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One of the potential raw materials for preparation of geopolymers is the natural zeolite. In the present report, the used natural zeolite (clinoptilolite) is from huge deposit near Beli Plast, Bulgaria. Geopolymer pastes and mortars are prepared by using three different alkaline activators—sodium hydroxide, sodium silicate and sodium carbonate. The hardened geopolymers are tested for determination of mechanical properties by traditional standardized methods. The structure and the composition of the materials are studied by direct physical methods—X-ray diffraction (XRD), thermal analysis (DTA and TGA) and scanning electron microscopy (SEM). The results show variable degree of dissolutions of the raw zeolite material when using different activators and formation of solid geopolymer materials with qualitatively different structure. Despite its relatively low compressive strength, geopolymers based on natural zeolite cured at room temperature and used as coating, show very good adhesion to concrete.
Nikolov et al. (Mon,) studied this question.