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The aim of present article is to describe influence of composition of refractory composites on its response to gradual thermal loading. Attention was focused on the impact of ceramic fibers and application of metakaolin as an aluminous cement supplementary material. Studied aluminate binder system in combination with natural basalt fine aggregates ensures sufficient resistance to high-temperature exposure. Influence of composition changes was evaluated by the results of physical and mechanical testing-compressive and flexural strength, bulk density, and fracture energy were determined on the different levels of temperature loading. Application of ceramic fibers brought expected linear increase of ductility in studied composites. Metakaolin replacement showed the optimal dose to be just about 20% of aluminous cement weight.

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Formulation process of Ultra High Performance Fiber Reinforced Concrete (UHPFRC) is described in this paper. Materials locally available in the European Union were used throughout the optimization process. The mixture was also developed without any special curing, such as elevated temperature, pressure or vapor. The optimization process consisted of two steps. In the first step a cementitious matrix was optimized with respect to its maximal compressive strength, flexural strength and workability. The key element in the optimization process was to achieve maximal particles packing density, to choose efficient enough high-range water reducer (HRWR) and to decrease water binder ratio as much as possible. In the second step of the optimization process short, high tensile strength steel fibers were added into the matrix that showed highest workability and strength. The resulting compressive strength of UHPFRC mixtures exceeded 150 MPa after 28 days, average secant modulus of elasticity was in the range of 55 GPa and direct tensile strength in range of 10 MPa. During the optimization process mixtures with 1, 2 and 3% of fibers by volume were tested. It was found that with respect to acceptable workability and superior mechanical performance the optimal fiber content is between 2 and 3% by volume.

The motivation for utilization of active admixtures in concrete lies primarily in a positive effect on properties of hardened concrete with regard to its durability. Fine parts complement the grain size distribution curve, but also due to subsequent hydration arise phases with better resistance to aggressive substances from surrounding environment. Process of pozzolanic reaction is also associated with a reduction in open capillary porosity, causing a gradual reduction of the permeability of concrete. The paper presents an experimental program focused on the monitoring of evolution of basic and hygric properties of concrete with fine ceramic powder addition.