Testing of Geopolymer Raw Materials: Validation of Methods and Practical Aspects

The most used raw materials to produce geopolymers are metakaolin, fly ash, mine tailings, and granulated blast furnace slag. The geochemical composition of the starting materials is decisive for the structure and physical properties of the newly synthesized geopolymer. The present research is aimed at validating methods to determine pH, electrical conductivity of initial raw materials for the preparation of geopolymers. Methods trueness and precision were estimated by bias, z-score and repeatability determination. The results from certified reference material clay soil for pH and EC CRM498-100G, Lot LRAC5544 tests showed that the bias was 0.18% for pH and –1.7% for EC. The repeatability was 0.18% and 2.38% for pH and EC, respectively. The z-score was below 2 and the analytical behavior of both studied methods was evaluated as satisfactory. The validated procedures were applied to mine tailings and coal combustion by-products from four sources from Bulgaria, Romania, and Portugal. The aqueous slurry of industrial wastes was with pH 6-12, all studied fly ashes contained high concentration of components ionized in water solution. The results showed that the studied raw materials could be used as precursors for geopolymer.