| Previors research has proved that Nano-Titanium oxide (NT) can not only endow cement-based materials with photocatalysis, self-cleaning and other functional properties, but also improve the mechanical properties (e.g, strength, toughness, fatigue and creep) and electrical properties. As one of the important achievements in the field of new type of building materials in the 1990s, Reactive Powder Concrete (RPC) has high strength and toughness. Considering the improvements of NT to cement-based materials and its functionality, different crystal phases and particle sizes of NT have been mixed with RPC replaced the mass of cement to develop RPC containing NT with superior mechanical and electrical properties. The effect and its mechanisms of the composition and size of NT on RPC are investigated based on mechanical properties, electrical properties and microstructure of RPC with anatase titanium NT(10nm and 15nm), rutile titanium NT(50nm,500nm and 1500nm) and special types of NT(NT coated by SiO2 and mixed NT). Main contents are as follows:(1) NT is difficult to disperse in cement-based materials. In addition, current researches mainly focuse on effects of NT on cement paste and cement mortar.However, studies of high performance concrete with NT are quiet few. Both mechanical mixing and super plasticizer are used to enhance the dispersion of NT in RPC. In order to get RPC containing NT with good workability and stable performance, workability of RPC with different NT contents is adjusted by changing the content of super plasticizer.(2) Mechanical properties and electrical properties of RPC with 10nm and 15nm anatase titanium NT are tested and the microstructure of RPC with anatase titanium NT is observed by scanning electron microscopy (SEM). And then the effect of NT on the performance of RPC is analyzed. Research results indicate that of anatase titanium NT with different particle sizes has different effects on the performance of RPC because of the difference of nucleation rate. Two kinds of NT can improve the late compressive strength and splitting tensile strength of RPC, and 10nm anatase titanium NT has better effects. Two kinds of NT can decrease the resistivity of RPC, and 15nm anatase titanium NT has better effect. Due to NT particles with high specific surface area which will adsorb water so that the cement hydration is not complete at the late stage, two kinds of NT can weaken the late flexural strength of RPC.(3) RPC with 50 nm,500 nm and 1500 nm particle size of rutile titanium NT are prepared, and their flexural strength, compressive strength, splitting tensile strength and resistivity are tested. Besides, the effect mechanisms of NT to RPC performance are discussed by using scanning electron microscope. Research results indicate that rutile titanium NT has better effects than anatase titanium NT on the overall performance improvements of RPC.This is because rutile titanium NT is more stable due to its dense lattice structure and has more effective filling effect due to its large particle size. In addition, rutile titanium NT with different particle sizes has different effects on the performances of RPC. All NT can improve the late compressive strength and splitting tensile strength of RPC, and 500nm rutile titanium NT has optimal effect. For the late flexural strength, the larger NT particle size is, the better its improvement effect will be. The addition of 50nm rutile titanium NT lower the strength of RPC. All rutile titanium NT with different particle sizes can decrease the resistivity of RPC, and 500nm rutile titanium NT has best effect.(4) In addition to anatase titanium NT and rutile titanium NT, two kinds of special NT are selected:RPC with rutile titanium NT coated by SiO2 and mixed NT of anatase titanium NT and rutile titanium NT. The effects and mechanisms of these two kinds of NT on the performances of RPC are studied through flexural strength test, compressive strength test, resistance test and SEM observision. Research results indicate that NT coated by SiO2 has best improvement effect on the strength of RPC compared with other NT in this paper. Because this type of NT occurs pozzolanic reaction with RPC, and more dense C-S-H gel will be generated while CH crystal will decrease. Besides, both special types of NT can decrease the resistivity of RPC, but their improvement effects are less than anatase titanium NT and rutile titanium NT. |
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