Study On The Influence Of Hybrid Fibers On The Propertise Of Recycled Concrete

Recycled concrete itself has some defects,such as large crushing index,poor adhesion with the matrix,poor toughness and so on,which limits its application scope.The research shows that adding some fibers into recycled concrete can improve the performance of recycled concrete.In this paper,polyvinyl alcohol fiber with high elongation and basalt fiber with high elastic modulus are mixed into recycled concrete to modify it,and the influence law of two kinds of fiber on the working performance,mechanical properties and durability of recycled concrete under three volume dosage of 0.1%,0.2%and 0.3%and four mixing ratios of 1:4,1:2,1:1,2:1 and 4:1 is explored,Finally,the optimal amount and ratio of fiber are determined to provide theoretical guidance for practical engineering application.Finally,from the micro point of view,the paper analyzes the improvement mechanism of mixed fiber on recycled concrete performance.The research contents of this paper are as follows:(1)The slump test of recycled concrete with different fiber content is carried out.The results show that the slump of recycled concrete is reduced when fiber is added into recycled concrete either in single or mixed way,and the slump value gradually decreases with the increase of fiber content.(2)The basic mechanical properties of recycled concrete mixed with basalt fiber,polyvinyl alcohol fiber and two kinds of fiber are tested.The results show that the compressive performance of recycled concrete is slightly improved,while the splitting resistance and tensile performance of recycled concrete are improved.When the total volume of fiber is 0.2%,the ratio of polyvinyl alcohol fiber and basalt fiber is 1:1 When the content of PVA fiber and basalt fiber is 0.3%and the ratio of PVA fiber and basalt fiber is 4:1,the three basic mechanical properties of recycled concrete are relatively high and better than single fiber,showing a good mixing effect.(3)The appearance change,mass loss rate,relative dynamic elastic modulus loss rate and compressive strength loss rate of recycled concrete with different fiber content under different freeze-thaw cycles are tested,and the mixing proportion and content of two kinds of fibers are obtained when the frost resistance is the strongest.The mass loss rate,relative dynamic elastic modulus loss rate and compressive strength loss rate of recycled concrete with different fiber content under different sulfate drying and wetting cycles are studied,and the mixing proportion and content of two kinds of fibers are obtained when the sulfate corrosion resistance is the strongest.Taking ordinary recycled concrete,0.2%PVA fiber and recycled concrete with 0.2%PVA fiber and 1:2,1:1,2:1 ratio as the research object,the strength attenuation of recycled concrete under rapid freeze-thaw condition and the quality loss of recycled concrete under sulfate attack were studied.The results show that the recycled concrete with these five kinds of fiber content needs 450 times,689 times,761 times,919 times and 871 times of freeze-thaw cycles respectively when it completely loses its compressive capacity under freeze-thaw condition,and 91 times,96 times,106 times,105 times and 109 times of sulfate drying and wetting cycles respectively when its mass and initial mass are the same under sulfate attack condition.(4)Through the basic mechanical properties test and durability test results of the recycled concrete with mixed fiber,it can be seen that the total volume content of the two fibers is 0.2%,and the mixing ratio is 1:1,and the effect is better than that of the single fiber,showing good mixing effect.The results can provide reference for practical engineering application.(5)The microstructure of fiber recycled concrete was observed by SEM,and the mechanism of fiber performance improvement was analyzed from the aspects of fiber bond force and crack resistance by combining the fiber spacing theory.The ratio of pulling out work and fracture work of different fibers was calculated by the energy dissipation mechanism of fiber,and the different roles of different fibers in recycled concrete were analyzed.