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Research on Chemical-mechanical Coupling Effect and Salt Precipitation Characteristics of Porous Storage Salt Aggregate in Asphalt Pavement

Author: ZhaoXiaoHua
Tutor: ZhangXieDong
School: Wuhan University of Technology
Course: Road and Railway Engineering
Keywords: porous storage salt aggregate anticoagulation ice performance molecular dynamics microcosmic mechanism chemical-mechanicalcoupling effect
CLC: U416.217
Type: PhD thesis
Year: 2012
Downloads: 93
Quote: 0
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Abstract


It is wet and rainy in winter on the plateau mountain of China’s Yunnan-Guizhou-Sichuan area, which is easy to form "frozen rain". The road will generate road condensate ice at a low temperature and the pavement skid resistance will be dropped significantly, easily creating vicious traffic accidents. The traditional ways to restrain road condensate ice and get rid of the snow and ice are mainly manual work and sprinkle salt, which is unfavorable in deicing and environmental protection and not applicable for clearing the road condensate ice. A new technology of active anticoagulation ice road--porous storage salt aggregate technology is studied in this paper. The feasibility of salt precipitation in porous storage salt aggregate is firstly studied by using Chemical Kinetic Theory, and then the preparation technology of porous storage salt aggregate, anticoagulation ice performance, anticoagulant ice effect of asphalt storage salt seal, the pavement performance and anticoagulation ice effect of asphalt mixture containing anticoagulation ice filler are studied through laboratory experiments. By using the material Studio materials simulation software, the micro-mechanism which the porous storage salt aggregate dissolve out salt to drop the freezing point and salt sorption-diffusion has been analyzed. Finally based on the law of mass diffusion, the chemical and mechanical coupling effect of the porous storage salt aggregate is studied.The study mainly includes the following aspects:(1) Through the application of chemical kinetic molecular collision theory, the paper studies collision dynamics process of the storage salt aggregate internal salt ion, the anticoagulation ice collision energy, the storage salt molecular inelastic collision energy conversion and the chlorine ion dissociation process during storage salt component collision. The acting mechanism of the porous storage salt aggregate to precipitate salt anticoagulant ice is analyzed. All of that provide qualitative feasibility conclusion for indoor preparation test of the porous storage salt aggregate.(2) The preparation technology, the salt absorption characteristics, the characteristic of continuous release of salting-out agent and compressive strength of the porous storage salt foamed cement pastes have been studied. Their aggregates, including the type, the way, the amount and the mixture ratio range of adulteration with salt, have been determined. The storage salt foamed cement pastes have been filtered into bituminous seal for the test of the anticoagulation ice. The mixing design of porous asphalt mixture containing storage salt filler has been studied, and the pavement performance and anticoagulant ice properties of the storage salt filler asphalt mixture have also been tested. The new porous storage salt foamed cement pastes aggregate which is prepared indoor has good precipitation of salt, and has a good anticoagulant ice effect at the temperature of-5℃.(3) The condensate ice mechanism and condensation process of liquid water have been studied in the use of MS Materials Calculation Software, which show that the reticular ice six-ring water molecules in dense configuration are formed by interconnecting hydrogen bonding of water molecules in the low temperature, and it will penetrate to the entire three-dimensional space of the system until all of the liquid water molecules are frozen.(4) The ice-salt solution coexisting system has been constructed to study microscopic mechanism of salt to reduce the condensate freezing point. Salt can reduce the freezing point of liquid water because that water-water hydrogen bonds have been greatly reduced around the salt chloride ion at the same time that water-chloride ion-hydrogen bonding structure has been formed, and the distance and angle of molecular have been changed. The chlorine ion broken inherent water ice structure in the coexistence and slow the dynamic formation of hydrogen bond structure.(5) The dynamic acting process of salt adsorption and diffusion within the porous storage salt foamed cement pastes aggregates has been simulated by using MS materials simulated calculation software, and the microscopic acting mechanism of the continuous migration and diffusion of Salt is also studied. The essence is the equilibrium process of energy continuous conversion. The correlation of temperature and pressure of salt adsorption and diffusion within the aggregate has been gained. The chloride ion of salt will be absorbed to the surface and internal part of storage salt carrier, and the salt adsorption and diffusion will be influenced greatly by temperature and pressure, especially the adsorption capacity and diffusion of chloride ion are stronger in high temperatures. (6) From the micro-angle of macro-areas, the paper studies salt diffusion characteristics of porous storage salt aggregate based on mass diffusion law as well as chemical-mechanical coupling effect within the structure cased by chemical damage due to the diffusion of salt ions. The essence of the mechanical-chemical interactions of porous media is exactly the equilibrium process of energy conversion between physical and chemical energy. Then, the diffusion equations of chloride ion and sodium ions in the porous storage salt aggregate are proposed in the paper. At last, the mathematical relationships of mechanical injury caused by the dissipation of calcium ions is studied, and the constitutive mathematical relationships of the complex coupling effect between the chemical injury-mechanical damage of the porous storage salt aggregate are built at the preliminary step.The porous storage salt anticoagulation ice materials are the objects of study in this paper. The best mixing design of porous storage salt foamed cement pastes aggregates is gained according to the conclusions from indoor test, and has a good anticoagulant ice effect at the temperature of-5℃which could be used in the early period anticoagulant ice; the mixing design of porous storage salt filler asphalt mixture, the pavement performance and anticoagulant ice properties have been studied, which shows a good precipitate salt property and a good anticoagulant ice effect when the temperature between-4℃and0℃; the microscopic acting mechanism of the continuous migration and diffusion of storage salt and anticoagulation ice properties have been studied, the salt adsorption and diffusion will be influenced greatly by temperature, pressure and concentration, the salt ion broken inherent water ice structure in the coexistence and slow the dynamic formation of ice crystal structure which decrease the condensate freezing point effectively; the diffuse equation of storage salt aggregate have been established from the chemical and mechanical coupling effect of the porous storage salt aggregate, and the constitutive mathematical relationships of the complex coupling effect between the chemical injury-mechanical damage of the salt ion diffuse are built at the preliminary step.The study conclusions of this paper have great theoretical guiding significance and practical application value for the development and expansion application of subsequent new anticoagulation ice material, the establishment of storage salt pavement technical design theory, the establishment of anticoagulation ice performance evaluation system, the exploration of anti-icing essential mechanism for storage salt material and the improvement of chemical-mechanical damage constitutive model of storage salt and anticoagulation ice materials, etc.

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CLC: > Transportation > Road transport > Road works > Roadbed, pavement engineering > Pavement Engineering > Road : use of the material points > Asphalt Pavement
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