Study On Mechanic And Shrinkage Properties Of Basalt Fiber Mixed Aggregates Concrete

How to reduce the shrinkage and cracking of concrete has always been a difficult problem for the engineers.Concrete with good volume stability and durability will have great application value in the fields of construction and bridge engineering.The compositional characteristics of the mixed aggregates have the dual properties of strength close to that of ordinary concrete and the conservation of lightweight aggregate concrete,and basalt fiber is increasingly used as a case where it is used to enhance the concrete to exert crack resistance.In this paper,the influence of the composites of basalt fiber and lightweight aggregates on the mechanical properties and shrinkage of concrete was studied.The durability design was used to verify the rationality of the composition design.The main research results of this article are:(1)By designing orthogonal test of the slump,compressive strength,and split tensile strength of the concrete were determined with basalt fiber content,light aggregate content and fly-ash content were the main influencing factors.The results show that: The basalt fiber content is the most significant in the slump and tensile tests.Adding basalt fiber reduces the slump of the concrete,increases the tensile strength,and increases the compressive strength;light aggregate The volume substitution ratio is the most significant in the compression test.The addition of lightweight aggregates reduces the concrete slump,compressive strength and tensile strength,but when the lightweight aggregate content is 50%,the mixed aggregate concrete compresses.The decrease of tensile strength is the least;the addition of fly ash improves the fluidity,but when the content exceeds 20%,the increase of slump decreases.The relationship between the content of the three factors and the compressive strength and tensile strength was obtained by using multiple linear regression,and the relationship between compressive strength and tensile strength of the mixed aggregate concrete was established.Based on multi-index weighted calculations,the improved efficacy coefficient method is preferred for orthogonal test results,and the optimal mix ratio is recommended based on the total efficacy coefficient.(2)By studying the pre-wetting time of lightweight aggregate,light aggregate content and the basalt fiber content on the drying shrinkage of the mixed aggregate concrete,the results show that the longer the pre-wetting time of the lightweight aggregate is,the more significant the reduction effect of the concrete is.The lightweight aggregates after pre-wetting for 24 hours were significantly better than those without pre-wetting;the internal curing effect of lightweight aggregates did not prevent the increase of the shrinkage rate of concrete in the later period,and the earlier shrinkage was better than the latter.The earlier the lightweight aggregate content is,the better the internal curing effect is,and the shrinkage effect is obvious;after a certain age period,the appropriate replacement ratio of lightweight aggregate is beneficial to reduce the concrete shrinkage rate,and the light aggregate aggregate is too much to shrink the concrete.It has a negative effect.When the concrete shrinkage rate is the lowest,the replacement rate of the best concrete lightweight aggregate is about 40%;the basalt fiber and lightweight aggregates can reduce the shrinkage of the concrete to a certain extent in the late stage of compounding,but the basalt fiber mixes the bone.The improvement of the concrete shrinkage effect is not satisfactory.(3)Using slab crack test to study the effect of light aggregate content,basalt fiber content and fiber length on the plastic shrinkage of the mixed aggregate concrete.The results show that the addition of light aggregates significantly prolongs the cracking time of the concrete.Both the area of cracking and the number of cracks have been significantly reduced,and fine cracks have increased.With the increase of basalt fiber content,the initial cracking time of mixed-aggregate concrete prolonged,and the total cracking area,the number of cracking cracks,and the average cracking area of cracks all showed a significant downward trend.The addition of basalt fiber reduces the maximum crack width and number of cracks in the mixed aggregate concrete.The effect is best when the fiber content is 0.1%,and the optimization performance decreases when the amount of fiber is added;when the volume of basalt fiber is 0.1%,As the length increases,the crack resistance effect increases first and then decreases.The basalt fiber with a length of 20 mm has the best anti-cracking effect.(4)The same experimental conditions as the plastic shrinkage were set,and the durability test of basalt fiber-mixed aggregate concrete was carried out based on the RCM anti-chloride ion permeability coefficient method.The results showed that: the resistance to chloride ion permeability and crack resistance of mixed aggregate concrete There is good consistency in performance.The larger the replacement ratio of light aggregate,the smaller the chloride diffusion coefficient,and the best basalt fiber is 0.1% and the length is 20mm.