The Research Of Influence On The Reactive Powder Concrete Mechanical Properties By Nano-Silica

This test design orthogonal experiment by orthogonal table of L₉(3⁴) to chose theoptimum mixture ratio through range and variance analysis. Adding different contents ofnano-SiO₂on the basis of ratio, the regularity of flexural strength, compressive strength,splitting tensile strength, the mixture flow and the size effect of RPC are studied with thenano-SiO₂content and the impact mechanism is analyzed by scanning electron microscopyfrom the microscopic point of view.We can get the following results through testing and data analysis:(1)The impact of the nano-SiO₂content on the mechanical properties and workability ofliquidity of RPCa.When the content of nano-SiO₂is0.5%, the compressive strength, flexural strength andsplitting tensile strength can achieve the maximum value. With the content of nano-SiO₂continue to increase, the intensity value begin to decrease, which can indicate that within acertain range, the nano-SiO₂can improve the compressive strength,the flexural strength andsplitting tensile strength of RPC. With the growth of the age, the flexural strength andsplitting tensile strength values continue to increase, while the compressive strength value hasbeen reduced, indicating that the compressive strength has strength retraction phenomenon.b.With the increase of nano-SiO₂content, the axial compressive strength of RPCincreases and then decreases, the elastic modulus and the peak strain will change with theaxial compressive strength, that is to say they will increase when axial compressive strengthincrease and decrease with the decrease of the axial compressive strength.nano-SiO₂contentdon't have significantly impact on the strength conversion factor and the average is0.841.Inaddition, the lateral deformation coefficient doesn't have obviously change in the law, whichis within the range of0.213to0.221and an average of0.217,indicating that the nano-SiO₂content has no effect on lateral deformation coefficient of RPC basically and its value isdiscrete.c.With the increase of nano-SiO₂content, the RPC mobility first increases and then decreases. When the nano-SiO₂content is0.5%, the fluidity RPC can reach192mm whichimprove4.92%,compared with the reference concrete of N1. But with the increase ofnano-SiO₂content, the fluidity of the concrete began to fall, when the volume is increased to1.5%, the minimum of RPC fluidity is175mm.(2)The impact mechanism of the nano-SiO₂content on RPC performancea.The impact mechanism of the RPC workability: the particle size of nano-SiO₂issmaller than silica fume,they can fill gap each other with silica fume and cement particleswhich make the particle size distribution of hybrid system more reasonableï¼›nano-SiO₂particles shape is approximately spherical and it has "ball effect"ï¼›nano-SiO₂particles size ismuch more small compared to cement particles, so it plays a part of "dispersion effect" whichimprove the flow of RPC.b.The impact mechanism of RPC mechanical properties: nanoparticles have the "surfaceeffect" and the "small size effect", when the particle size is reduced to the nanometer level, itssurface area and surface energy will increase rapidly, and thus its chemical activity andcatalytic activity become very high, it can reaction with the Ca(OH)₂which is early productsof cement hydration reaction, which decrease Ca(OH)₂concentration and speed up theprocess of cement hydrationï¼›nano-SiO₂can also physical fill capillary gap in the concrete, gelvoids and calcium silicate hydrate layer crystallization gap, increasing the density of RPC,and nano-SiO₂in the hydration reaction nuclei, the formation of calcium silicate hydrate gelphase in its particle surface, the loose hydrated calcium silicate gel into a dense networkstructure, improved the structure of the RPC interface, thus improving the early mechanicalproperties of concrete.(3)The impact of the nano-SiO₂content on size effectThe compressive strength of RPC decreases with the increase of test block size,which isthe same as the ordinary concrete and high-performance concrete compressive strength sizeeffect law. Although the content of nano-SiO₂is different, the size effect coefficient of thefive kinds of test block which the side length is70.7mm and40mm do not change obviously,and it doesn't have significant variation. the average of compressive strength conversionfactor of the side length of70.7mm and the cube of side length100mm is0.96,while theaverage of compressive strength conversion factor of the side length of40mm and the cube ofside length100mm is0.93,indicating that the RPC cube compressive strength size effect isvery small compared with ordinary concrete and the size effect is not significant.