Study On Preparation And Performance Influencing Factors Of Air-tight Concrete

Most of the rock layers that tunnels pass through in the western region of China contain high concentrations of gas.In order to prevent gas leakage when building tunnels that pass through gas rock layers,it is often necessary to use air-tight concrete in the tunnel lining layer.The concrete materials used in the construction of nuclear power plants put forward higher requirements,and air-tight concrete is widely used due to its high resistance to gas penetration.This paper mainly studies the influence of different water-binder ratios,admixtures and admixtures on the working performance,mechanical properties and air permeability of air-tight concrete.Under the action of admixtures,the internal pore structure of concrete changes,and the internal reasons for the change of concrete air permeability coefficient are analyzed.The main research results are as follows:（1）The strength of air-tight concrete decreases with the increase of the water-binder ratio.The water-binder ratio increases from 0.45 to 0.6,and the concrete strength decreases by 34.0%.The strength of the non-water-reducing air-tightening agent is better than that of the water-reducing air-tightening agent,and it is increased by 15.9%at the age of 28 days;the early strength of concrete decreases with the increase of the fly ash content,and the powder Compared with the benchmark group,the 14d compressive strength of air-tight concrete with 30%fly ash content decreased by 28.3%.（2）The air permeability of concrete can be improved by adding water reducer and airtight agent.Compared with the benchmark concrete,the air permeability coefficient is reduced by 24.1%when the water reducer is added alone.When the strength grade is C30,the air permeability coefficient is 1.45×10^-11cm/s;Compared with the non-water reducing airtight agent,the water-reducing airtightness improves the air permeability resistance of concrete more greatly.Compared with the benchmark concrete,the air permeability coefficient is reduced by 49.2%.When the strength grade is C30,The air permeability coefficient is 0.97×10^-11cm/s;the combination of water reducing agent and water reducing air tightness agent can further reduce the air permeability coefficient of concrete and improve the air permeability resistance.（3）Fly ash has a negative effect on the air permeability resistance of concrete.The air permeability coefficient of concrete increases with the increase of fly ash content.When the fly ash content increases from 15%to 30%,the air permeability coefficient of concrete increases by 26.2%.,when the strength grade is C30,the air permeability coefficient is 15.9×10^-11cm/s cm/s,the air permeability resistance of concrete increases with the increase of silica fume content,and the silica fume content increases from 5%to10%,the air permeability coefficient of concrete It is reduced by 22.7%,and the air permeability coefficient is 3.4×10^-11cm/s when the strength grade is C30.（4）Under the conditions of this experiment,the air permeability of concrete is significantly affected by the water-binder ratio.When the water-binder ratio decreases from 0.60 to 0.45,the air permeability of concrete decreases by 89.2%.When the water-binder ratio is 0.6,the air permeability of concrete is 3.9×10^-11cm/s,when the water-binder ratio is 0.45,the air permeability coefficient of concrete is 0.4×10^-11cm/s.（5）Increasing the test pressure of air permeability coefficient will slightly reduce the air permeability coefficient of concrete under the condition that the water-to-binder ratio is lower than 0.50.After adding SL-3 non-water-reducing airtight agent,the air permeability coefficient of concrete at 0.6MPa for 28 days is higher than that of 0.3MPa.12.24%,the air permeability coefficient is 1.3×10-11cm/s.（6）The compressive strength of concrete has a binomial relationship with the air permeability coefficient.The correlation is the highest at the age of 14 days,and the correlation coefficient is 0.997.The coefficient is reduced by 0.424.（7）The airtight agent affects the air permeability of concrete by affecting the porosity,average pore size and most probable pore size of the concrete.Compared with the benchmark concrete,the porosity of concrete with type air tightness agent is reduced by 1.38%,the average pore size is reduced by 0.56nm,the most probable pore size is reduced by 1.51nm,the air permeability coefficient is reduced by 49.2%,and the air permeability coefficient is 0.97×10^-11cm/s.