Application of HPC (High performance concrete) is very popular and modern solution in current architecture. Higher mechanical and durability properties allow using of thin-walled cross-sections bringing savings of materials and internal space of buildings. This paper deals with development of HPC and UHPFRC (Ultra high performance fiber reinforced concrete) mix design and impact of composition to final mechanical properties. Mix design is focused first on the influence of various additives such as fly ash, silica fume and quartz flour and then to different dosage of steel fibers.

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.

Present paper deals with the experimental study of the composition of refractory fiber-reinforced aluminous cement based composites and its response to gradual thermal loading. Basalt fibers were applied in doses of 0.25, 0.5, 1.0, 2.0, and 4.0% in volume. Simultaneously, binder system based on the aluminous cement was modified by fine ground ceramic powder originated from the accurate ceramic blocks production. Ceramic powder was dosed as partial replacement of used cement of 5, 10, 15, 20, and 25%. Influence of composition changes was evaluated by the results of physical and mechanical testing; compressive strength, flexural strength, bulk density, and fracture energy were determined on the different levels of temperature loading. Increased dose of basalt fibers allows reaching expected higher values of fracture energy, but with respect to results of compressive and flexural strength determination as an optimal rate of basalt fibers dose was considered 0.25% in volume. Fine ground ceramic powder application led to extensive increase of residual mechanical parameters just up to replacement of 10%. Higher replacement of aluminous cement reduced final values of bulk density but kept mechanical properties on the level of mixtures without aluminous cement replacement.

This paper summarizes the results of an experimental program aimed at investigating of the mechanical properties of composites based on aluminous cement for high-temperature applications and deal with the influence of high-thermal loading on polycarboxylate superplasticizing (PCSP) additive contained in the composite. The intent of this examination was caused by the suspicion that the action of high-temperatures can lead to burnout of the PCSP additive and thus subsequently affecting the mechanical properties of the final composite. Silica composites based on Portland cement and silica aggregates are not able to resist the effects of high-temperatures [1]. For high-temperature composites was therefore used aluminous cement Secar®71 (Lafarge S.A.) in combination with crushed basalt aggregates of fraction 0/4 and 2/5 mm. The flexural strength was greatly improved thanks combinations of basalt fibers with lengths of 6.35 mm and 12.7 mm. The values ​​of flexural strength and compression strength were investigated on samples dried at temperature 105 °C or loaded for 180 minutes with high-temperature of 600 °C or 1 000 °C.

The main aim of this contribution lies in the description of mechanical properties fiber cement composites after exposure to high temperatures. Destructive and non-destructive methods were used to investigate the influence of heat loading. The effect of refractory binder compared to common Portland cement binder was observed. Widespread non-destructive testing method can describe the changes of mechanical properties due to influence of external load e.g. high temperature at the level of 1000 °C. The tensile strength and compressive strength were investigated on specimens 40 x 40 x 160 mm. Before these destructive tests dynamic modulus of elasticity and tentative compressive strength were provided.

The interaction of ultrahigh-performance concrete (UHPC) and normal-strength concrete (NSC) is one of the main issues for strengthening conventional concrete structures or other applications where NSC and UHPC are interrelated. UHPC stands out for its strength and durability, while NSC is significantly inexpensive and easier to work with. Efficiently designed structures can exploit the advantages of both mixtures. At the interface of these materials in newly designed structures, the formwork can be modified at the interface to give the concrete surface sufficient roughness and thus cohesion as required. This improves both the tensile and shear strength of the contact resulting in the enhanced capacity of the composite structure. In this study, a button foil was inserted into the formwork for the UHPC and then a part of NSC was made. The shear strength of the interface without any stress component in the transverse direction was measured on small-scale samples. It was to justify the possibility of the use of this interface in real constructions such as beams and columns. The main objective of further research is to design a composite beam using a UHPC shell as formwork for NSC and protrusions at the interface. It is expected that the U-shaped shell made of the UHPC could significantly contribute to the load-bearing capacity of the resulting composite NSC–UHPC structure and also to its enhanced durability. In addition, if the NSC is enclosed in a shell of UHPC, it can be made from various secondary materials, therefore it can decrease cement consumption by more than 50%.