In order to reduce the degree of efflorescence in alkali-activated metakaolin geopolymers, a modified 5A zeolite with cation-exchange properties was used to reduce the content of free alkali metal cations in the geopolymer. This work aims to investigate the effect of different dosages of modified 5A zeolite on the microstructure and properties of geopolymer by using compressive strength testing, pore structure analysis (BET), and SEM-EDS. The cation content in the leachate was evaluated using inductively coupled plasma atomic emission spectrometry (ICP-OES). The efflorescence area of the geopolymer was calculated using Image Pro Plus (IPP) software to evaluate the effect of modified 5A zeolite on the degree of efflorescence of the geopolymer and to reveal the effect of modified 5A zeolite on the migration patterns of Na+ and Ca2+ in the geopolymer. The results showed that modified 5A zeolite with a 4 wt.% content could optimize the pore structure and enhance the mechanical properties of MK geopolymer through internal curing and micro-aggregate effects, which could also exchange cations with the pore solution to form (N, C)-A-S-H gels. The Na+ leaching was reduced by 19.4%, and the efflorescence area of the MK geopolymer was reduced by 57.3%.
Keywords: 5A zeolite; cation exchange; efflorescence resistance; metakaolin.