Experimental Research On Performance Of High Performance Concrete Mixed With Metakaolin

With the continuous development of social economy,contemporary buildings have also put forward higher requirements for concrete materials,and ultra-high performance concrete has become one of the main materials for building structures.High performance concrete(HPC),as a new type of building material with high strength and high performance,has received widespread attention.At present,the development of new mineral admixtures for HPC is still an important research direction.The research on the preparation technology and performance of HPC with metakaolin was carried out in this thesis.And the influence of different mass of metakaolin on the mechanical properties of HPC was studied.Secondly,it was focused on the influence of different mass of metakaolin on the resistance to sulfate and chloride corrosion.Based on SEM,XRD microscopic methods,the enhancement mechanism of metakaolin on the strength and durability of HPC was preliminarily discussed.The main conclusions are as follows.(1)The effect of metakaolin on the mechanical properties of cement mortar under different finenesses and different dosages was studied through the cementitous mortar test.The results show that the activity of 10μm(1250 mesh)average particle size metakaolin was equivalent to silica fume,and the metakaolin dosage is 10%of the total amount of cementitious materials,which is basically the same as the range of silica fume.Therefore,the total content of metakaolin and silica fume in HPC was determined 10%in this thesis.(2)HPC was prepared with different ratios of metakaolin to silica fume,and the influence of different ratios on the mechanical properties of HPC was studied.The test results indicate that the optimal ratio of metakaolin and silica fume was 7:3 creating the best comprehensive mechanical properties of HPC including compressive strength,flexural strength and tensile strength.According to the SEM analysis,the optimal ratio of metakaolin to silica fume leading to a reasonable particle gradation of cement,fly ash,metakaolin and silica fume,which makes the most densely packed state of HPC system.Besides,a variety of mineral admixtures can give full play to the size effect,to reduce the porosity of HPC,optimize the pore structure,consume Ca(OH)2,generate a large amount of C-S-H gel,hydrated calcium sulfoaluminate and hydration calcium aluminate and improves the strength of the HPC matrix effectively.(3)The influence of different content of metakaolin on the anti-sulphate erosion performance of HPC was studied using dry-wet cycle anti-sulphate erosion test.The compressive strength corrosion resistance coefficient of HPC concrete specimens mixed with metakaolin are higher than that was 97%of the HPC with 10%silica fume.indicating that the incorporation of metakaolin can effectively improve the resistance to sulfate erosion of HPC.This is because of the combination of metakaolin and silica fume optimize the compactness of the HPC structure,and effectively reduce the content of Ca(OH)2 in HPC.(4)The influence of different mass of metakaolin on the anti-chloride permeability of HPC was studied by the electric flux method,Whether the Friedel salt phase(F salt)was generated in HPC specimens by XRD to analyze the effect of metakaolin on chloride binding.The results found that the total electric flux of HPC specimens were lower than 200C,and the electric flux was the lowest of the specimen with metakaolin to silica fume 7:3,indicating the chloride permeability of the HPC specimen having the best anti-permeability performance.From the XRD pattern the F salt was produced in each HPC samples,the characteristic peak of F salt in the specimen with more metakaolin content is stronger,indicating that the incorporation of metakaolin can promote the production of F salt and increase the chloride bingding of HPC.