Effect of thickness of the intumescent alkali aluminosilicate coating on temperature distribution in reinforced concrete

Abstract

The paper presents the results of investigations to determine the optimum thickness of intumescent aluminosilicate coating providing protection of concrete and reinforced concrete structures, in particular tunnels, in case of fire. It is shown that the developed intumescent aluminosilicate coating prevents heating of the surface structures of concrete and metal reinforcement of concrete to the limiting condition, i.e., to temperatures of 653K and 773K. The protective coating on the concrete surface, in thicknesses of 6mm, can prevent concrete and reinforced concrete from brittle fracture and reinforcement from occurrence of plastic deformation for at least 2h. The developed coatings were studied by heating the coated concrete surface using a spot fire (point source fire) for a period of 3h, and temperatures beneath the coating and at a distance of 20mm from the surface (embedded reinforcement) were measured. Measurements of pull-off adhesion of the coating were taken using an adhesion testing equipment before and after exposure of fire. Increasing the thickness of the protective coating reduces heating of the concrete in depth; the average temperature of the heating of the concrete at the depth of the metal reinforcement (20mm) is 414.4K, which is 1.9 times less than the limit of heating temperature of the metal fittings. The increase in thickness of the coating and time of fire exposure will result in even better heat insulating and fireproofing properties. Test results of the developed coating 6mm in thickness suggested concluding that before exposure of fire type, its type of fracture – was А/В (concrete substrate/coating adhesion fracture) and its pull-off strength was 2.15MPa. A mean value of adhesion (pull-off strength) of the developed coatings 12 and 18mm in thickness was 1.55MPa, type of fracture – В (cohesion fracture within the coating). After exposure of fire, not depending upon thickness of the coating, a mean value of adhesion (pull-off strength) was 0.85MPa, type of fracture – В (cohesion fracture within the swollen porous coating).