Experimental Research On Mechanical Properties And Frost Resistance And Dry Shrinkage Of Basalt Fiber Recycled Aggregate Concrete

With the continuous increase of waste concrete,the problem of environmental degradation has become increasingly severe.The recycled concrete has become a hot topic for researchers at home and abroad.Therefore,based on the orthogonal test method,the author selects the basalt fiber content,the substitution rate of recycled aggregate,and the replacement rate of fly ash as the factors,and the compressive strength,splitting tensile strength,and flexural strength for the C30 recycled coarse aggregate concrete were studied.In addition,the recycled coarse aggregates modification,basalt fiber aspect ratio and recycled aggregate replacement rate were tested for frost resistance and drying shrinkage.From a microscopic point of view,the mechanism of fiber action was explored by SEM.It is hoped that it will provide a theoretical basis for future concrete works.The main work and conclusions are as follows:(1)Through statistics and analysis of the orthogonal test results,the best dosage is obtained:Basalt fiber content is 0.3%,recycled coarse aggregate replacement rate is 20%and fly ash content is 20%.(2)Based on the best dosage,the influence of recycled coarse aggregate with diluted hydrochloric acid soaked by 3%mass fraction and basalt fiber aspect ratio about the compressive strength,splitting tensile strength,and flexural strength of basalt fiber recycled aggregate concrete was investigated.Besides,the SEM test analysis of the fiber action mechanism and fiber mixing method was performed.The results showed that:①Compared with non-immersion group,the compressive strength of the modified group has been greatly improved,while the splitting tensile strength and flexural strength have not improved obviously.②The compressive strength reached the best when the aspect ratio was 1100,and the flexural strength and compressive strength trends are consistent.For the splitting tensile strength,as the fiber aspect ratio increased,the splitting Tensile strength shows an increasing trend.③The optirmized way to wrap the paste is superior to the straight doping way,and it fully exerts the effect of basalt fiber to prevent cracks.(3)The effects of recycled coarse aggregate modification and fiber aspect ratio on frost resistance of basalt fiber recycled aggregate concrete were studied.The results showed that:①the mass loss rate of the modified group,the optimal group and the benchmark group shows a different degree of growth with the increase of the number of freeze-thaw cycles;For the relative dynamic modulus,the optimal group and the modified group,the overall downward trend is more gentle,while the relative dynamic modulus of the benchmark group downward trend is more unstable;Compared with the optimal group and the benchmark group,the modified group has better frost resistance.②When the aspect ratio of basalt fiber is 1100,the frost resistance of recycled aggregate concrete is more obvious.(4)The dry shrinkage of basalt fiber recycled aggregate concrete occurs mainly in the early stage.As the replacement rate of recycled coarse aggregate increases,the shrinkage deformation gradually grows.The basalt fiber has the obvious effect of inhibit drying shrinkage as the aspect ratio increases.