Study On The Influence Of Silica Fume And Gneiss Powder On The Mechanical Properties And Frost Resistence Of Concrete

As a natural material,rock has a wide range of distribution and low production and processing costs,which has great research and application value.In the process of mining and processing stone,a large number of waste such as rock powder will be produced,including gneiss powder.These waste stone powder can not be used effectively and reasonably,which not only wastes resources,but also pollutes the local environment.Some studies have shown that the properties of concrete can be improved by mixing silica fume and mineral admixture silica fume.Therefore,mixing silica fume and gneiss stone powder into concrete can effectively utilize the waste gneiss stone powder resources.In this paper,through physical experiments,the orthogonal mixing of gneiss stone powder and silica fume at 10%,15%and 20%and 0%,5%,8%and 10%respectively is systematically studied to replace cement.The influence law of different contents of the two admixtures on the mechanical and frost resistance of concrete is analyzed,and the optimal content of silica fume and gneiss stone powder is determined;The microstructure of concrete was observed by scanning electron microscope,and the influence mechanism of silica fume and gneiss powder on the mechanical and frost resistance of concrete was analyzed,which provided theoretical basis for practical engineering application.The research contents and results are as follows.In order to effectively use the waste gneiss stone powder resources in water conservancy and construction projects,some studies show that the composite of stone powder and mineral admixture silica fume can improve the performance of concrete.Therefore,the silica fume and gneiss stone powder are mixed.The macro physical test method is used to systematically study the influence of different dosage on the mechanical properties and freeze-thaw resistance of concrete when the content of gneiss powder is 10%,15%,20%and the content of silica fume is 0,5%,8%,10%.The optimum content of silica fume and gneiss stone powder is found.The micro structure of concrete is observed by scanning electron microscope In order to provide theoretical basis for practical engineering application,the structure and mechanism of the structure were analyzed.The research contents and results are as follows.(1)The mechanical properties of silica fume and gneiss powder with different content were tested to study the influence of different content of admixture on compressive strength,splitting tensile strength and flexural strength of concrete.The results show that:when the content of gneiss stone powder is less than 15%,it has a weak negative effect on the mechanical properties of concrete;when the content of stone powder is more than 15%,it is very unfavorable to the development of the mechanical properties of concrete;after the composite of stone powder and silica fume,it significantly improves the strength of concrete,which shows that silica fume plays a positive role and has obvious effect,and within a certain range,the strength increases with the increase of silica fume content When the content of silica fume is 8%,the effect is the best.(2)The frost resistance tests of silica fume and gneiss stone powder with different contents were carried out to analyze the mass loss rate and relative dynamic modulus of elasticity of concrete with different contents of admixtures.The results show that:with the increase of freeze-thaw times,the appearance damage of all concrete specimens is more and more serious,the mass loss rate first decreases and then increases,and the dynamic modulus of elasticity continues to decline;when the content of rock powder is 10%,the frost resistance of concrete is improved to a small extent,and with the increase of the content of rock powder,the frost resistance is getting worse and worse.Silica fume has a positive effect on the frost resistance of concrete,and it increases with the increase of silica fume content in the range of 8%,and decreases slightly when the silica fume content is more than 8%.When the silica fume content is 8%,the improvement effect is the best.(3)The comprehensive test results show that the group with the best mechanical properties is p10s8,and the group with the best frost resistance is P10S8.(4)SEM was used to observe the microstructure of different groups of concrete.The results show that gneiss powder mainly plays the role of filling skeleton.When the content is small,it can fill the structural pores and improve the structural compactness;when the content is too large,it will reduce the content of hydration cementitious materials and reduce the performance of materials.When the stone powder and silica fume are mixed together,silica fume can generate more C-S-H gel by promoting hydration of cement,which will increase the density of the inner micro structure and improve the macroscopic properties.