Research On Rheological Properties And Stability Of Nano-SiO₂ Modified Self-compacting Concrete

Self-compacting concrete（SCC）has high fluidity and can fill the formwork under the action of its own gravity.However,it is a multi-phase-component material,and the ability to resist such separation occurs under the action of gravity or external forces is defined as stability.In order to improve the flow filling capacity,the stability of self-compacting concrete will be poor.Therefore,nano-SiO₂ is considered to be introduced into SCC to improve its stability and strength,and manufactured sand is introduced to reduce costs and promote environmental protection.In this paper,the rheological properties of SCC equivalent mortar,the rheological properties and the stability of nano-SiO₂ modified self-compacting concrete（NSSCC）were studied.The main research contents are as follows:（1）Influence of nano-SiO₂ on the rheological properties of self-compacting concrete equivalent mortar（CEM）.The rheological parameters of nano-SiO₂ modified cement paste were tested by shear rate-controlled protocol,and the stability of the paste was characterized by the linear viscoelastic region（LVER）was tested by the small amplitude oscillatory shear program.CEM is used to investigate the rheological properties of mortar prepared by manufactured sand instead of natural sand,and nano-SiO₂ is used to adjust the rheological properties.The results show that nano-SiO₂ can improve the yield stress and plastic viscosity,also increase the length of LVER and elastic modulus,thus improve the stability of paste.The mortar which is easy to segregate and bleed water is prepared by replacing natural river sand with limestone manufactured sand.Nano-SiO₂ can avoid segregation and bleeding,while improving strength.（2）Study on the rheological properties of NSSCC.After the nano-SiO₂ was added into the self-compacting concrete,the rheological and workability changes of NSSCC were investigated by changing the water-binder ratio,superplasticizer,manufactured sand content and stone powder content.ICAR concrete rheometer was used to test the rheological parameters of freshly mixed concrete.Slump flow diameter,T500 time and V-funnel flow time were also tested.Combined with the results of compressive strength,the optimal mixture ratio parameters were indicated.The results show that when the nano-SiO₂ content is less than0.3%,the plastic viscosity will be improved with the increase of nano-SiO₂,and the yield stress has little change.The yield stress increases obviously and the plastic viscosity increases slowly when the nano-SiO₂ exceeds 0.3%.The best content of manufactured sand instead of river sand is 20%,and the best working and mechanical properties can be obtained with 5%stone powder content.（3）Stability study of NSSCC.The vibration stability of NSSCC was tested by the vibration segregation rate jump table experiment（VSR）,and the appearance casting stability（ASI）and static stability（SI）of NSSCC cube column were evaluated by image analysis method.The results show that nano-SiO₂ can reduce the VSR of SCC,but affect the ASI.An appropriate amount of nano-SiO₂ can reduce the SI,that is,improve the stability of self-compacting concrete.