Analysis And Experimental Research On Mechanical Properties And Microstructure Of Nano-SiO₂ Concrete With Basalt Fiber

The basalt fiber concrete with nano-SiO2 as a new type of high performance composite materials has many advantages,such as high strength,high toughness,etc.It has overcomed the disadvantages of common concrete,for its low tensile strength,easily cracking.The experiments of cube compressive strength,splitting tensile strength,flexural strength and microstructure were conducted and the effects of nano-SiO2 and basalt fiber on the mechanical properties were studied,and the mechanism was analysised by the microstructure in paper.The experiments about compressive strength,splitting tensile strength and flexural strength of concrete at 28d age were tested under different content of nano-SiO2 and basalt fiber.Among them,The nano-SiO2 content can be 0%,0.6%,1.2%,1.8%,30%,the basalt fiber content can be Okg/m3,2kg/m3,3kg/m3,4kg/m3,5kg/m3,which were measured by 20 group tests.The test showed that with the nano-SiO2 content increasing,the compressive strength,splitting tensile strength and flexural strength of concrete only adding nano-SiO2 increased and then declined.When the content was 1.2%,the strength was better.The compressive strength,splitting tensile strength and flexural strength of this concrete was respectively 7.07%,6.06%and 15.04%more than that of standard concrete.With the basalt fiber content increasing,the strength of concrete only adding basalt fiber first increased and then declined.Its optimium content was 3kg/m3 the compressive strength,splitting tensile strength,and flexural strength of this concrete was respectively 3.62%,8.71%and 10.70%more than that of standard concrete.For the concrete adding both basalt fiber and nano-SiO2,when the nano-SiO2 content was 1.2%and the basalt fiber content was 3kg/m3,the strength increased obviously.Compressive strength,splitting tensile strength and flexural strength of this concrete was 9.04%,17.42%and 29.60%more than that of standard concrete.The mechanical properties experiments of concrete at 7d age with 1.2%nano-SiO2 and 3kg/m3 basalt fiber were carried out.The test showed that the compressive strength of nano-SiO2 concrete,basalt fiber reinforced concrete,basalt fiber concrete with nano-SiO2 was respectively 17.46%,11.82%,25.67%more than that of standard concrete,splitting tensile strength was respectively 14.07%,17.08%,23.62%and flexural strength was 16.37%,11.74%,27.05%.The results showed the nano-SiO2 was benefical to the early compressive strength and flexural strength of concrete,while the basalt fiber could enhance the early splitting tensile strength and flexural strength of concrete,so it could be included that basalt fiber and nano-SiO2 could work well together which would improve the early strength of concrete obviously.On the foundation of the early basic mechanical properties experiments,the hydration products of concrete were observed by scanning electron microscope.The results indicated that with the increase of nano-SiO2,the amounts of AFt crystals and C-S-H gel increased gradually,the holes and fracture reduced gradually.When the nano-SiO2 content was 1.2%,the amounts of AFt crystals and C-S-H gel were larger,the cement structure was dense.When the basalt fiber content was 3kg/m3,the connection between fiber and matrix was tight and fibers were well dispersed in the gel.Dense spatial structure was formed in the cement stone.The macroscopic mechanical properties agree well with the analytical results about microstructure.