Experimental Study On Basic Properties Of Nano-reinforced Straw Fiber Recycled Concrete

Due to the rapid rise of the construction industry,building materials have been fully used,and the further use of waste concrete has become an indispensable object of discussion in daily life,so recycled concrete has been used again.According to the corresponding research,we can know that recycled concrete meets the double-layer standard for material use and structural application,but due to its own shortcomings that it is particularly prone to cracks,this is an important factor that has not yet been applied in most projects.Considering its own shortcomings,we add wheat straw into it,so that the cracks of the recycled concrete itself are suppressed,so that the crack resistance of the recycled concrete is improved.At the same time,the incorporation of nano-materials can improve the mechanical properties of the recycled concrete such as compression,durability,impermeability and frost resistance.Therefore,this paper carried out experimental research and theoretical analysis of nano-reinforced straw fiber recycled concrete.The main research content includes the following aspects:Carry out the experimental research on the performance of nano-reinforced straw fiber recycled concrete,analyze the replacement rate of recycled coarse aggregate,wheat straw fiber content,nano-Si O₂content,nano-Si O₂particle size to the specimen compressive strength,stress-strain,displacement ductility coefficient,elastic modulus.The influence of quantity,poisson’s ratio,frost resistance and impermeability.The results show that the recycled concrete is damaged by compression.When the specimen is damaged,multiple prisms are formed,which are brittle.Due to the increase in the replacement rate of recycled coarse aggregate,the time at which the straw fiber recycled concrete begins to appear cracks will also be advanced.After the cracks appear,the width will increase correspondingly,and the number of cracks will also follow the same after the occurrence of cracks.There can be obvious cracks on the surface of straw fiber recycled concrete,but the test piece has not been cut into two parts.Due to the increase in the replacement rate of recycled coarse aggregate,the time at which the straw fiber recycled concrete begins to appear cracks will also be advanced.After the cracks appear,the width will increase correspondingly,and the number of cracks will also follow the same after the occurrence of cracks.Corresponding more;because of the increase in the amount of straw,the time when the straw fiber recycled concrete starts to crack will also become very late.After the cracks appear,the width will decrease correspondingly,and the number of cracks will appear after the cracks appear.Will decrease accordingly.Nano-reinforced straw fiber recycled concrete did not show brittle failure or large cracks.After the destruction,the integrity is good and the disintegration will not occur.Due to the increase in the replacement rate of recycled coarse aggregate,the time at which the straw fiber recycled concrete begins to appear cracks will also be advanced.After the cracks appear,the width will increase correspondingly,and the number of cracks will also follow the same after the occurrence of cracks.Due to the increase in the amount of straw and NS,the time when the straw fiber recycled concrete starts to crack will become too late.After the cracks appear,the width will decrease correspondingly,and the number of cracks will increase after the cracks appear.Nanometer particle size has little effect on crack width and crack number.At different substitution rates of recycled coarse aggregates,with the increase of NS content,the compressive strength,displacement ductility coefficient,elastic modulus and poisson’s ratio of the specimens showed a law of increase first and then decrease.Under different NS dosages,as the replacement rate of the recycled coarse aggregate becomes larger,the compressive strength,displacement ductility coefficient,elastic modulus and poisson’s ratio of the specimens show a continuously changing law.At different replacement rates of recycled coarse aggregates,with the increase of the amount of straw,the changes of the compressive strength,displacement ductility coefficient,elastic modulus and poisson’s ratio of the specimens generally showed a change law that first increased and then decreased.As the substitution rate increases,the elastic phase of the specimen becomes shorter and the slope gradually decreases,indicating that the elastic modulus of the nano-reinforced straw fiber recycled concrete decreases,and the stress-strain curve is approximately a straight line.As the load continues to increase,the elastic modulus of the nano-reinforced straw fiber recycled concrete gradually decreases,the curve deviates from a straight line,and the specimen enters the elastoplastic stage.At this point the concrete began to crack,and the strain growth began to accelerate.Because it is nano-reinforced straw fiber recycled concrete,there are few pores in the concrete,which makes the test piece stress-strain relationship curve rise section without obvious inflection point.As the load continues to increase,the cracks of the test piece continue to develop.When the test piece reaches the limit stress,the