| Abstract [eng] |
In this master's thesis, the use of modified phosphogypsum in binding systems is analyzed through experimental research. Phosphogypsum, as a waste product of AB "LIFOSA" extractive phosphoric acid production, was taken from the waste disposal conveyor, dried and prepared for testing. Its chemical and mineral composition and microstructure were analyzed. The aim of the research work is to chemically modify phosphogypsum into calcium hydroxide and sodium sulfate solution and use the obtained products in binding systems. The final thesis contained an analysis of the literature, a discussion research on the formation of phosphogypsum, the processing of phosphogypsum, the removal of various impurities, and a suggestion of possible ways in which phosphogypsum could be used in the field of building materials. The research methodology and the materials used in the study were also examined. The whole work consists of three main sections. The first is the optimization of the conditions for the conversion of phosphogypsum to Ca(OH)2 and Na2SO4, in which experimental studies have been carried out on the conversion of phosphogypsum to sodium sulfate and calcium hydroxide. After the conversion, the optimal reaction time and concentration were found. The following section is about the dependence of the properties of construction gypsum samples on the amount of sodium sulfate additive. For this experiment, specimens were formed from construction gypsum and water, sodium sulfate was used as an additive from 0 % to 8 % of the gypsum content. The highest strength of the samples was obtained using 1.2 % additive. Based on SEM studies, it was found that sodium sulfate accelerated hydration and led to the formation of more short, needle – like, interconnected crystals, which gave the gypsum greater mechanical strength. As a final investigation, ordinary portland cement mixtures with Ca(OH)2 were examined. The cement used is ordinary portland cement CEM I 52.5 R, which was partly replaced with calcium hydroxide in the mixture. 2x2x2 specimens were formed, and their compressive strength was determined. The results showed that the strongest samples were obtained with 1 – 3 % calcium hydroxide addition. 68.6 and 69.8 MPa, respectively, when the compressive strength of the control specimen reached 64.8 MPa. A summary of the thesis is given at the end of the paper in the form of conclusions. |
