| The rheological properties of fresh cement asphalt emulsion(CA) paste can determine whether CA mortar has good flowability and uniformity or not, which is the key to the success of CA mortar construction. Some problems, such as segregation, bleeding, rapid demulsification rate of asphalt emulsion, would be easily appeared in the placement of CA mortar and affect its performance in service. The main reason for these problems is that fresh CA paste cannot posses s good rheological properties. As a result, fresh CA paste cannot prevent sand from sediment and keep a good workability for certain time. How to control the rheological properties of fresh CA paste and reveal its development law as well as the corresponding mechanism is the key to sovle the problems. Therefore, the rheological properties of fresh CA paste are studied in this paper, such as viscosity prediction of fresh CA paste, the relationship between viscosity and yield stess, factors influencing viscosity and yield stress, thixotropy, the relationship between the viscosity development law and the interaction of asphalt emulsion and cement.In the basis of some theories of suspension rheology, factors influencing the yield stress and viscosity of suspension are analyzed, and the viscosity and yield stress prediction models are proposed to study the viscosity and yield stress of CA paste. Effect of the rheological properties of CA paste on the uniformity and flow-ability of CA mortar is discussed. The design principle of CA paste is proposed based on viscosity and yield stress. Discussions indicate that CA paste should possess a certain yield stress and a lower viscosity to guarantee that CA mortar can have a high flow-ability and also a good resistance to sand settlement.In the basis of the viscosity prediction of suspension, viscosity of CA pastes with different mass ratio of asphalt emulsion to cement is predicted through experimental data. Based on the original prediction results, a viscosity predicti on model for CA paste with any given(AE/C) is proposed. In the model, the viscosity of CA paste can be predicted by particle volume fraction, maximum particle packing density and coefficient b. The maximum particle packing density of CA pastes can be determined by the volume fraction of asphalt in asphalt-cement system. The b value is 0.6 for CA pastes with anionic emulsion and 0.4 for CA pastes with cationic emulsion. The proposed model do offer a simple and reliable method for viscosity prediction of CA pastes with any given AE/C.In the basis of the viscosity and yield stress prediction results, the relationship between viscosity and yield stress of CA pastes with different AE/C is established. Combined with the design principle on the rheological properties of CA paste, the weakness of the relationship between viscosity and yield stress of CA paste is analyzed. In order to improve this relationship, factors influencing the viscosity and yield stress of CA paste is studied. Results indicate that CA paste has very low yield stress compared to cement paste at the same viscosity, therefore, sand can easily settle in CA paste at static state. The stability of asphalt emulsion affects the growth rate of plastic viscosity of CA paste, and superplasticizer dosage affects the growth rate of yield stress, which both affect the retention ability of good fluidity. Viscosity modifying agent can greatly improve the yield stress of CA paste, which is the key to guarantee the uniformity and flow-ability of CA mortar.For hysteresis loop test, shear rate decay test and structure parameter test are all not suitable to evaluate the thixotropy of CA paste, a new method is proposed to evaluate the thixotropy of CA pastes, in which, initial strucuture parameter and structure parameter rebuilding rate is employed to study the flocculation rebuilding process of CA paste, and de-flocculation characteristic time is to evaluate the de-flocculation rate of CA paste. Results indicate that the flocculation rebuilding rate of CA paste decreases with the increasing AE/C. However, the de-flocculation characteristic time of CA paste is longer than cement paste, and increase a lot in the first 5 minutes. The equilibrium shear stress of cement paste can keep unchanged for certain time, but its value of CA paste increases with resting time.Effect of asphalt emulsion on cement hydration is analyzed through setting time, cement hydration and X-ray Diffraction test. Demulsification process of asphalt emulsion in CA paste is studied by laser particle analyzer and optical microscope. Combined with the viscosity development of CA paste, the relationship among viscosity development of CA paste, cement hydration process, and demulsification process of asphalt emulsion is revealed. Results indicate that the retarding effect of asphalt emulsion on cement hydration is mainly due to the retarding effect of emulsifier on cement hydration. Cement hydration has induction effect on demulsification of asphalt emulsion, but it cannot completely dominate the demulsifying rate of asphalt emulsion. In the demulsification process of asphalt emulsion, the size growth and morphology change of asphalt droplets can increase the viscosity of CA pastes. Therefore, the viscosity development of CA paste can be as an index to reflect the demulsification process of asphalt emulsion in CA paste.Through the above study, a viscosity prediction model is proposed for CA paste, and the rheological behavior, thixotropical behavior, and the viscosity development and its correpsonding mechanism, is revealed in the paper. The work can provide some theories and to understand the construction mechanics behavior of CA paste and design CA mortar in placement. |
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