| Rich-water packing material is paid much attention due to its high water-solid ratio,good fluidity and low cost.Meanwhile,the promotion and application of rich-water packing material are affected by poor stability because of high water-solid ratio.Since a large number of ettringite crystals and unbound water exist in the hardening body,the equilibrium condition of filling body would change under the load.This will lead to the instability and disruption of packing hardening body.In order to investigate the relationship of rich-water packing material stability with time and water-solid ratio,as well as the failure characteristics and critical conditions of rich-water packing material under load.This thesis focuses on the study of creep behavior and the change of microstructure characteristics of rich-water packing material with different water-solid ratios in different stress conditions.A creep damage model for rich-water packing material is built.The deformation characteristics,water migration and the relationship of macro mechanics of hardening body in the creep process are analyzed.The critical water-solid ratio of filling body in the stable creep stage and the long-term stability conditions of filling body are proposed.In addition,the study reveals the failure deterioration mechanism from the view of unbound water and studies on the modification of rich-water packing material.In this work,rich-water packing material with different water-solid ratios is manufactured and its basic properties are tested.Its mechanical properties and failure characteristics are studied by using creep and uniaxial compression tests.Creep damage model is established by introducing damage variable.Filling body microstructure and failure deterioration mechanism are analyzed by the means of X ray diffraction(XRD),Scanning Electron Microscope(SEM),Differential Thermal Analysis-Thermal Gravimetric(DTA-TG)and unbound water test.In order to improve the rich-water packing material performance,the single cementitious system is changed into binary ones to prepare a rich-water packing material with better properties.The performances of modified material are studied by means of mechanics and microscopic tests.The main contents and conclusions are summerized:(1)There are main ettringite and a small amount of aluminum in the rich-water packing material.Ettringite crosses each other in shape of needle-like or thin rod-like clusters,which can form a network structure.The network structure has a lot of voids that can fill large amounts of unbound water.(2)The rheological properties and strength of rich-water packing material are related to the stress and water-solid ratio.Gel time gets longer with the increase of water-solid ratio.The strength reduces with the increase of water-solid ratio.The stress-strain curve shows four stages,i.e.,initial deformation,elastic,plastic deformation and disruption.The smaller the water-solid ratio is,the larger the peak stress will be.Elastic modulus decreases with the increase of water-solid ratio.The creep curve of rich-water packing material has decayed stage and steady stage when the stress level is low.The acceleration stage appears in the creep process when the stress level reaches a critical value.The critical loads of filling body with water-solid ratios of 1.7,2.0 and 2.5 are 92%,90%and 85%of their compressive strengths,respectively.Critical load decreases with the increase of water-solid ratio.The larger the water-solid ratio,the larger the strain of creep under the same stress level.The rich-water packing material with water-solid ratio 2.5 gives rise to on crack earlier and faster failure.(3)The creep damage model and constitutive equation for rich-water packing material are established.The equation of deformation modulus varing with stress and time is deduced based on creep test data.The damage evolution equation is built by introducing damage variable.The damage variable is brought in Burgers model.The creep damage model and constitutive equation are established.The model and equation consider the influence of time and stress on creep parameters,that can reflect the weakening of parameters over time and the damage deterioration law of rich-water packing material.According to the test data,the parameters are inverted and the curves are fitted.By comparing with the test curves,the model shows that the damage deterioration law of rich-water packing material can be described before the failure.(4)The creep damage and deterioration mechanism of rich-water packingmaterial are discussed.Creep causes the ettringite crystals to break and form cracks.The cracks expand into large cracks with the increasing of stress.The content of combined water is almost the same as that before and after creep.Creep does not affect the combined water content.The relative loss of unbound water shows linearly positively correlated with the loading level.The slope of the fitted straight line becomes large with the increase of water-solid ratio.The larger the water-solid ratio,the more likely it is to loss unbound water.The migration and loss of unbound water is an important reason for the failure of rich-water packing material.When subjected to the load,the original equilibrium condition changes resulting in the migration of unbound water.The unbound water runs in the cracks and seeps out of the surface of rich-water packing material with the increase of the load,resulting in structure loose and more cracks in hardening body,and large deformation under the load.The filling body will fail when the unbound water loss exceeds the critical value.(5)Put forward the technical scheme of improving the rich-water packing material and obtain excellent performance.The gel time is shortened.The quantity of ettringite is increased and the size of it is reduced.The porosity of hardening body is decreased and cohesive structure is more compact.The strength is improved and the development of late periode strength is stable,which can overcome the late periode strength development defect of the singal cementitious system.The peak stress of the stress-strain curve is increased and the elastic modulus becomes large.The critical load of failure is raised and the deformation becomes small.The strain of creep is decreased under the same stress.The bearing capacity of filling body is improved and the settlement is decreased.The loading range of filling body in the stable creep stage is enlarged.The relative loss of unbound water shows linearly positively correlated with the loading level and the slope becomes small.The unbound water loss is lower than that before modification when filling body is failed.(6)The water-solid ratio application scope of rich-water packing material is proposed.Taking into account the performance indexes of rich-water packing material with different water-solid ratios from experiments,it is found that the rich-water packing material with water-solid ratio of 2.5 or even more is not suitable for filling.The water-solid ratio must be controlled within 2.0 for ensuring the stability of filling body.The relationship of stress,water-solid ratio,filling body failure is established to select the critical water-solid ratio of the rich-water packing material in the stable creep stage under load in actual engineering. |
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