Preliminary Study On Characteristics Of Structure Of Voids In Particle Assemblies Generated By PFC3D

The permeability of cement paste and interfacial transition zone are main factors that influence the permeability of concrete. The characteristics of the structure of voids of the particle assemblies in both interior area and interface area created by PFC3D software, is supposed to reflect some properties of the pore structure of cement paste and interfcial transition zone of concrete. The characteristics of structure of voids include porosity, pore size distribution, ratio of connected voids and genus. The ratio of connected voids and genus are parameters that discrible the connectivity of the structure of voids. They are influenced by the scale of the pixels which generate the structure of voids.The influence of the gradation and dimension ratio of the particles on the interior structrure of voids is studied. The result indicates that the porosity of the particle assemblies compacted by gravity is about 20% to 45%. The particle assembly of which grading curve follows the Fuller curve has a relatively lower porosity and higher genus. It means that the assembly is denser and has more complex structure of voids. Compared with other assemblies, assembly of spherical particles is more compact, and its structure of voids is more complex. Particle size distribution affects the porosity of the particle assemblies. The assemblies with wider particle size distribution have lower porosity. The connectivity of the structure of voids is more sensitive to the content of small particles whose radiuses are close to the pixels. With more small particles, the assembly has a lower connectivity and a higher genus, which suggests its structure of voids is more complex. The ratios of connected voids of all the assemblies are almost 100%.The influence of gradation and dimension ratio of the particles on structrure of voids at the interface is also investigated. The result indicates that the interfaceial area has a higher porosity and genus compared with the interior area. It implies the permeability of the interface area is higher than that of in the interior area. The gradation and shape of the particles has an influence on the structure of voids of the interfacial area, which is similar with the interior area. The ratio of connected voids of all the assembly is almost 100%, too.The parameters of the structure of voids of particle assemblies such as connectivity and genus, which can not be examined by experimentation, can be touched by numerical simulation. This method can be used to study the permeability of concrete in the future.