Application of DOE method in evaluating for split tensile strength of slag-based boroaluminosilicate geopolymers reinforced with steel fibers

In this research study, the split tensile strength of the steel fibers-reinforced boroaluminosilicate geopolymers was evaluated. The design of experiments was carried out using the Taguchi method. The slag used in this work was obtained from the Rockwool furnace slag. A mixture of anhydrous borax (as an alternative to the silicate composition) and NaOH was used as the alkaline activator. The effect of the amount of flat-end steel fibers (1, 3, 5, and 7 wt. %) on the strength of the material was assessed. Four effective factors, including the curing time of the boroaluminosilicate geopolymer, weight percentage of the fibers, weight ratio of the anhydrous borax to NaOH solution, and weight ratio of the alkaline activator (NaOH + anhydrous borax) to the slag, were designed each at four levels. In total, 16 experiments were performed based on the L-9 array. Based on the ANOVA analysis results, the optimum parameters were the curing time of 14 days, 7 wt. % of steel fiber, the weight ratio of the alkaline activator to the slag of 0.65, and the weight ratio of anhydrous borax to NaOH solution of 0.5; and the highest split tensile strength was found to be 10.08 +/- 0.86 MPa. Also, the specimen prepared using the optimum parameters (with no fiber addition) demonstrated a split tensile strength of 8.10 +/- 0.95 MPa. In addition, the Taguchi experimental design method was found to be an appropriate technique to study the strength of the boroaluminosilicate geopolymers reinforced with the steel fibers.