SODIUM-SILICATE GEOPOLYMERS BASED ON NATURAL ZEOLITE - CLINOPTILOLITE

The influence of different modulus (MR=SiO2/Na2O=2 divided by 3) sodium silicate solutions was examined on geopolymer pastes based on natural zeolite clinoptilolite from Beli Plast deposit, Bulgaria. Physical and mechanical properties of the samples were determined and the phase composition and structure were investigated using XRD and FTIR. The results showed that geopolymers based on natural zeolite possess slow rate of strength gain at room temperature. With increasing the modulus (MR) the geopolymer samples possess higher rate of strength gain, but lower final strength. Due to the crystallinity of clinoptilolite the alkali concentration of the used sodium silicate reagent solutions were not sufficient to dissolve the raw material and induce high degree of polycondensation. Mixing sodium silicate with MR above 2 with the zeolite led to formation of geopolymer material containing certain quantity unreacted clinoptilolite, which could preserve the beneficial properties of the clinoptilolite per se.