The Evolution Law And Numerical Simulation Of Pore Solution Ion In Modern Concrete

With the strategy implementation of "One Belt and One Road","Western Development"and "Marine Potestatem",a great deal of infrastructures have been built,and concrete is used widelybecase of its inexpensiveness,wide sources,favourable performance and son on,leading to the rapidgrowth of cement applyment.At the same time,the pollutionproblems and high energy consumption of cement production are worrying.Meeting the needs of development and promoting environmental protection and energy saving,a lot of mineral admixtures are introduce intopreparation of modern concrete,having caused the diversity of raw materials and complexity of cement hydration,and that micro structure and endurancequality of harden concret are different with general concret.The composition,property and change evolvemental law of pore solution in concrte not only concern the hydration degree and reaction rate of various component,species and quantity of hydration production of multivariate gelled material,but also influence mechanical and long-term performance,providing theoretical support for the durability study of modern concrete?Based on the theories of porous media and composite material,the property of pore solution was systematically investigated by experiment and numerical simulation,and traditional test methods and modern analysis techniques were used together in this study.The ion leachingpperty of staple raw material including cement,fly ash,slag and silica fume was researched firstly and the process,feature and law of ion leaching in raw material were studied at a different angle of pure water and saturated Ca(OH)2.Meanwhile,the visual representation of 3D pore structure in modern concrete is realized by using thermovariable alloy as the intrusion medium of concrete hole structure.In addion,the time-dependent deformation of ion concentration and conductivity of pore solution and the changeable feature of pore structure in concrete were investigated by experiment combined with modeling.Several important research results are as follows:(1)property of filtrate in raw material of modern concreteBased on the leaching method,cement,fly ash,slag and silica fume were soaked in pure water and saturated Ca(OH)2respectively,and the species,concrention and conductivity of filtrate and the Zeta potential of suspension were systematically measured.The result shown that the dissolution rate of solid were promoted by saturated Ca(OH)2,leading the increasment of K+,Na+,OH',Ca2+ and SO42-concentration and conductivity in filtrate,but the concentration of SiO44-in fly ash,slag and silica fume was reduced.Meanwhile,the initial Zeta potential of cement and fly ash suspension in saturated Ca(OH)2 were reduced,but that in the slag and silica fume were increased.(2)property of pore solution of modern concreteBease on centrifugation and high pressure extraction,early-age and long-time pore solution of cement-fly ash,cement-slag and cement-silica fume were excrated,having researched the influence from water cement ratio(w/c),species and dosage of admixture on the time-depend law of ion concrention and conductivity of pore solution.Effects of w/c,mineral admixture type and content on the property of pore solution were analysed quantificationally.The result shown that the ion concrention and conductivity of pore solution were lowered when w/cwas 0.4,0.5 and 0.6,and the averages degree of reduced effects were 27.91%,43.68%,65.37%and 19.39%,37.29%,50.58%,respectively.The effects of fly ash,slag and silica fume on the changed law of ion concentation,pH and conductivity were not obvious,but having reduced them.At the same dosage(10wt%)of fly ash,slag or silica fume,ion concentration(K+?Na+?OH-?Ca2+ and SO42-)and conductivity were averagely reduced by 29.42%,38.88%,51.72%and 25.94%,43.89%,46.50%,respectively?(3)Visualization of 3D pore structure in modern concreteA new technique of Nano X-ray CT combined with thermovariable alloy enhancing was created to visually characterize the 3D pore structure in modern concrete(patentNo.201710461648.2).The contrast of CT images was greatly improved and the parameter of pore structure could be acquired exactly,which provided a powerful tool for the visualization of 3D pore structure in modern concrete.With this technique,effects of w/c and curing period on pore structure in cement-based materials were studied systematically.3D pore structure wasreconstructed using Nano X-ray CT,and parameters of pore structure could be acquired,providing theoretical support for pore structure of modern concrete?(4)Ion concentration,pH and conductivity of pore solution in modern concrete:modeling and verificationBase on CEMHYD3D model,the hydration models of cement-fly ash,cement-slag and cement-silica fume had been built using "Monte Carlo random number" and coupling the hydration mechanism of fly ash,slag and silica fume.The simulations of ion concentration and conductivity in modern concrete were achieved according to parameters of solubility product and charge conservation principle,comparing with results of experiment,which provided a new method for quickly acquiring ion concentration,pH and conductivity of pore solution in modern concrete.