The Use of Heat-Resistant Concrete Made with Ceramic Sanitary Ware Waste for a Thermal Energy Storage  
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33 Faculty of Civil Engineering and Architecture, Lublin University of Technology, 40 Nadbystrzycka Str., 20-618 Lublin, Poland 333 Faculty of Civil Engineering and Architecture, Lublin University of Technology, 40 Nadbystrzycka Str., 20-618 Lublin, Poland 33 Faculty of Civil Engineering and Architecture, Lublin University of Technology, 40 Nadbystrzycka Str. considered as HPCs. The properties listed are responsible for faster production of concrete, shortening of curing time, construction cost reduction, early termination of the project, maintenance cost reduction, and longer building service life. Green concretes promote sustainable and innovative use of waste materials and unconventional alternative materials [7; 8]. One of these materials is a recycled aggregate based on ceramic sanitary wastes, which are often called white ceramics. In the research conducted by [9] three types of coarse ceramic aggregate were used: crushed floor and wall tiles, as well as sanitary ceramics. The aggregate was introduced into the mix in a proportion of 20-100%. The results of the research show that it is possible to completely replace the coarse aggregate with the recycled ceramic aggregate. In other studies [10], concrete was tested, which was made solely of the ceramic aggregate derived from wall tiles. Cylindrical samples 100 mm in diameter, and 150 mm cubic-shape specimens were formed, and then they were stored in accordance with the standard requirements. The concrete's compressive strengths after 3, 7, 14, and 28 days of maturing were determined. The results showed that the strength of the ceramic concrete increased with age considerably more than for concrete made of the natural aggregates. Additionally, in [11] it was shown that by replacing 20-25% of the gravel aggregate with the crushed sanitary ceramics, the concrete's strength can be increased with respect to the traditional concrete. In addition to the strength tests, other features of the ceramic concrete were also investigated, e.g., the depth of water penetration. The results showed no difference in relation to the conventional concrete. Studies [12] confirm that the use of the ceramic coarse aggregate in an amount of 30% improves the physical and mechanical properties of the concrete. The results of other studies [12; 13; 14; 15; 16; 17; 18] also confirm the usefulness of the ceramics as the recycled aggregate to concrete. The authors defined guidelines for the design of the non-structural and the structural concretes of a high strength. One of the directions is the production of the refractory and the heat-resistant concretes obtained on the basis of the sanitary ceramic waste material. Attempts were also made to use a ceramic powder as a cement additive. In studies [19], the cement was replaced in amounts of 0%, 5%, 10%, and 20% of the ceramic powder. Despite maintaining the mixture's physical parameters at higher amounts of the ceramic powder, a small decrease in strength of the concrete was observed. The optimum, from the point of view of the mixture's workability and the concrete's strength, was an addition in amounts not exceeding 15%. Similar studies were conducted [20; 21; 22], in which 10-40% of ceramic powder as a substitute for cement was used. It has been shown that such concrete has high strength and durability. At the same time, the powder did not cause any negative effects on the cement hydration process. Additionally, the pozzolanic activity of the mixtures with the ceramic powder was determined. Mortar samples were made in which 25% of the cement was replaced with ceramic powder. A comparison was performed only on samples containing the cement. The pozzolanic activity index tested for mortars after 28 days was 71%, and after 90 days was 74.5%. These values were lower than the standard requirements for fly ash (75% and 85%, respectively), thus, the pozzolanic activity of the ceramic powder was low.