Effect of High Temperature on Reinforced One-Way Self- Compacting Concrete Slab Specimens

Abstract

This research is devoted to investigate the behaviour of reinforced one-way self-compacting concrete slab specimens exposed to fire flame and the properties of the self-compacting concrete after exposed to fire. The exposure of reinforced one-way self-compacting concrete slab specimens to fire flame causes changes in their behaviour and properties. The experimental work includes burning the control specimens (cubes and prisms) and the slab specimens from both sides at three temperature levels (300, 500 and 700°C) by fire flame furnace for the same time period (1 hour) then cooling them in two methods. The first was by cooling the burned specimens gradually by leaving them in air (laboratory condition) and the second method was suddenly by spraying the burned samples by water. Then the specimens were loaded till failure by hydraulic applied load machine. After that, the experimental results were discussed with results of the reference specimens (non-burned). The mechanical properties (compressive strength and modulus of rupture) of specimens were determined and discussed after exposing the specimens to fire flame at temperature levels of (300, 500 and 700°C) for (1hour) at age of (28days) then cooling and testing them. The relations of the load – mid-span point deflection, the maximum residual load – temperatures and the weights of slab specimens – temperature were determined and discussed with the effects of temperature, compressive strength and cooling method on these relations. Based on test results, the properties of concrete were affected by the exposure to fire flame and they were decreasing as the fire temperature was increasing. The compressive strength of concrete was decreasing with increasing the temperature and the values of compressive strength for the cubes cooled suddenly were less than the others cooled gradually. Also, the values of modulus of rupture for the concrete prisms were decreasing and they were less for the prisms cooled suddenly than the others cooled gradually. (III) The residual maximum load capacity of slab specimens also decreased significantly with the exposure to fire flame by an amount depending on the exposure temperature, cooling method and compressive strength of concrete. For the slab specimens of compressive strength of (f 'c= 20MPa), the percentages of residual maximum load capacity of slab specimens after exposure to temperature levels of (300, 500 and 700 °C) were about (81.5%, 75% and 62.3%) for gradual cooling and they were about (77.9%, 68.3% and 58.3%) for sudden cooling. For the slab specimens of (f 'c =30MPa), the percentages of residual maximum load capacity of slab specimens after exposure to temperature levels of (300, 500 and 700 °C) were about (85.7%, 83.5% and 72.3%) for gradual cooling and they were about (85%, 77.3% and 56.4%) for sudden cooling. For the slab specimens of (f 'c =40MPa), the percentages of residual maximum load capacity of slab specimens after exposure to temperature levels of (300, 500 and 700 °C) were about (92.3%, 85.7% and 71.4%) for gradual cooling and they were about (90%, 79.1% and 64.2%) for sudden cooling. With respect to the theoretical study, it includes a theoretical analysis to determine the reduction factor that relates the bending strength after exposing the slab specimens to high temperature (fire flame) and the bending strength of slab specimens that were not exposed to high temperature (reference slab specimens). Based on the results of this study, the bending strength for any reinforced one-way self-compacting concrete slab of any compressive strength and any fire temperature may be estimated at future by using equations (16) and (17) presented in Chapter Five