| The durability of concrete directly determines the safety service life of concrete.In recent years,how to enhance the durability of concrete has attracted much attention.Nano-modified concrete provides a very effective and feasible solution to enhance the durability.The durability of concrete is a comprehensive performance.And resistance to chloride ion permeability and frost resistance are two important aspects about the durability.At present,mineral admixtures are widely used in concrete that not only reduce the cost,and also improve the workability and the durability of concrete.However,there are some mineral admixtures,such as slag and fly ash,with slow hydration,large particle size,not sufficient hydration and other adverse aspects.The nano-Si O2 used in this subject is a fine particle with a small size of 7-40 nm.It has high specific surface area,high reactivity and good filling performance.It can make up for the shortcomings of mineral admixtures to a certain extent and get better to improve the effect.Moreover,the activity effect,the filling effect and the nucleus effect of nano-Si O2 can regulate the structure of the gel on the microscopic scale.Refine the grain,reduce the porosity,improve the compactness of the concrete and the macroscopic performance improvement includes the resistance to chloride ion permeability and frost resistance.Therefore,it is very important to study the durability of nano-Si O2 synergizing mineral admixture to improve the durability of concrete and increase the service life of concrete structure.In this paper,we mainly study the effect of nano-Si O2 synergizing slag and fly ash on concrete,including the workability of fresh concrete,the strength of hardened concrete,the resistance to chloride ion penetration and frost resistance.We also analyze the improvement and impact of the appropriate amount of slag,fly ash and nano-Si O2 with the appropriate feeding and mixing methods to prepare the concrete.Based on the study of slump and rheology test,compressive strength analysis,resistance to chloride ion permeation,freeze-thaw cycle,pore structure analysis and scanning electron microscopy analysis of concrete samples,it is proved that nano-Si O2,slag and fly ash can complement each other and improve the workability,mechanical properties and durability of the concrete.The main results are as followings:?1?Using 150 W power ultrasonic dispersion of nano-Si O2,naphthalene powder water reducing agent to adjust the workability and 30 wt% of the amount of fly ash or slag synergies can better disperse nano-Si O2 to maintain a certain degree of slump and get the best concrete strength.?2?With the content of nano-Si O2 increased,the rheology of cement slurry deteriorated and the slump of fresh concrete decreased;when 1 % by weight of nano-Si O2 modified high water-cement ratio of ordinary concrete and 0.8 wt% of nano-Si O2 modified low w/c of high-strength concrete,the influence of the rheological properties is relatively small and fresh concrete slump maintained at 100 mm.The nano-Si O2 continually increased will seriously affect the workability of concrete.?3?Nano-Si O2 and fly ash or slag synergistic modified ordinary concrete's compressive strength has maximum increase of 10 MPa;synergistic modified high-strength concrete's compressive strength has maximum increase of 20 MPa;synergistic modified maximum aggregate diameter 16 mm high strength concrete's early strength is higher than that of the maximum aggregate size of 20 mm,but the later strength of concrete with the maximum aggregate diameter of 20 mm is higher.The strength of nano-Si O2 modified high strength concrete with improved mixing method is higher than that of conventional mixing,the early strength increased by 5 MPa or more and the latter strength increased by 10 MPa or more.?4?The diffusion coefficient of chloride ion with high strength concrete was smaller than that of ordinary concrete.The diffusion coefficient of high strength concrete modified with nano-Si O2 and slag was smallest of 1.12×10-12 m2 / s;the diffusion coefficient of chloride ions with the maximum aggregate size of 16 mm was the smallest of 1.11×10-12 m2 / s,which was 69.59 % lower than that of the blank group.The chloride ion diffusion coefficient of the high strength concrete with the maximum aggregate size of 20 mm is 112×10-12 m2 / s,which is 75.55 % lower than that of the blank group.The high strength concrete modified by nano-Si O2 with improved mixing method has significantly lower diffusion coefficient of chloride ion than that of conventional mixing method.?5?Nano-Si O2 and fly ash or slag synergistic modified ordinary concrete's frost resistance has the best nano-Si O2 content of 1 wt%.At this time,the frost resistance of concrete modified with nano-Si O2 and fly ash has the best increase than the blank group,the increase value is 10.71 %.The highest frost durability index with synergy nano-Si O2 and slag is 46.47 %.The best content of nano-Si O2 for synergistic modified high strength concrete's frost resistance is 0.8 wt%.At this time,the biggest frost durability index of concrete modified by nano-Si O2 and slag is 89.55 %,and increased by 18.34 %.The nano-Si O2 cooperated with fly ash or slag to modify the largest aggregate size 16 mm high strength concrete's frost durability index is generally higher than the maximum particle size of 20 mm,but the frost resistance durability index has the lower improved.With modified by nano-Si O2 and fly ash,the durability index was 89.7 % when using the improved mixing method,whereas the frost durability index of conventional mixing only is 82.67 %;the durability index of concrete modified nano-Si O2 and slag increased from 89.55 % to 95.5 %,compared with conventional mixing method.?6?Because nano-Si O2 has better activity and smaller size than mineral admixtures,it can improve the pore structure of concrete at a more microscopic scale,fill and refine pores.Improved mixing method can make nano-Si O2 better dispersion,which can reduce the defect and the porosity of the interface.The nano-Si O2 also improves the concrete microstructure,consumes the calcium hydroxide and increases the density of the gel. |
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