After fire in buildings investigators start research. The purpose of it is to find the reason of fire, but this thing can be reliably determined only if the fire origin is fixed. The instrumental fire prognosis for wooden structures is currently the most widely applied method in Lithuania. But the analysis of charring of natural wood specimens and the completed tests have revealed some drawbacks of this method, because the method fails to fully estimate the properties of wood and its protection by fireproofing compounds, the impact of the fire load, etc. The obtained test results will help further resolve the problems of reliability of the above-mentioned method.

Abstract. The properties of the hardened concrete depend on the selected raw materials: size and amount of the particles of coarse aggregate, as well as on the ratio of other components. Particular countries use various methodologies for the selection of concrete composition to select the components of the concrete mixture. However, the properties of the concrete, selected by using any methodology for the selection of the concrete composition and hardened by following the defined conditions, must satisfy the values of certain necessary characteristics. The results of the implemented research indicate that the most optimal solution is to use the coarse aggregate of multi-fractional or discontinuous fractional composition. The optimal composition of the concrete must be selected to ensure that the binding material is not overdosed. Yet, all components must be selected in such a way, that the required properties of the final product are retained after concrete mixture hardens. When catalyst waste materials from the reactor of the catalytic cracking (15%) are used for the lightweight concrete, the density of the expanded-clay lightweight concrete investigated and compressive strength increases even for the higher water/cement ratio, more heat is dissipated during the hydration of the cement and this exothermic effect occurs several hours earlier.

This paper presents the research on the structure and compressive stress or compressive strength of mineral wool products. The products of chaotic, directional and combinative fibres structure have been studied visually and microscopically. During mechanical tests it was determined that compressive stress (compressive strength) of the stone wool products is dependent on the direction of the load working to the product major face, test specimen dimensions, force increasing rate, fibres distribution (orientation) and methodical peculiarities.

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