strain of the test piece increases rapidly.The greater the replacement rate,the slower the strain growth rate.This indicates that the replacement rate of recycled coarse aggregate is greater.The greater the brittleness of the piece,the final concrete is crushed and the test piece is destroyed.In this paper,the durability test of nano-reinforced straw fiber recycled concrete is carried out.The results show that under different freeze-thaw cycles,with the increase of NS content,the mass loss rate,relative dynamic elastic modulus loss rate and strength loss of the specimen first decrease and then increase.Under different NS dosages,as the number of freeze-thaw cycles increases,the mass loss rate,relative dynamic elastic modulus loss rate and strength loss rate of the specimens continue to increase.Under different freezing and thawing cycles,with the increase of the amount of straw,the mass loss rate,relative dynamic elastic modulus loss rate and strength loss rate of the specimen decreased first and then increased.At different replacement rates of recycled coarse aggregate,with the increase of NS content,the height of the specimen decreased first and then increased.Under different NS dosages,as the replacement rate of the recycled coarse aggregate becomes larger,the height of the drop of the test piece increases continuously.Under different replacement rates of recycled coarse aggregates,with the increase of the amount of straw,the drop height of the test piece decreases first and then increases.Microscopic analysis shows that the intensity of the C₃S and C₂S diffraction peaks of the 1.0%～3.0%NS content group is greater than that of the benchmark group at 14d and 28d,indicating that the effect of promoting the hydration of cement is limited when the amount of nano-Si O₂is large,because of this The phenomenon of nano-Si O₂agglomeration is more serious.The 1.0%NS content group C-S-H gel grows alternately within 10μm from the aggregate surface with nano-Si O₂as the nucleus to form a cluster structure.The 2.0%and 3.0%NS content groups are within20μm from the aggregate surface,and are mainly composed of network C-S-H gel and fine-grained C-S-H gel.Aggregate-cement stone in the 0.5%～2.0%NS content group is tightly bound,and almost no cracks between the two are seen.Both the 2.5%and 3.0%NS content groups have cracks extending from the aggregate surface to the interface transition zone.This is because excessive nano-Si O₂content causes excessive drying shrinkage and cracking in the late stage of cement hydration.On the basis of experimental research,considering the influence of the replacement rate of recycled coarse aggregate,the content of wheat straw fiber,the content of nano-Si O₂,and the particle size of nano-Si O₂,the strength influence coefficient related to the nanometer age and the influence of the straw fiber age are introduced.The relative strength influence coefficients are used to establish a calculation model for the compressive strength of nano-reinforced straw fiber recycled concrete cubes.On the basis of experimental research,considering the influence of recycled coarse aggregate replacement rate,wheat straw fiber content,nano Si O₂content,and nano Si O₂particle size,the fiber reduction factor is introduced,and the peak stress of nano-reinforced straw fiber recycled concrete prism is proposed.Elastic modulus,peak strain,Poisson’s ratio,displacement ductility coefficient calculation formula.On this basis,considering the influence of the replacement rate of recycled coarse aggregate,the content of wheat straw fiber,the content of nano-Si O₂,and the particle size of nano-Si O₂,the dimensionless vertical control parameters related to the vertical curve and the dimensionless related to the horizontal curve are introduced.Lateral control parameters,establish the stress-strain relationship model of nano-reinforced straw fiber recycled concrete column.According to the influence of the experimental research results and considering the damage mechanics formula,hydrostatic pressure formula and osmotic pressure formula,the whole process of freeze-thaw damage of nano-reinforced straw fiber recycled concrete is exposed.In the case of considering the fatigue damage formula,and considering the effect of nano content and straw content on the frost resistance of nano-reinforced straw fiber recycled concrete,the introduction of nano-reinforced straw fiber recycled concrete in the case of freeze-thaw damage.The nano-influence coefficient factor and the straw fiber influence coefficient factor are used to obtain the freeze-thaw damage evolution formula of nano-reinforced straw fiber recycled concrete.According to the influence of the experimental research results,under the premise of considering the fatigue damage formula and the Newtonian material cooling formula,then consider the influence of the nanometer content and the straw content on the frost resistance of the nano-reinforced straw fiber recycled concrete,and the introduction of nano-reinforcement straw fiber recycled concrete is damaged due to freeze-thaw cycles in a freeze-thaw environment and is related to the strength-related coefficient factor.It is concluded that the nano-reinforced straw fiber recycled concrete is damaged due to freeze-thaw cycles in a freeze-thaw environment.Life estimation model.