International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Geopolymers based on natural zeolite clinoptilolite and addition of up to 50% metakaolin were synthesized using binary sodium/potassium alkali activator. The influence of metakaolin addition was evaluated on apparent density, water absorption, relative mass loss after watering and microstructure (XRD) of the prepared geopolymers. The addition of metakaolin greatly influenced the physical and mechanical properties of the obtained geopolymers. Minimal/optimal metakaolin addition was estimated to 30% in the respect of sufficient strength (11 MPa) and the high price of metakaolin. The resulted geopolymer based on natural zeolite and metakaolin (30%) contained residual unreacted clinoptilolite which could be beneficial for properties of future geopolymer products. Potential applications of obtained geopolymer-clinoptilolite agglomerates are: waste or radioactive water decontamination, passive cooling systems, plasters in residential buildings, etc.

Geopolymer based on iron-silicate fines (fayalite slag) were synthesized in alkaline and acidic media using activation solution
comprised of respectively alkali silicate and phosphoric acid solutions. The raw material consists of fayalite, magnetite and pyroxene which could be a conglomerate in some particles. The alkali activation occurs very slow at room temperature, while acid activation take place very rapid. The acid activated geopolymer binder phase include cracks probably formed by thermal gradient because of the rapid exothermal reaction. The morphology of the alkali activated geopolymers were presented by porous structure.

The geopolymers are novel class of inorganic polymer materials consist of chains, sheets or networks made of covalently bonded mineral molecules. The main precursors of the geopolymers are reactive alumosilicate material and hardener solution. Various suitable raw materials are located in Bulgaria. The present paper shows successful examples of geopolymers based on Bulgarian raw materials – fly ash, metakaolin, natural zeolite and iron-rich waste from copper industry. The properties and structure of the prepared geopolymers greatly depend on the composition and type of the raw material, as well as concentration and type of the activator solution. The results show the potential of geopolymers based on Bulgarian raw materials as building materials.