| Abstract [eng] |
This work investigates the possibility to use technogenic wastes generated in Lithuania (silica-gel with fluorine ions and granite powder) in the synthesis of belite sulfoaluminate ferrite clinker, also hydration and main properties of the obtained cement. In order to synthesize clinker, two composition of initial mixtures were used: the first with 3.81% of silica-gel (BSFC-1) and the second without silica-gel (BSFC-2). Clinker synthesis was performed in a high-temperature furnace in the temperature range of 1000–1250 °C. It was determined that the temperature range of 1100–1150 °C is optimal for the synthesis of belite sulfoaluminate ferrite clinker because raw materials fully reacted and only hydraulically active compounds were formed. It was investigated that that the composition of the initial mixture does not affect the amount of the main synthesis product – belite (~53%) however, it affects the stability and quantity of other synthesis products. It has been observed that the initial composition of BSFC and content of gypsum additive changes the mechanism of belite sulfoaluminate ferrite cement hydration. In the mixtures without gypsum additive, the hydration reactions ends after 20 minutes, meanwhile using the optimal amount of gypsum additive (7.5% for the BSFC-1 sample, 12.5% for the BSFC-2 sample) the main hydration reaction starts after 2–3 hours which is a sufficient time period to prepare cement products. In this work the influence of hardening conditions on BSFC cement mechanical and physico-chemical properties was determined. The curing in an aqueous environment was performed according to the modified standard LST EN 196-1 and LST EN 197-1 methodology when the formed standard prisms were kept in molds above water for 24 hours and then (after disassembly of the molds) the samples were transferred to water at 201 °C temperature where samples were maintained for 3, 7, 14, 28, 56, and 90 days. It was obtained that after 3 days of hydration the compressive strength of the BSFC-1 and BSFC-2 samples were equal to 4.25 MPa and 6.61 MPa, respectively. By extending hydration to 90 days, the mentioned values increased to ~10.35 MPa and ~10.24 MPa, respectively. In addition, the curing of belite sulfoaluminate ferrite mortar in the saturated water vapor at 90 °C, 100 °C, 125 °C, 150 °C, 175 °C and 200 °C temperatures was investigated. The rate of temperature rise was 25 °C per hour, while curing duration was 6, 12, 24 and 48 hours. It was determined that the optimal curing conditions are 24 h and 200 °C temperature, because the concrete products reached the highest value of compressive strength (20,07 MPa) and crystallization of 11Å-tobermorite proceeded in the cement stone. |
