic fiber reinforcement such as polypropylene fiber (PPF) polyamide fiber (PAF), and basalt fiber (BF) with 0.5%, 1%, 1.5%, and 2% consumption ratios were employed for the mixtures of GCs. This comprehensive study followed a series of steps. The first step depended on determining the mechanical behavior. The second step included the durability behavior of the best GCs for each fiber type inclusion. The best solution chosen/mixture optimization of GCs step depended on a multicriteria decision-making method and a capable method (TOPSIS—Technique for Order of Preference by Similarity to Ideal Solution) to evaluate the results. Accordingly, the best GCs were obtained, and the durability index of the best GC was determined. The GCs were subjected to high temperatures of 200°C, 400°C, 600°C, and 800°C, and the results showed that optimal GCs based on TOPSIS–multicriteria decision support method have 1% PPF, 0.5% PAF, and 0.5% BF fiber content. The BF-containing series showed the best performance among the fiber types. The offered GCs were the possible net-zero/low-carbon materials for future cities.