Mechanical Properties Test And Microstructure Analysis Of Nano-SiO₂ Concrete With Ultra Fine Fly Ash

Adding nano-SiO₂ into concrete can effectively improve the static mechanical properties of concrete.Ultra fine fly ash instead of cement to not only reduce the amount of cement,energy saving,the use of fly ash by-product,and adding an appropriate amount of ultra fine fly ash concrete can improve many properties of concrete.The two mixed into the concrete can play a complementary effect of good results.In this paper,the compressive strength,splitting tensile strength and flexural strength of concrete with nano-SiO₂ and ultra fine fly ash under different dosages were tested.The SEM test of the two optimum dosage was carried out,and the mechanism of two on concrete was analyzed through strength and microstructure.The basic mechanics test about the compression,splitting and flexural strength test of concrete with different nano-Si O₂ and ultra fine fly ash with the curing age of28d.The nano-SiO₂ content can be 0%,0.6%,0.8%,1.0%,1.2%,1.4%the ultra fine fly ash content can be 0%,15%,20%.The test results show that when the nano-SiO₂ only into the concrete,the compressive strength,splitting tensile strength and flexural strength were increased with the increase of nano-SiO₂ content showed a downward trend after rising concrete,When the content was 0.8%,the compressive and splitting tensile strength and flexural strength increase in the best effect compared with the common concrete,concrete were increased by 22.5%,16.94%,13.70%.Concrete mixed with ultra-fine fly ash,compared with the optimal content of 20%of the dosage of 15%,At this time,the compressive strength,splitting tensile and bending strength of concrete were increased by 12.8%,6.56%,and 5.94%,respectively,compared with the common concrete specimens.When nano-Si O₂ and ultra-fine fly ash were mixed in concrete,when nano-Si O₂ content was 1.0%and ultra fine fly ash content was 15%,the increase effect of compressive strength,splitting tensile strength and flexural strength is the best,which was increased by 21.9%,16.21%and 13.18%respectively compared with common concrete specimens.The compressive and splitting tensile tests were carried out with 1.0%nano-SiO₂and 15%ultra fine fly ash mixed in concrete at curing ages of 3d,7d and 14d respectively.The experimental results show that adding nano-SiO₂ can improve the compressive strength and splitting tensile strength of concrete at different ages,adding ultra-fine fly ash reduces the compressive strength and splitting tensile strength of concrete at 3d and 7d.The nano-SiO₂ and ultra-fine fly ash complex doping both improve the compressive strength and splitting tensile strength of concrete at different ages,and the enhancement effect is better than single doped nano-Si O₂.It can be seen in concrete admixture of nano-SiO₂ and ultra-fine fly ash,can significantly improve the early mechanical properties of concrete.Based on the static mechanical properties of nano-SiO₂ ultra fine fly ash concrete,micro-scanning electron microscopy?SEM?tests were carried out on nano-Si O₂ ultra fine fly ash concrete with curing ages of 7d and 28d.The results show that when the concrete is doped with 1.0%nano-SiO₂,the internal structure of the concrete is more compact than common concrete of the same age.When the concrete incorporates 15%ultrafine fly ash,the internal structure of 7d is less dense than ordinary concrete of the same age.When the two are mixed into concrete,a large number of regular AFt crystals and amorphous C-S-H gel were overlapped with each other to form a relatively dense network skeleton system,The holes and cracks in the internal structure of the concrete were effectively filled,the density was significantly enhanced.