Experimental Study On Salt Frost Resistance Of Basalt Fiber Fine Aggregate Concrete

In the cold and dry areas of Northwest China,concrete buildings under the combined action of long-term freeze-thaw and erosion have the problems of slag falling,cracking and durability degradation,which seriously affect the actual benefits of water conservancy projects.Fine aggregate concrete has the advantages of easy access to materials,uniform and stable,good compactness,high degree of freedom in structural design,and is more and more widely used in engineering practice.Adding a certain amount of basalt fiber into fine aggregate concrete can enhance its overall performance.In order to obtain the optimal volume content of basalt fiber and explore the influence of basalt fiber volume content on the durability of fine aggregate concrete structure,the salt frost resistance of basalt fiber fine aggregate concrete was studied.In this paper,Jingdian Irrigation Area in Gansu Province is taken as a typical study area,and the main causes of damage are determined by field investigation.Basalt fiber is selected as the reinforcement material of fine aggregate concrete to simulate the field environment of irrigation area,and the salt frost erosion test is carried out by"quick freezing method".By measuring the mass loss,compressive strength and dynamic modulus of elasticity of basalt fiber fine aggregate concrete under different freeze-thaw media（clear water,5%Na2SO4solution,3%Na Cl solution）,the durability degradation law of basalt fiber fine aggregate concrete under different basalt fiber volume content（0,0.05%,0.1%,0.15%,0.2%）is clarified;the durability degradation law of basalt fiber fine aggregate concrete under salt freeze condition is measured by ultrasonic method and nuclear magnetic equipment The change of internal defects and internal pores of Wuyan fiber-reinforced fine aggregate concrete leads to its meso deterioration law.The fitting model of fractal dimension and compressive strength and the mechanical damage model of damage degree and compressive strength are established,and the performance correlation is studied,which provides a method for the later maintenance and structural safety assessment of concrete structures in cold and dry areas.The main conclusions are as follows:（1）Under salt-frozen conditions,the addition of basalt can effectively improve the apparent damage of fine stone concrete.The quality and relative dynamic elastic modulus of basalt fiber fine stone concrete decrease with the increase of freezing times.The addition of basalt fiber can delay the decline of mass and dynamic elastic modulus of fine aggregate concrete after salt freezing to a certain extent,and the fine aggregate concrete with basalt fiber volume content of 0.15%has the best salt freezing resistance.（2）Adding a certain amount of basalt fiber into fine aggregate concrete can improve its initial compressive strength to a certain extent,but excessive amount will lead to the decrease of compressive strength.When the volume fraction of fiber is 0.15%,the compressive strength is improved by 8.69%.Basalt fiber can reduce the decline rate of compressive strength of fine aggregate concrete after salt freezing,but it can not prevent the damage of mechanical properties caused by salt freezing.The optimal volume of basalt fiber is between0.15%and 0.2%.（3）Under three kinds of freeze-thaw erosion media,the damage of basalt fiber fine stone concrete caused by salt freezing is the most serious in 3%Na Cl solution,followed by 5%Na₂SO₄ solution and the smallest in clean water.The damage degree of basalt fiber fine stone concrete is ranked as 3%Na Cl Solution>5%Na₂SO₄ Solution>clear water.（4）The variation regularity of internal defects and porosity of basalt fiber fine stone concrete under salt freezing is consistent with that of durability index.The addition of basalt fibers can improve the internal pore distribution of fine stone concrete.The basalt fibre fine stone concrete with 0.15%fiber volume has the smallest T₂ spectrum total area,the smallest pore volume and the highest internal compactness,and the slowest transformation speed from small pore to large pore with salt freezing.The fractal dimension D is used to characterize the complexity of pore size distribution structure in basalt fiber fine stone concrete.With the increase of the number of freezing times,the larger the fractal dimension is,the more the harmful pore and the harmful pore distribute,the lower the salt-freezing resistance will be.（5）The fitting model of fractal dimension and compressive strength and the mechanical property damage model of damage degree and relative compressive strength are established.The experimental data show that the fitting accuracy is high and the applicability of the model is strong.The relationship between pore distribution characteristics and compressive strength of fine aggregate concrete is clarified.With the help of dynamic elastic modulus,the relative compressive strength of concrete structure in cold and dry areas can be calculated by dynamic elastic modulus.