Study On The Damage Of Concrete Caused By High Water Pressure And The Acceleration Effect Of Chloride Transport

In the underground environment or marine environment,with the increase of the depth,the concrete environment is worse.High water pressure will damage the concrete structure,and high water head will accelerate the harmful salt into the concrete.Chloride is a serious factor in the durability research of reinforced concrete.The source of chloride is universal and its harm is great.How to prevent the erosion of chloride under water head pressure is a major issue at present.The underground structure has been eroded by high water pressure and harmful salt solution for a long time.The static water pressure destroys the internal pore structure of the concrete,resulting in the decline of the overall mechanical properties of the concrete.In this paper,the attenuation laws of ultrasonic wave for testing sound velocity,rebound value,splitting tensile strength and compressive strength of ordinary concrete with three kinds of water cement ratio and four kinds of nano silica modified concrete with different nano content under different hydraulic pressure levels of 0MPa,1.2MPa,2.4MPa and 3.6MPa are studied.The attenuation laws are obtained and the attenuation model is established.For the modified concrete with different nano dosage,the experimental study of ultrasonic testing sound velocity and splitting tensile strength with different water pressure and different penetration time is carried out.The optimal dosage is 1%,which makes the decline rate of compressive strength and ultrasonic testing sound velocity and splitting tensile strength slowest.The results show that the splitting tensile strength and compressive strength of ordinary concrete decrease with the continuous effect of water pressure.The larger the water pressure is,the more obvious the strength attenuation is.The results show that the main reason for the decrease of the mechanical properties of concrete is the decrease of the density and the increase of the porosity.Through the electron microscope scanning and mercury injection experiment,it is found that the damage micro cracks and connected holes increase gradually with the continuous action of water pressure,and the concrete hardness and compactness decrease with the continuous action of water pressure.The strength attenuation model of concrete under the action of high water pressure is found.In the study of chloride ion transport in concrete under high water pressure,the permeability tests of four gradients(0MPa,1.2MPa,2.4MPa,3.6MPa)were carried out.The distribution of chloride ion was obtained by four gradient permeability tests and rapid determination of chloride ion.By analyzing the experimental data of seepage height and seepage volume,the law of seepage volume and seepage height under different water cement ratio,seepage time and water pressure is obtained and the model is established.Based on Darcy's law and reverse osmosis theory,a water transport model and a spatiotemporal distribution model of chloride ions are established.Through the modification of concrete with nano silica,the transport law of chloride and water in the modified concrete was studied.Four kinds of nano silicon oxide(0%,0.5%,1%,2%)and four water pressure gradients(0MPa,1.2MPa,2.4MPa,3.6MPa)were used in the penetration test.The penetration test of four water pressure gradients was carried out with 10% sodium chloride solution.The distribution law of chloride ion was obtained by the determination of chloride ion.Through the measurement of water seepage,the change rule and model of water seepage are obtained.According to the mechanism of reverse osmosis,with reference to the experimental data,the influence coefficient of nano dosage is introduced,and the theoretical analysis of chloride ion transport with nano proportion is obtained.The experimental results show that the nano silica modified concrete can improve the damage of concrete under high water pressure,restrain the transfer rate of chloride ions to the concrete under high water pressure,and obtain the optimal content of Nano-SiO2 is 1%,and the effect of improvement is the most obvious.Through SEM,mercury injection test and control group,the impermeability of nano silicon oxide modified concrete was improved under the continuous action of high water pressure,and the internal damage of concrete was effectively inhibited.The impermeability and mechanical properties of nano silicon oxide modified concrete,which were significantly improved.The paper has 53 figures,27 tables and 129 references.