Study On Compressive Strength And Frost Resistance Durability Of PVA Fiber Reinforced Concrete Under Freeze-thaw Cycles

Since the 20th century,the durability of concrete structures has been the focus of research in the field of civil engineering at home and abroad.In China,especially in the northern part of the country,the temperature changes dramatically with the change of seasons,which makes the concrete structure suffer from the freeze-thaw damage for a long time,resulting in the serious reduction of its safety and durability.The research shows that PVA fiber can effectively enhance the crack resistance,water freezing resistance and salt freezing corrosion resistance of ordinary concrete.With the continuous development and progress of China's economic technology,the application of PVA fiber concrete has been continuously promoted,but the current research on PVA fiber concrete In particular,there are relatively few studies on the durability of frost resistance,so it is of great significance to study the improvement of concrete properties and the practical application and promotion of this new type of high-strength,high-elasticity,acid-alkali-resistant synthetic fiber.In this paper,through the study of PVA fiber concrete under different mixing ratios,the mechanical properties of PVA fiber reinforced concrete with compressive strength as index and the frost resistance durability with apparent form,mass loss rate and relative dynamic modulus as index are studied by combining the static test and freeze-thaw cycle test,and the uniaxial properties of concrete after freeze-thaw cycle are studied by combining the ultrasonic testing and other technical means.The main research contents are as follows:?1?The rapid freeze-thaw cycle test was conducted,taking the amount of raw materials,the freeze-thaw medium solution and the number of freeze-thaw cycles as the main variables.PVA fiber reinforced concrete was tested in three freeze-thaw media solutions:water,3.5%Na₂SO₄ solution and MgSO₄ solution.After 0,50,100 and 150freeze-thaw cycles,the apparent shape,mass loss rate,relative dynamic elastic modulus and cube compressive strength of PVA fiber reinforced concrete were studied and analyzed.It is concluded that the concrete added with bentonite and large amount of fly ash is more susceptible to freeze-thaw erosion damage after undergoing freeze-thaw cycles,and the mechanical properties and freeze-thaw durability are reduced by the addition of both of bentonite and fly ash.The macro test results show that:among the three freeze-thaw media solutions,3.5%Na₂SO₄ solution has the most serious freeze-thaw erosion damage to the concrete,while the water is the least;?2?Salt solution accelerated the strength attenuation of concrete,among which3.5%Na₂SO₄ solution had the most serious damage to the strength of concrete,and the lightest was water;Study the influence of freeze-thaw cycle erosion on the mechanical properties of PVA fiber concrete.Through the analysis of the compressive strength values before and after the freeze-thaw cycle,it is concluded thatthe loss of compressive strength increases with the freeze-thaw cycle.The addition of bentonite and fly ash accelerates the generation and development of internal cracks of concrete,and also increases the decay rate of compressive strength of concrete.Salt solution accelerates the strength decay of concrete.Among them,3.5%Na₂SO₄ solution has the most severe damage to concrete strength,and the lightest is water;?3?The damage variable is introduced to express the internal damage degree of concrete specimen after freeze-thaw cycle erosion.Finally,according to the principle of least square method and the definition of concrete damage variable,a PVA fiber reinforced concrete freeze-thaw damage evolution model based on Weibull probability distribution is established and verified.The results show that the damage model selected in this paper can better describe the whole freeze-thaw damage evolution process.