Study On The Resistance To Chloride Ion Permeability And Mechanism Of Marine Cementitious Materials In Marine Environment

The service life of reinforced concrete structure in marine environment is generally short,and the corrosion of steel bars caused by chloride ion invasion is one of the major causes.As a weak part of concrete,cementitious materials must have good resistance to chloride ion penetration when used in marine engineering.Marine cementitious materials(MCMs)have excellent mechanical properties and chloride penetration resistance,which can be widely used in marine concrete structures.In this paper,the MCMs are prepared by replacing Portland cement with high proportion of mineral slag,basalt powder and desulfurized gypsum,with some ultra-fine active mineral admixtures such as silica fume and fly ash cenosphere added to improve their properties.By studying the effect of each component on the performance of MCMs,the content of MCMs was determined.Moreover,the influence of water binder ratio and curing age was analyzed.According to the results,five components were selected to prepare marine concrete,and its strength and resistance to chloride ion permeability were studied.In addition,the hydration and microstructure were studied by Fourier transform infrared spectroscopy,X-ray diffraction and mercury intrusion porosimetry.The main research works and results are as follows.(1)The effects of mineral slag and basalt powder on MCMs were studied.The results showed that the compressive strength and resistance to chloride ion permeability of MCMs decreased with the increase of mineral slag,and the proper content of basalt powder had little effect on MCMs.When the content of mineral slag was more than 55%and the content of basalt powder was less than 12%,resistance to chloride ion permeability of MCMs was the best.Compared with ordinary portland cement,the chloride diffusion coefficient of MCMs is reduced by about 50% in 28 d,and about 75% in 56 d,meeting the needs of marine engineering.(2)The influence of silica fume and fly ash cenosphere on MCMs was studied.The results showed that with the increase of silica fume,the early strength of MCMs increased and the diffusion coefficient of chloride ion decreased.When 2% of silica fume added,the chloride resistance of MCMs was improved—the chloride diffusion coefficient reduced by50% after 28 days of curing.The fluidity of MCMs mortar decreased with the increase of silica fume,and increased with the increase of fly ash cenosphere content.When adding silica fume,the addition of fly ash cenosphere can improve the fluidity of MCMs mortar.Furthermore,the properties were improved effectively,especially the resistance to chloride ion permeability in the later stage(84d)— the chloride ion diffusion coefficient decreased by about 50%.(3)The effects of curing age and water binder ratio on MCMs were studied.The results showed that due to the secondary hydration of pozzolanic materials,the strength and chloride ion resistance of MCMs continued to increase by about 50% after 28 days of curing.Polycarboxylate superplasticizer improved the fluidity,mechanical properties and durability of MCMs with the water binder ratio of 0.35.(4)Five groups of MCMs were selected to prepare marine concretes,with the strength and chloride penetration resistance studied.The results showed that compared with ordinary concrete,the resistance to chloride ion penetration of marine concrete was better.The resistance to chloride penetration of the HGC2-HGC5 were rated as Q-? at the ages of 28 days and decreased by 50% and 40% at the ages of 56 and 84 days,rated as Q-?.The coulomb electric flux of HGC1 was higher at the ages of 28 days.But its chloride resistance grade was rated as Q-? at the ages of 56 and 84 days,which also meet the needs of marine engineering construction.(5)The hydration of MCMs was studied.The results showed that,due to the pozzolanic effect of the active mineral admixtures,the hydrate in the slurry didn't reduce with low content of cement,so the strength and chloride binding capacity didn't decrease.Besides,the packing density of MCMs can be optimized through particle grading of different particle sizes.At the same time,incorporation of mineral admixtures resulted in asignificant reconstruction of the small capillary pores,Consequently,the pore size distribution was optimized and the chloride resistance was improved effectively.