Yakymenko O. Raising efficiency of the ferroconcrete casings of the tunnel erections

The work is dedicated to the revelation of the specific features of the influence of fire temperature regimes as well as thermal and physical characteristics of some fire retardant coatings upon their minimum thickness values to ensure the standardized fire resistance rating of the ferroconcrete casings of the tunnel erections. There has been substantiated for the constructions mentioned above such the criterion of the limiting state for fire resistance as reaching a critical temperature value of 380 ?C at the heated side of the concrete surface of the construction at that crumbling-type concrete destruction starts. Relation of the minimum necessary thickness of a fire retardant coating of the ferroconcrete casings of the tunnel erections upon values of its thermal and physical properties has been determined. Influence of a number of fire temperature regimes upon fire retardant capability of some coatings has been revealed. A method for the estimation of the fire retardant capability of some coatings of the ferroconcrete casings of the tunnel erections based on the regulations of the experimental and calculation method has been developed. Essence of this method lies in the experimental determination of the temperature at the concrete surface of the specimens of some constructions being heated under laboratory conditions applying standard temperature regime, determination of thermal and physical characteristics of the fire retardant coating by way of the solution of the heat conduction inverse problem, and calculation of the minimum thickness of the coating for the standardized fire resistance ratings by way of the solution of the heat conduction direct problem. Using this method the necessary minimum thickness values for two types of fire retardant coatings ("Neospray" plastering material and "Promatect L500" slabby one) were determined in order to ensure standardized fire resistance ratings of the ferroconcrete casings (30, 45, 60, 90, and 120 min.) under various fire temperature regimes. Recommendations for the improvement of the fire resistance of the ferroconcrete casings of the tunnel erections have been developed.