The Rheological Properties, Hardening Properties And Micro Properties Of Nano-material Composite Self-compacting Concrete

This thesis systematically studies the effects of different nanomaterials(nano-silica,referred to as NS;nano-calcium carbonate,referred to as NC;graphene oxide,referred to as GO)on the rheological properties,hardening properties and microscopic properties of self-compacting cement-based materials.Rheological properties are important properties of self-compacting cement-based materials and largely determine their hardening properties.In order to reduce the environmental impact of SCC,fly ash(FA)is used instead of cement to reduce the amount of cement,and High Range Water Reducing Admixtures(HRWRA)is combined to ensure the basic working performance of SCC.Therefore,the orthogonal test is used to analyze the rheological parameters,fluidity,flexural strength and compressive strength of nanocomposite self-compacting paste and mortar by influencing factors such as FA content,PCE content and NS/NC/GO content.The strength affects the effect size,and the relationship between the nanocomposite self-compacting paste and the rheological properties of the mortar is obtained.The rheological laws of the composite nano-materials self-compacting cement-based materials are deeply explored,and the relationship between rheological properties and macroscopic properties is clarified..Based on this,according to the performance balance design,the appropriate mix ratio is applied to the nano-composite SCC,and the nano-composite SCC hydration products and microscopic are analyzed by combining various advanced material testing methods(such as XRD,SEM-BSE,MIP and TGA).The structure establishes the logical relationship between the microscopic properties of the slurry and the macroscopic performance of the concrete,and finally forms the nanocomposite SCC design theory of the system.The specific content and conclusions include the following aspects:(1)HRWRA content selected for FA dosage(10-30%),nano material content(NS/NC:1-3%,GO:0.01-0.05%)and self-compacting paste,mortar(NS composite self HRWRA range of dense paste/mortar:0.4-0.8%/0.9-1.9%;HRWRA range of NC composite self-compacting paste/mortar:0.10-0.14%/0.56-0.62%;GO composite self-compacting paste/mortar HRWRA range:0.05-0.07%/0.24-0.36%)Three factors and levels,according to Minitab software analysis,three factors and different dosages of self-compacting paste,mortar rheological parameters(plastic viscosity,Referred to as?;yield stress,referred to as?o),fluidity,flexural and compressive strength of the regression equation and contour map.Taking self-compacting paste as the core and self-compacting mortar as the bond,it is preferred to have a proper mix ratio of?o between 30-70 Pa·s,fluidity between 260-280 mm and compressive strength between 50-70 MPa,and finally The optimal combination ratios selected were 20%FA+2%NS,10%FA+2%NC and 10%FA+0.03%GO,respectively..(2)The three factors have the same effect on the?,?o and fluidity of the nanocomposite self-compacting paste and mortar.The influence of the nanomaterials is relatively large,and the FA content is?,?o among the three factors.And the degree of fluidity is minimal.From the rheological point of view,the shear behavior of the self-compacting paste and mortar of the three nanomaterials is nonlinear.Although the viscosity of self-compacting paste and mortar increases with the incorporation of nano-materials,with the incorporation of FA,it has a favorable effect on the workability of self-compacting paste and mortar,and can reduce the shear thickening degree of the slurry.For NS/NC/GO composite SCC,both?_o and?increase,but the proper amount of HRWRA is incorporated,which avoids the SCC bleeding and aggregate settlement,which improves the working performance,improves the fluidity and improves the passing ability.(3)The SEM and BSE analysis showed that the nano-material promoted the secondary hydration of FA,so that the surface of the FA glass shell was dissolved,the surrounding hydration products increased,and the interface transition zone was more encrypted.Combined with MIP,it can be seen that the harmful pores(0.05-0.2?m)of nanocomposite SCC decreased by 0.6-12%compared with the control group,and the harmful holes(>0.2?m)decreased by up to 23.2-50.8.%,the pore size distribution is optimized.It can be seen from the XRD and TGA analysis that although no new hydration products are produced in the slurry,the surface of the nanomaterial will bond with CH to form more CSH gel and improve the adhesion of the interface transition zone.The reason for the improvement of the strength of nano-self-compacting cement-based composites is effectively explained.From the perspective of flexural and compressive strength,although FA content has an adverse effect on the flexural and compressive strength of self-compacting cement-based materials,it is still positively correlated with the strength under the second-order action of nanomaterials.In addition,according to the mechanical properties of nanocomposite SCC,it can be seen that the synergistic effect of NS/NC/GO and FA can significantly improve the compressive strength in the early and late stages at a certain compounding ratio.The early 3d intensity of nanocomposite SCC is compared with the control.The group increased by 6.4-14.9%;while the 28d compressive strength of nanocomposite SCC increased by 20.6-26.2%compared with the control group,and the compressive strength of 28d reached 50-70MPa.