Development of one-part new type geopolymer binder from boron mine wastes

Our country has the largest part of boron reserves of all over the World (>%70). Hence, boron is a stragetic mine for Turkey.Waste materials containing a sum of boron (15-20%) occur during boron benefication with different mining procedures. Boron mine tailings are not been evaluated completely in any sector and a large portion of these waste materials are stored in tailing dams. The evaluation of waste materials is of great importance in terms of producing the sustainable construction materials. In the scope of this thesis, the use of of boron waste as a raw material, discarded from Boron facilities located at the regions of Emet-Kütahya, Kırka- Eskişehir ve Bigadiç- Balıkesir, was investigated to produce one-part geopolymer binder via alkali fusion method. The experimental studies have performed in three stages. At the first stage, the optimum calcination temperature and duration, the type and ratios of activator were determined in the production of one-part geopolymer binder. In this stage, two different activators, which were sodium hydroxide and sodium carbonate were used. The powder materials were mixed with sodium hydroxide (2%, 4%, 6%, 8% and 10%) sodium carbonate (5%, 10%, 15% and 20%) at several ratios. After that, the mixtures containing activator were calcined at 600 °C, 650 °C and 700 °C of calcination temperatures during1h, 2h, 3h, 4h, 5h and 6h. At the second stage, the optimum curing temperature and duration were determined on the mortar mixture, which was selected at the end of test results of first stage. The prepared mortar mixtures were cured at 60 °C, 80 °C and 100 °C during 12h, 24h and 36h. The compressive strength values of the mortar specimens were obtained after the end of curing process. At the third stage, the mortar specimens were produced using the optimum parameters, which were obtained at the end of both first and second stage. The experiments of the fresh state (setting time and workability), mechanical (compressive and flexural strengths), permability (capillary and total water absorption), drying shrinkage, resistance to water, resistance to high-temperatures were conducted on the mortar mixtures. Furthermore, microstructure investigations were performed on the selected paste mixtures. In addition to high temperature curing process, the ambient temperature curing process was carried out on some mortar specimens produced with one-part geopolymer binder. According to obtained results, the best boron waste in the production of one-part geopolymer binder was the waste which is located Kırka-Eskisehir. The boron waste should be calcined at minimum 650 °C during 3h to produce one-part geopolymer binder. Furthermore, the curing temperature and duration should be at least 100 °C and 12 h to obtain reasonable level compressive strength from the mortar mixtures prepared with 100% boron waste. In case of implementing ambient temperature curing, the blast furnace slag should be partly replaced with boron waste. In case of heat curing, the maximum compressive strength value (24.2 MPa) was obtained from the mortar specimens with sodium hydroxide activator containing 4% Na2O. Among the mortar specimens cured at ambient temperature, the maximum compressive strength value (18.4 MPa) was obtained from the mortar specimens containing 50% of boron waste, which was activated with sodium hydroxide containing 12% Na2O at 7 days. Moreover, the compressive strength values of this mortar specimens at the age of 28 and 56 days were 28.9 MPa and 35.3 MPa, respectively. As a result of microstructure analyses, the main reaction product of one-part geopolymer paste specimens has been riversideite phase, which has the binding property. In other words, this phase is C-S-H gel which is a member of tobermorite gel. C-S-H gel is responsible for the improvement of the compressive strength of the mortar specimens. Finally, the C-(A)-S-H gel was detected to form in the microstructure of mortar specimens cured at ambient temperature.