Study On The Coupling Effect Of Uniaxial Continuous Load And Freeze-thaw Cycles On The Durability Of Concrete

The durability of concrete is a hot research field of civil engineering at home and abroad.The durability of concrete structure is often the result of coupling of many factors.Concrete buildings in northern cold areas and parts of South China are subjected to self weight loads and external loads,and also suffer from freeze-thaw cycles.The coupling action of load and freeze-thaw cycle accelerates the damage and deterioration of concrete.Finally,this coupling will lead to cracking of concrete,corrosion of reinforcement and reduction of the strength of building structure.And the damage of concrete structure occurs before the design life is reached.In this paper,the durability of concrete under load-freeze-thaw coupling is studied.The damage law of concrete under coupling is analyzed.The pressure state of the concrete structure in the actual project is simulated by the self-designed loading device.The rapid freeze-thaw cycle test of ordinary concrete block and air entraining concrete block(containing air content 5%)was carried out.The stress level of the test block includes three kinds,0fc,0.3fc,0.5fc(fc is the ultimate stress).The durability of concrete under the coupling action of sustained load and freeze-thaw cycle is analyzed.The research contents include:(1)According to the concrete compression mode in the actual project,the load is applied to the concrete block by the self-designed loading device.The mass loss and relative dynamic modulus of elasticity of concrete specimens were measured.The macroscopic damage degree of concrete specimen under the action of load freeze-thaw cycles is analyzed.The results show that compared with air entraining concrete block,the damage degree of common concrete specimen is smaller under the action of load freeze-thaw cycle coupling.In addition,under the same freeze-thaw cycles,the damage degree of concrete specimen doesn't increase with the increase of stress level.(2)The capillary water absorption of concrete under the action of freeze-thaw cycles is tested to study the influence of stress level and freeze-thaw cycles on the frost resistance of concrete.It is found that the capillary water absorption and the initial capillary water absorption coefficient increase with the increase of the freeze-thaw cycle when the stress level is constant.When the stress of the concrete specimen is less than the critical stress,the load applied to the concrete test block is beneficial to improve the structure frost resistance.However,when the stress is greater than the critical stress,the coupling of the load and the freeze-thaw cycle will aggravate the degree of deterioration of the concrete.(3)The permeation test of the concrete specimen under the action of load-freezing-thawing cycle was measured by using the self-designed infiltration experiment device.And the permeability coefficient is calculated.The effect of external load,freeze-thaw cycle,load-freeze-thaw cycle coupling on the impermeability of concrete is analyzed.The results show that the change law of concrete permeability is the same as the change of capillary water absorption performance.(4)The pore structure characteristics of concrete under the action of load freeze-thaw cycles are studied by mercury intrusion test.According to the change of micro pore structure,the variation law of capillary water absorption and permeability of concrete is analyzed.The change law of concrete physical properties is analyzed from pore diameter distribution and porosity change process.The results show that the change rule of the physical properties is basically consistent with the actual permeability and capillary water absorption.