Research On Mechanical Properties Of FRHPC Subjected To Medium High-Temperature

Nuclear waste disposal is the focus of international investigations now. The heat radiated by nuclear waste for long will generate thermal field which causes thermal stress, and degrade the properties of concrete, the primary material of container made for nuclear waste, so improving the durability of concrete and analyzing the temperature field and stress status in concrete member subjected to medium high-temperature is very significative for developing storage container.The effects of short steel fiber, ultra-short steel fiber, polypropylene fiber and fly ash on the strength, toughness, impermeability of concrete under pre-or post-roasting are determined by orthogonal test, and the concrete with good impermeability is mixed by the method of steepest ascent. By test and Ansys software, the unsteady ax-symmetric temperature field of concrete cylinder is measured and simulated, then thermal stress of cylinder caused by steady ax-symmetric temperature field is analyzed by solution method.On the study of durability, the effects of short steel fiber, ultra-short steel fiber, polypropylene fiber and fly ash mixed on the properties of C50concrete under pre-or post-roasting, including slump constant, compressive strength, impermeability, flexural properties, fracture energy, are analyzed by gradation analysis and variance analysis. Basing on the impermeability of concrete under post-roasting chiefly, the content of influencing factors is adjusted, then the properties hereinbefore of the concrete obtained by the method of steepest ascent, steel fiber reinforced concrete and high strength concrete is tested. By comparison, the time for roasting the summit-impermeability concrete and high strength concrete is prolonged, then the relative permeability coefficient is regressively analyzed.By the temperature sensors deposited beforehand, the temperature and central calefactive rate in concrete cylinder which has been roasted for3or6,12hours in oven dominated by100℃or120℃are measured. Under the same condition, Ansys software is also used for the transient thermal analysis of concrete cylinder by logical loading modes, then the distributing instance of temperature field and displacement is discussed which are in accord with test.To the cylinder in the steady ax-symmetric temperature field including the inconsistent instance about heat of top and bottom, the thermal stress is analyzed for mutative axial temperature and arbitrary z-functions exterior temperature, so the full analytical solution is obtained, then the solution of undetermined coefficents is discussed using the properties of power and trigonometric function and the numerical examples about the concrete cylinder are presented by test on measuring temperature and Matlab software.Drawn from the results obtained in the study above, the conclusions are as follows: steel fiber is beneficial to improving durability of concrete; the hybrid effect of short steel fiber and ultra-short steel fiber is fine; the effect of steel fiber on durability of concrete would be better if the dispersion and bond strength with matrix is improved; with the extension of time for roasting, steel fiber-reinforced high performance concrete would be similar to high strength concrete in impermeability.