There has been a tendency to design ever slender building construction using high strength concrete in recent years. Application of HSC is also growing in tunnel construction. One of the most important challenges is to control explosive spalling of concrete and the method recommended by Eurocode 2 (EN 1992-1-2:2008/NA:2010P) is addition of polypropylene fibres to the mix. The purpose of the research described in this paper was to evaluate the changes of mechanical properties of HSC exposed to the effect of high temperature. The tests were carried out on three types of high strength concrete: air-entrained concrete, polypropylene fibre-reinforced concrete and reference concrete having constant water/cement ratio. The properties of hardened concrete including compressive strength, tensile splitting strength, flexural strength and E-modulus were studied. The latter tests were carried out on both on concrete cured at 20 °C and concrete subjected to high-temperature conditions at 300 °C, 450 °C and 600 °C. The results enabled us to evaluate the effect of high-temperature conditions on the properties of high-performance concrete and compare the effectiveness of the two methods designed to improve the high-temperature performance of the concrete: addition of polypropylene fibres and entrainment of air.

Due to the thermal modernization process of old residential buildings, there has been a significant increase in the air-tightness of apartments, which may contribute to the deterioration of the safety of users and rescue teams in a fire, for example, the emergence of a very dangerous backdraft phenomenon. The aim of the study was to investigate the impact of air-tightness of premises on selected fire parameters in particular toxic gas concentrations, which is the most common cause of deaths of people due to fires. In the research, an experimental method was used, consisting of the measurement of concentrations of gases such as oxygen, carbon monoxide and dioxide, hydrogen sulfide, propylene, acetylene, hydrogen and nitric oxide, and dioxide, which most often give off during a fire due to modern interior design materials. Two fire tests were carried out, one in a sealed apartment and the other unsealed (one window wing half-open). The concentrations of the previously mentioned gases obtained in both tests are presented and then compared with each other. Based on the analysis, conclusions have been formulated, which suggest that increasing the tightness may increase the toxicity of the fire environment.

A general concept of a hybrid modelling of fire dynamics in the compartments is presented. The hybrid fire model combines the advantages of both zone and field models. The assumptions applying to physical model of fire and its mathematical description are given. Some problems related to application and development as well as verification and validation of the model are discussed. Santrauka Aprašyta gaisro hibridinio modeliavimo bendroji koncepcija. Gaisro hibridinis modelis susieja zonų ir laukų modelių privalumus. Pateiktos fizikiniame modelyje naudojamos prielaidos, aprašyta matematinė modelio dalis. Aptarti kai kurie taikymo ir tobulinimo, kaip ir rezultatų patikrinimo ir patvirtinimo, ypatumai.