Optimization of Alkali-Activated Concrete Dosage Based on Metakaolin from the Brazilian Northeast

Alkali-activated structural concretes that are both pumpable and machinable were synthesized utilizing a low-reactivity metakaolin characterized by elevated levels of quartz and iron. The investigation into the effects and interactions of alkaline concentration (NaOH—8, 10, 12, 14, and 16 M) and the ratio of alkaline reagents (Na2SiO3/NaOH—1.0, 1.5, 2.0, 2.5, and 3.0) on the material properties was conducted employing a 2k full factorial design. An increase in alkaline concentration (NaOH), when coupled with a decrease in the ratio of alkaline reagents (Na2SiO3/NaOH), expedited both the initial and final setting times of the mixtures. Elevated alkaline solution concentrations led to a diminished slump, swifter hardening, and enhanced mechanical strength; however, surpassing the threshold of 14 M for the same Na2SiO3/NaOH ratio resulted in a 12.4% decline in compressive strength at 28 days. The factorial design facilitated the identification of the optimal dosage for the material’s production, revealing that an alkaline concentration (NaOH) of 10 M and a Na2SiO3/NaOH ratio of 2.5 are requisite. The evaluation of various potential combinations enabled the attainment of a material possessing properties that are conducive to structural applications.