Nano-SiO₂ Modified High Strength Self-compacting Cement Concrete Pavement Material And Its Performance

As a new type of technical pavement,high strength self-compacting concrete pavement have excellent fluidity.Compared with ordinary concrete pavement,it can not only improve the ability of road surface to resist traffic load,but also save a lot of human resources.Thus,the overall efficiency of concrete construction is improved,the project cost is reduced,and providing a new solution for heavy traffic.In this paper,nano-SiO2 was used to modify the traditional cement-based cement system doped with silica fume and fly ash,and the high strength self-compacting concrete pavement material modified by nano-SiO2 was prepared.First of all,the proportion of each component of cementitious material was determined by orthogonal experiment.On this basis,the compounding ratio of high strength self-compacting concrete was determined.The modification mechanism of nano-sized SiO2 in self-compacting paste was discussed through microcosmic test.Secondly,the anti-freezing and dry-shrinkage properties of self－compacting concrete were studied.Finally,the road performance of high strength self－compacting concrete was evaluated by fatigue test and wear resistance test.The results were as follows:(1)Through orthogonal test,nano-SiO2,silica fume and fly ash were selected as three influencing factors.The order of influence of compressive strength of cement paste on 28d compressive strength was:SiO2>silica fume>fly ash,and the order of fluidity effect was SiO2>fly ash>silica fume.The cementitious material mixture ratio was determined as follows:nanometer SiO2:silica fume:fly ash:cement 1:8:20:71;(2)The mechanical properties test and slump test of concrete showed that with the increase of cement content in 500-700kg/m3,the fluidity of concrete improved gradually,while the compressive strength and flexural tensile strength increased first and then decrease.The strength of cement material was the highest in 650kg/m3.In order to prevent the self-compacting concrete pavement from being too fluidity,and considered the setting of cross-slope,so the cement material was determined to be 600kg/m3;(3)According to the microscopic test,it was found that the incorporation of nano-SiO2 can better enrich silica fume and form a ternary gradation structure around fly ash,thus increasing the compactness of concrete and improving the efficiency of the secondary hydration reaction of the whole cement paste.The hydration reaction rate was increased and the strength of cement stone was increased;(4)The long-term performance of high strength self-compacting concrete was evaluated by combining the freezing resistance test and dry shrinkage test.It was found that the addition of nano-SiO2 could improve the frost resistance of concrete,and the freezing resistance of concrete was the best when the dosage of nano-SiO2 was 1%.However,the dry shrinkage rate increased with the increase of nano-scale SiO2 incorporation,which indicated that nano-SiO2 has a negative effect on the dry shrinkage performance;(5)The pavement performance of high strength self-compacting concrete were studied by fatigue test and wear resistance test.It was found that the incorporation of nano-SiO2 could improve the fatigue performance of concrete.However,the wear resistance increased first and then decreased with the incorporation of nano-sized SiO2,and when the content was 1%,the wear resistance was the best.