The paper presents a description and results of a study focused on the applicability of the sclerometric method to the preliminary assessment of concrete quality in structures after fire. Due to the high thermal inertia, concrete has non-uniform properties in the heated element cross-section. The greatest reduction of concrete compressive strength occurs on the heated surface. When assessing a structure after a fire, it is particularly important to determine the thickness of the damaged external concrete layer. Reinforced concrete beams exposed to high temperature on one side (a one-way heat transfer in the cross-section) for 0 (unheated element), 60, 120, 180 and 240 minutes were examined. A significant decrease of the rebound number on the elements heated surface was observed, depending on the heating duration. The obtained values of the relative rebound number reduction were comparable to the values of relative compressive strength decrease (determined on the basis of temperature) of concrete situated 15 mm from the heated surface.
The paper presents the test description and results of thermal bowing of RC beams exposed to non-uniform heating at high temperature. Bending of a non-uniformly heated element is caused by free thermal elongation of the material it is made of. The higher the temperature gradient, the greater the bending. In the case when an element is exposed to load and high temperature simultaneously, apart from free bending also deformation of the RC element may occur, which is caused by the decrease of the concrete or reinforcing steel mechanical properties. In order to examine the contribution of the deflection caused by thermal bowing to the total deformation of the bent element with a heated tension zone, an experimental study of freely heated (unloaded) beams was performed. RC beams were heated: (1) on three sides of the cross-section or (2) only on the bottom side. Deflection of elements loaded by a substitute temperature gradient was calculated using the Maxwell–Mohr formula. The test results show that deflection of freely heated RC beams (caused by the thermal bowing phenomenon) can be 10 to 20% of the total deflection of loaded RC beams with a heated tension zone.