Box-Behnken design based optimization and characterization of new eco-friendly building materials based on slag activated by diatomaceous earth

Abstract

Blast-furnace slag-based geopolymers activated by gels siliceous rock (diatomaceous earth) were synthesized at room temperature. Using a Box Behnken plan and surface response design approach (RSM), the diatomaceous earth content, NaOH molarity, and liquid/solid ratio were used as factors to optimize and evaluate compressive strength, bulk density, porosity, and water absorption. The analysis of variance “ANOVA” revealed that the modelling factor ensembles were significant. Therefore, the high values of coefficient of determination adjusted “R2Adj” (R2Adj-Cs = 95.42%, R2Adj-BD = 92.36%, R2Adj-P = 98.76%, R2Adj-WA = 98.24%), confirm the established models' adequacy. The RSM demonstrated that at a liquid/solid ratio of 0.59, a NaOH molarity of 7.5 mol/l, and a diatomaceous earth percentage of 9.5%, a geopolymer with high physico-mechanical properties could be produced (compressive strength = 42 MPa, bulk density = 1.67 g/cm3, porosity = 18.98%, and water absorption = 11.27%). The optimal geopolymer's microstructural analysis revealed that geopolymer synthesis under optimal conditions supported the formation of a substantial percentage of geopolymerization products, and hence the production of high-performance alkali-activated materials.