Studay On Performance Of Cement-based Composite Materials Based On Compressible Packing Model

Through the theoretical derivation from the compressible packing model and the assumption of the relevant parameters during the density calculation, the thesis applied compressible packing model to calculate density of cement-based composite materials, and investigated the combined action of the packing effect and chemical effect of mineral particles to the influences on the hardened properties and rheological properties of cement-based composite materials with low water-binder ratio.Through systematic experimental research and analysis on packing effect and chemical effect of cement-based composite materials, the main achievements are summarized as following:(1)Using the Andreasen equation, the differential distribution of particles of raw material is calculated when packing system reaches the closest packing. And then, differential distribution curve of particles of mixture with various contents is compared with differential distribution curve of particles under the closest packing. From the idea of Andreasen equation, the closer the particle differential distribution of mixed system compares with that of the closest packing system, the higher the density of system is, which is in good agreement with the calculation results of CPM model. As a result, from another aspect, Andreasen equation proves the correctness of Compressible Packing Model when it is applied to calculate the packing density of cement-based composite materials.(2)Under different water-binder ratios, the influencing factors on plastic viscosity of fresh paste are different. Under low water-binder ratio, the plastic viscosity of fresh paste depends greatly on quantity of free water, namely water film thickness. In other words, the plastic viscosity of fresh paste has direct relationship with density of mineral particles. The bigger the density is, the larger the thickness of water film is when the water consumption in certain circumstances, the lower the plastic viscosity of fresh paste is; under high water-binder ratio, with the enhancement of early cement hydration reaction and the increase of hydrated product, plastic viscosity of fresh paste depends greatly on consistence and stability degree of hydrated products. Because of the mix of mineral particle which plays as a role of"nucleus", provides more contact point for the space net structure of hydrated products and makes the hydrated product more stable, plastic viscosity of paste is improved.(3)Under low water-binder ratio, the relationship between the plastic viscosity and density of cement paste is function of attenuation and degree of attenuation is gradually weakened. In a certain variation range of density, approximate relationship between density and plastic viscosity can be expressed as follows:η= e^{(16.39107 - 47.476Φ+ 32.35506Φ2)}( R ²= 0.97068)(4)Mineral particles improve the density of hardened paste of cement-based composite materials because of physical packing and chemical packing. Under low water-binder ratio, the more the mineral particles enhance density of composite system, the higher the compressive strength is. However, because particles do not contact directly any longer, when a relatively higher water-binder ratio is applied compressive strength is not dominated by the dense packing effect. Therefore, mineral particles can sufficiently play the role of packing effect only under a low water-binder ratio.