Orthogonal analysis and mechanism of compressive strength and microstructure of the metakaolin-fly ash geopolymer

Abstract

It is essential to give easier preparation and maintenance methods for geopolymers to facilitate practical application of metakaolin-fly ash based geopolymers (MK-FA geopolymers) in the engineering field. In this article, 16 sets of samples were prepared by orthogonal experiments design (OED) to quantify the order of contribution of three hypothetical influence factors in the growth of compressive strength. Test results revealed that the promotion of the calcium phase was significant. The calcium phase and fly ash acted synergistically during the early stage of strength development, with the former accelerating the hydration process of the precursor materials and the latter providing additional silicon and aluminum phases, which facilitated the formation of the polymeric skeleton and the densification of the matrix. In the later stages of the experiment, the promotion of gel particle formation by calcium effectively mitigated the disadvantage of reduced average reactivity due to the incomplete hydration of fly ash. Moreover, the highest compressive strength was obtained for the MK-FA geopolymer prepared according to the theoretical optimum ratio derived from the orthogonal analysis, which demonstrated the correctness and feasibility of the OED.