Flowing Behavior Of Liquids Through Fracture Surfaces Of Cement-based Materials

Cracks exist extensively in cement-based materials and have important influenceon the durability and serviceability of engineering structures. The existence of crackingturns structural concrete from a continuous medium to a discrete one, which changesradically the penetration mechanism of external aggressive agents. So far, the detailedmechanisms are not clarified for the involved processes of fluid through cracks. Theinfluence of the roughness of fractured surfaces on fluid flow behavior is not clarified.This thesis studies the fluid flow behavior in single crack.Firstly, the roughness of fractured surfaces is characterized with length ratio, fractaldimension and Hurst exponent as quantified parameters. The surface topographyis scanned and the above roughness parameters are calculated through computer program.The roughness parameters consistent with material composition are chosen asthe basis for further flow behavior analysis.Secondly, the permeation device is conceived for flow study of single crack. Thedisk specimens are indented mechanically and cracked into two parts by three-pointbending. The liquid flow behavior is studied experimentally for different crack openings,different material composition and different liquids. The relationship among theflow rate, crack opening and surface roughness is discussed.At last, numerical simulation is performed for fluid flow by ANSYS and FLUENT.Parallel plate flow and flow in rough surfaces are calculated for flow rate underprescribed pressure gradient and the relevant influential factors are analyzed. In thesimulation for rough surfaces, the surface curves are extracted directly from the laserscannedsurface topology. The numerical results of flow rate are compared with theinitial rate of the experimental results and the values are comparable.From the experimental and numerical results, it is found that the flow rate acrossrough surface is proportional to pressure gradient, surface roughness as well as thecubic of crack opening. The surface roughness can be best captured by length ra- tio parameter. Moreover, under low pressure the flow behavior is non Darcien withan obvious transient process for flow rate. The involved mechanisms for unsteadyfluid(sealing effect) can be the surface dissolution, surface precipitation as well as thesurface carbonation dissolved portlandite.