Research On Durability Of High Strength Concrete With High-ratio Admixtures And Frost-resistance Of Flexural Beams

The high-strength concrete with its advantages as high strength,good durability and less deformation,etc is suitable for the high-rise,long-span and heavy-load modern engineering structure development,which shall be widely used in the works.The crisis of concrete durability has increasingly emerged.With respect to the harbor in cold area and adjacent buildings,there is peeling off,corrosion and so on in structure surface due to the dual action from freeze thawing and chlorine erosion,which has affected the long term use and safety operation.Therefore,this paper studies the effect that admixture on high strength concrete performance and freeze thawing characteristic of high strength concrete flexural beams under chlorine salt environment through admixtures to provide the basis for engineering application.The main content studied and conclusion as follows:(1)Fly ash and slag shall be used as admixture in which 40% or 50% of total amount will supersede cement to prepare high strength concrete.The scanning electron microscope and X-ray diffraction were used to study the hydration products and degree of concrete under different age.The effects of microstructure change on macroscopic strength were analyzed.The results show that compared with ordinary concrete,the early age compressive strength of concrete with admixtures is low,slag begun to hydration at 7 days and fly ash only have the effect of filler in the early.But its long aged strength increases rapidly,can reach 2-5 times.The strength of concrete with admixtures is higher than the concrete with single admixture.Microstructure test shows that mixing fly ash and slag can promote the secondary hydration of concrete,also produce more hydration products.(2)Research on freezing resistance and chlorine ion permeability of high strength concrete with different admixture amount and mixing ratio shall be carried out through rapid freeze-thaw test and electric flux test.Furthermore,the ratio of frost resistance durability coefficient and electric flux shall be used to evaluate the durability of high strength concrete.The results show that capability to resist chloride ion permeation improved as the increase of fly ash and the decrease of slag in concrete with a fixed share of total mineral admixture.But the increase of total mineral admixture would undermine the capability of concrete to resist chloride ion permeation.The ratio of frost-resistant durability coefficient to electric flux value could effectively evaluate the durability of high strength concrete with high ratio admixture,and we proposed the proper mixing proportion was 50% for admixture amount and the content ratio of fly ash to slag was 4:1.(3)Improve the existing cellular automation model simulating chloride ion erosion procedure and establish cellar automation model simulating chloride ion erosion procedure to admixture concrete by introducing mineral admixture.Moreover,program compiled by Matlab shall be used to carry out numerical simulation for chloride ion erosion procedure to admixture concrete.The results showed that under the long-term exposure,the simulation outcomes using the cellular automata-based model agreed with the practical outcomes in previous studies,and it is reasonable and feasible to simulate the chloride ion diffusion process based on this model.Meanwhile,the model is more suitable for simulation the chloride ion diffusion process of concrete under long age.(4)The high strength concrete flexural beams(120mm×200mm×1200mm)shall be used for freeze thaw experiment under chloride salt circumstance.Non-destructive testing method is to test the thickness of destructive layer and strength of concrete.The ultimate bearing capacity of flexural beams after 300 cycles of freezing and thawing is examined.The results showed that freeze-thaw damage of flexural beams is produce and develop tiny cracks.After 300 cycles of freezing and thawing,the ultimate bearing capacity and strength of concrete are decreases,the thickness of destructive layer continually increases.This paper establish the relation between recycle time of freeze thaw and change from flexural beams destructive layer thickness and concrete strength.