Multivariate analysis of a geopolymeric system containing metakaolin and a-Al2O3

Geopolymer materials are a promising and eco-friendly alternative to Portland cement. This work investigates the combined effect of a-alumina (a-Al2O3) content, temperature, and curing conditions on the mechanical properties of metakaolin-based geopolymers containing a-Al2O3. The influence of a-Al2O3 content and curing temperature (T-c) were evaluated using a central composite design. The geopolymers were developed from metakaolin/a-Al2O3 mixtures activated with a NaOH solution, uniaxially pressed (33 MPa/30 s), and cured at the experimental design temperatures under different conditions: i) curing for 24 h; ii) pre-curing at room temperature for 24 h and curing for 24 h and iii) pre-curing for 24 h and curing for 48 h. Statistical analyzes were performed to evaluate the variables' significance (a-Al2O3 content and T-c) and their interactions. Response surfaces modeling and mathematical models were described to predict the flexural strength values as a function of each curing condition. The results showed that temperature and curing time has an essential role in the flexural strength (s(f)), with the temperature being a significant factor in all experimental conditions evaluated. Inserting a pre-curing step at room temperature for 24 h favored the increase in sf values. Furthermore, regardless of the % a-Al2O3, the sf for samples with pre-curing did not vary significantly with the curing time.

Automated summary

This study investigates the effect of a-Al2O3 content, temperature, and curing conditions on the mechanical properties of metakaolin-based geopolymers containing a-Al2O3. The results show that temperature and curing time play a crucial role in the flexural strength (sf), with temperature being a significant factor in all experimental conditions. Inserting a pre-curing step at room temperature for 24 hours favored an increase in sf values. Regardless of the % a-Al2O3, the sf for samples with pre-curing did not vary significantly with the curing time.