Experimental Study On Nano-SiO₂-basalt Fiber-CaCl₂ Recycled Concrete

With the rapid development of urbanization in China,the volume of China’s construction industry ranks first in the world,and the environmental pollution caused by the construction waste is also becoming more and more serious.The resource treatment of the urban construction waste has become one of the goals of China’s environmental protection and sustainable development strategy.The main component of construction waste is waste concrete,and the waste concrete can be crushed and screened to meet the particle size requirements of recycled aggregate to make the recycled concrete,which can effectively improve the efficient utilization of construction waste.However,the mechanical properties and durability of the recycled concrete are poor and cannot meet the requirements of the construction industry.To overcome the defects of the recycled concrete,the mechanical properties of recycled concrete can be improved by adding admixtures including nano-SiO₂and basalt fibers.Considering the complementary advantages of nano-SiO₂,basalt fiber and CaCl₂,this paper proposes an admixture with excellent performance to improve the mechanical properties of recycled concrete.The main research contents and results of this paper are as follows:（1）Through the study of the nano-SiO₂,basalt fiber,and CaCl₂with different contents,the suitable raw material ratio is determined,the recycled concrete is prepared by using the optimal raw material ratio,and the influence of recycled concrete on the work ability,mechanical properties,and durability is analyzed.In addition,the XRD and SEM are used to analyze the change in phase composition and micro-morphology of recycled concrete after adding nano-SiO₂and CaCl₂.The mechanical properties of cement sand adding the nano-SiO₂,basalt fiber and CaCl₂are tested by the cement sand compressive and flexural testing machine.（2）The glue-sand and water-to-adhesive ratios of the recycled concrete are determined by the adaptation,and then the effects of the nano-SiO₂,basalt fiber,CaCl₂,and recycled coarse aggregate on the mechanical properties of recycled concrete are explored through orthogonal tests,and the relationships between the nano-SiO₂,basalt fiber,CaCl₂,and recycled coarse aggregate are established by range and variance analysis.（3）The effects of the nano-SiO₂,basalt fiber,and CaCl₂on the durability of recycled concrete are explored,and the freeze-thaw cycle test,chloride ion resistance test and carbonization resistance test of recycled concrete are conducted.The results show that the durability of recycled concrete is improved after adding the nano-SiO₂,basalt fiber and CaCl₂,and the mass loss rate is 3.02%after 300 freeze-thaw cycles.The carbonization depth of 28d is 7.26mm,and the chloride ion mobility coefficient is1.83×10^-12m²/s.