Study On Rheological Properties Of Nano-SiO₂ And PVA Fiber Reinforced Cementitious Composites

With the continuous progress of society,the building structure form is developing towards the direction of super-high,long-span and complex,and the traditional cementitious composites are not enough to meet the engineering requirements.Therefore,the disadvantages of cement-based materials such as low toughness,high brittleness,poor anti-deformation ability and insufficient durability were improved by adding the nano-SiO₂ and PVA fibers.Among them,nano-SiO₂ and PVA fibers are the commonly used modified and enhanced admixes of cementitious composites.In recent years,the extensive application of pumping cementitious composites has put forward higher requirements for the rheological properties of cementitious composites.The rheological properties of cementitious composites affect the casting and molding process,and inappropriate consistency and workability may lead to the problems of segregation and bleeding of newly mixed cementitious composites.In the long run,it will affect the strength and durability of hardened cementitious composites.The addition of Ganamir particles and fiber materials can effectively improve the properties of cementitious composites,and also have a great influence on the rheological properties of the newly mixed cementitious composites.In view of this,the effects of nano-SiO₂ and PVA fibers on the rheological properties and workability of cementitious composites were studied in this study through the rheological test,laminar flow test,slump expansion test,bleeding rate test and cube compressive strength test of freshly mixed cementitious composites.The main research contents and results of this study are as follows:（1）The rheological parameters such as static yield stress,dynamic yield stress,plastic viscosity,yield stress of lubrication layer and viscosity of lubrication layer were measured through the rheological test of freshly mixed cementitious composites and the lubrication laminar flow test.The influence of nano-SiO₂ and PVA fiber on the rheological properties of freshly mixed cementitious composites was analyzed,and the corresponding influence rules were obtained,and the influence mechanism of nano-SiO₂,PVA fiber and polycarboxylate superplasticizer on the rheological properties of freshly mixed cementitious composites was revealed.The results show that the static yield stress,the dynamic yield stress,the plastic viscosity and the viscosity of the lubrication layer decrease first and then increase with the addition of nano-SiO₂.With the addition of PVA fiber,the static yield stress,dynamic yield stress,plastic viscosity and lubrication layer viscosity of the newly mixed cementitious composites increase gradually.With the addition of polycarboxylate superplasticizer,the static yield stress,the dynamic yield stress,the plastic viscosity and the viscosity of the lubrication layer of the newly mixed cementitious composites decrease gradually.（2）Through the slump extending degree,have had a new mix slump extending degree of cementitious composites materials,analyzed the SiO₂,PVA fiber and polycarboxylate superplasticizer on the properties of new mixing cementitious composites material flow,and draw the corresponding influence law,reveals the nano SiO₂,PVA fiber and polycarboxylate superplasticizer of cement matrix composite slump extending degree,the influence mechanism.The results show that with the addition of nano-SiO₂ and PVA fibers,the slump propagation of the newly mixed cementitious composites decreases gradually,and with the increase of the content of polycarboxylate superplasticizer,the slump propagation of the newly mixed cementitious composites increases gradually.（3）Through exudation rate test,have had a new mix cementitious composites exudation rate,analyzed the SiO₂,PVA fiber and polycarboxylate superplasticizer for the new mix cementitious composites slump extending degree of influence,and draw the corresponding influence law,reveals the nano-SiO₂,PVA fiber and polycarboxylate superplasticizer of cement matrix composite slump extending degree,the influence mechanism.The results showed that with the increase of nano-SiO₂ and PVA fiber content,the bleeding rate of the newly mixed cement-based composites decreased gradually.With the increase of polycarboxylate superplasticizer,the bleeding rate of the newly mixed cementitious composites increased gradually.（4）Through the consistency test,test found new mix cementitious composites cone and cone into the degree of differenceΔH,analyzed the SiO₂,PVA fiber and polycarboxylate superplasticizer for the new mix cementitious composites material consistency and the influence of thixotropy,reveals the nano SiO₂,PVA fiber and polycarboxylate superplasticizer of thixotropic cementitious composites influence mechanism.The results show that with the increase of nano-SiO₂ content,the consistency of the newly mixed cement-based composites decreases first and then increases,and the thixotropy increases first and then decreases.With the increase of PVA fiber content,the consistency and thixotropy of the newly mixed cementitious composites increase gradually.With the increase of the content of polycarboxylate superplasticizer,the consistency and thixotropy of the newly mixed cementitious composites decrease gradually.（5）Through the cube compressive strength test,the cube compressive strength of cement-based composite material was measured.The influence of nano-SiO₂,PVA fiber and polycarboxylate superplasticizer on the compressive strength of cementitious composites was analyzed,and the corresponding influence law was obtained,and the influence mechanism of nano-SiO₂,PVA fiber and polycarboxylate superplasticizer on the compressive strength of cementitious composites was revealed.The results show that the cubic compressive strength of c cementitious composites increases first and then decreases with the addition of nano-SiO₂.With the addition of PVA fiber,the cube compressive strength of cementitious composites increases first and then decreases.With the addition of polycarboxylate superplasticizer,the cube compressive strength of cementitious composites decreases gradually.