Multi-response Optimization of Mechanical Properties of Alkali-Activated Mortars

Nowadays, due to energy consumption and adverse environmental effects, it is becoming increasingly important to use different materials to reduce cement consumption. For this purpose, using alkali-activated materials (AAM) in the construction industry is becoming widespread. Due to the complex structure of AAMs, it is necessary to determine the optimum values of the variables that affect the desired mechanical properties. Therefore, multi-response optimization of the mechanical properties of alkali-activated mortars was performed in the study. Cementitious materials (fly ash and blast furnace slag), activators (sodium hydroxide (NaOH) and sodium metasilicate (Na2SiO3)), standard sand, and distilled water were used for the production of mortars. The effect levels of the effect variables (Na2SiO3 solution/NaOH solution ratio—by weight, A; total alkali solution/binder ratio—by weight, B; molarity of NaOH solution, C; Na2SiO3 solution water/Na2SiO3 solution ratio—by weight, D) on the response variables (ultrasonic pulse velocity, UPV; flexural strength, ff; Compressive strength, fc) were determined by analysis of variance (ANOVA) using a rotatable central composite design. The B and D terms have a significant effect on UPV and fc. The run point, which provides optimum mechanical properties at the selected variation ranges, was obtained using desirability functions (A: 1.88; B: 0.4; C: 11.5; D: 60; UPV: 4.18; ff: 6.6; fc: 45.3). The combined desirability value of the optimum run point is 0.81. This value shows that the desired target values are achieved due to multi-response optimization of the mechanical properties.