At the present time in Russia the construction of buildings and structures of concrete and reinforced concrete structures is developed. Different cement composites, structural elements, the building are shown the behavior differently in terms of exposure of fire and high temperatures. However, there is hardly any method of complex analysis of the behavior of materials at elevated temperatures in building structures, and the existing methodologies to determine the fire resistance do not provide a full assessment of fire hazard of building structures and construction materials from which they are made. Along side with this process new types of materials that can effectively protect the building structure from thermal effects are developed. So the Department of Fire Prevention of Ivanovo Fire and Rescue Academy of the State Fire Service of Emercom of Russia together with the Department of Building Materials, Special Technology and Technological Complexes of Ivanovo State Polytechnic University developed mortar compositions with increased thermal stability, which contain a supplement of liquid glass and fiberglass. Research and calculations performed with the participation of these compositions showed that the method for determining the fire resistance of concrete structures can be used to characterize the impact of different components of the raw mix cement composite thermal insulation properties of the protective solution and fire resistance of reinforced concrete hollow core slabs. The research was conducted on the compositions of heat-resistant plaster. Their average density, thermal conductivity was determined. To determine the fire resistance of building structures with using the developed mortars such a thermal characteristic as thermal conductivity was determined. The data shows that heavy concrete has a higher fire resistance than conventional mixes the solution at the same thickness. The addition of mineral fibers increases the fire retardant properties of the solution. For example, adding 3 % fibers by weight of the solids increases its fire-resistance properties 1.4 times. For example, the fire resistance of the construction in comparison with a layer of heavy concrete in the application layer of a solution containing 3 % of fibers increases by 8 %. Thus, researches and calculations have shown that the method for determining the fire resistance of concrete structures can be used to characterize the impact of different components of the raw mix cement on the thermal insulation of the composite material properties and fire resistance of building structures.