Effect Of Micro-silica And Nano-silica On Mechanical Properties Of Recycled Aggregate Concrete

The implementation of green building concepts and sustainable development policies has made the construction industry more and more concerned about the application of recycled concrete.Recycled aggregates are difficult to be promoted and applied due to various defects.Therefore,scholars have carried out a lot of research and exploration to improve the performance of recycled concrete.As an important substance for material modification,admixtures have been used to improve the performance of concrete.The special properties of silica fume and nano-silica can improve the mechanical properties of concrete.However,recycled concrete is still difficult to apply to building structures after being modified.Mixing silica fume and nano-silica to modify recycled concrete can further improve the performance of recycled concrete,which can fully reflect the advantages of silica fume and nano-silica.At present,there are relatively few studies on recycled concrete mixed with silica fume and nano-silica.This research takes recycled concrete as the object,and makes an in-depth study on the influence of silica fume and nano-silica on recycled concrete,which can be used as a reference and will help to improve the research in this field and further promote its promotion and application.In this experiment,486 cube specimens and 45 cylinder specimens were produced to explore the influence of the mechanical properties and microscopic properties of recycled concrete.Meanwhile,the recycled coarse aggregate replacement rate(RCA rate),silica fume content(MS content),nano-silica content(NS content),and curing age were used as research variables to study recycled concrete.(1)In order to analyze the law of compressive strength and tensile strength of recycled concrete with different RCA rate(0%,50%,100%),MS content(0%,3%,6%,9%)and NS content(0%,1%,2%,3%)at different curing ages(3d,7d,28d),the compressive strength test and tensile strength test have been carried out.The results show that both silica fume and nanosilica can increase the strength of recycled concrete.(2)In order to analyze the law of the failure mode,stress-strain curve,elastic modulus and Poisson’s ratio of recycled concrete with different RCA rate(0%,50%,100%),MS content(0%,3%,6%,9%)and NS content(0%,1%,2%,3%),the test of elastic modulus have been carried out.The results show that nano-silica and silica fume can inhibit the development of cracks,but the effect of improving stiffness and deformability is not obvious.(3)In order to observe the morphological characteristics of recycled concrete with different NS content and MS content from the micro level and analyze the influence mechanism of silica fume and nano-silica on the properties of recycled concrete,the scanning electron microscope experiment(SEM)has been carried out.The results show that silica fume and nano-silica can greatly improve the performance of the transition zone interface.