The object of this study is to investigate the thermal properties of fly ashes from the last, farthest dedusting zone in terms of their use as ceramic masses additives. Siliceous fly ash is valuable additive to ceramic mass, which not only reduces its plasticity, but also actively affects sintering process and shapes the properties of the final material. The finest fly ash fractions are potentially useful flux materials in ceramics; however, a significant limitation in their use is due to thermal expansion/bloating occurring during high-temperature sintering. The bloating mechanism of fly ashes was investigated in relationship to their chemical composition with the use of DTA/TG/EGA analysis as well as high-temperature microscope. Chemical and phase compositions were studied by X-ray fluorescence and X-ray diffraction. Based on the results obtained, it can be concluded. The results indicate that bloating mechanism is caused by the co-occurrence of two phenomena accompanying sintering: appearance of high amount of liquid phase and simultaneous gas release from sintered material. The dominant mechanism is the simultaneous release of sulfur (IV) oxide and oxygen as a result of the redox reaction of removing SO₃ from the vitreous phase.

E3S Web of Conferences, open access proceedings in environment, energy and earth sciences

Porous materials are subjected to the corrosive effects of soluble salts. This corrosion, typically known as efflorescence, is primarily superficial. However, internal corrosion within the material is also frequently observed. This article presents a simulation of volumetric damage in sintered porous ceramic materials (made of clay (75 vol.%), quartz sand (10 vol.%), and sawdust (15 vol.%), fired at 950 °C), caused by the crystallization of double salts, specifically ploweite (6Na₂SO₄·7MgSO₄·15H₂O) and/or glauberite (CaSO₄·Na₂SO₄). The exact mechanism responsible for the formation and interaction of these salts has yet to be fully comprehended. It is established that this mechanism occurs in ceramic materials containing calcium compounds and in mixtures of Na₂SO₄ and MgSO₄ salts. Dissolved Na₂SO₄ acts as a substrate for the formation of glauberite, while dissolved MgSO₄ participates in intermediate reactions (which are necessary for the creation of glauberite).

A large group of industrial and municipal waste are glassy in nature. One of the main directions of their use is thermal treatment, which aims to melt them (solid waste) or sinter (powdered waste). Fine grained glass cullet as well as silica fly ash was the subject of our research. During heating of glassy powders, high sintering dynamics is observed along with the accompanying glass devitrification process. Our objective in this research was to partially or entirely decouple the simultaneous occurrence of glass crystallization reaction and the sintering process during the heat treatment of glassy wastes. We divided an experiment onto two parts, first we compared the effects of thermal treatment on glass in the form of: pressed powder and a bulk glass. In the second experiment the influence of the powder sample density on the progress of glass crystallization was analysed. Results of our study indicate that physical sintering of glassy powders can lower the devitrification temperature of this material. However, physical sintering is accompanied by shrinkage, which when high density is achieved can limit the expansive growth process of grains formed during devitrification. Graphical abstract

The main challenge for the European cement industry in the last decade is so-called decarbonisation, i.e. reducing CO2 emissions throughout the entire production cycle. In the case of the cement industry, this task is difficult because most CO2 emissions come from the thermal dissociation of calcite present in raw materials for the production of Portland clinker. The main way to reduce CO2 emissions from this source is to use calcium oxide sources in non-carbonate form. In practice, however, the availability of such raw materials in Europe is very limited, and their import from other continents is not only unprofitable, but also environmentally unfriendly due to emissions generated during transport. However, there are examples of the use of waste raw materials containing calcium oxide in the Portland clinker production. These include, among others, granulated blast furnace slag, converter slag, carbide lime, lime ash, as well as glass cullet which is the subject of analyses. The aim of the research is to analyse the burnability of clinkers with the addition of various glass wastes. The glass wastes selected were those that could not be reused in glass production due to contamination and fine-grained form. The use of glass cullet was quantitatively limited due to the high Na2O content [13 % –15 %]. Glass waste introduced into the raw material batch is mainly a source of SiO2 [67 % –- 69 %] and to a lesser extent CaO [9.0 % - 12.4 %]. The introduction of even small amounts of cullet increases the demand for high-lime raw material and also raw materials that are sources of Al2O3 and Fe2O3. Although glass waste introduces CaO in a non-carbonate form, the above changes in the raw material feed combined with the presence of carbonates in raw materials other than calcite [dolomite, siderite] mean that the addition of glass cullet does not necessarily reduce CO2 emissions from raw materials. The positive effect of the addition of glass waste on the burnability of raw material batches is noticeable at temperatures of 1200 °C – 1250 °C. It is probably related to the high Na2O content in the glassy waste and its amorphous form.

The article presents the results of research on cements containing calcined illite clay with relatively low clay minerals (20-23 wt.%) and a high limestone content used as a substitute for Portland cement (CEM I 42.5R) in an amount of 10% to 30% by weight of the binder. The results were compared with OPC and cements containing 30 wt.% siliceous fly ash or granulated blast furnace slag, or mixtures of these components with calcined illite clay in weight ratios of 1:2 or 2:1. The results showed a relatively high reactivity of the carbonate component with the calcined clay minerals. This caused a shorter induction time than cements containing a comparable amount of siliceous fly ash or granulated blast furnace slag and higher strength characteristics in the first days of hydration. The high reactivity in the tested system results in higher strengths up to day 7 compared to slag-containing cements and up to day 28 compared to siliceous fly ash. DTA/TG analysis showed the consumption of Ca(OH)2, calcium carbonate, and the formation of carboaluminates with increased calcined clay content.