| Abstract [eng] |
Cement industry is one of the most energy-intensive industries. Partial cement clinker replacement in the Portland cement with other materials allows not only to reduce the cost of Portland cement, but also to protect the environment by reducing CO2 emissions. Recently, the pozzolanic properties of burned clays intensively have been investigated, because during the combustion process, some of clay minerals (mainly kaolinite) transforms into amorphous state, which is characterized by pozzolanic activity. However, clays of Lithuanian quarries are rich in hydromica and are limited in kaolinite. On the other hand, Lithuania is rich in technogenic wastes. One of them is silica gel, which forms during the production of AlF3 in the factory of JSC “Lifosa“. This waste is stored in the landfills due to the fluoride impurities in it. The synthesis of an active pozzolanic additive from clay and silica gel would allow reduction of environmental pollution and Portland cement cost. In this dissertation, changes of mineralogical composition and pozzolanic activity of selected clays and silica gel during combustion process are presented and the influence of silica gel–clay mixtures composition and their combustion temperature on the pozzolanic activity of combustion products is evaluated. Furthermore, thermodynamic parameters calculations of metal fluoride formation in model system and compositions of the clay–silica gel mixtures, from which active pozzolanic materials are synthesized without emission of fluorides into environment, are provided. Moreover, discussion of the influence of pozzolanic additives on Portland cement hydration process and compressive strength of cement stone is presented. |
