【作者】 马明军；

【导师】 李克非；

【作者基本信息】 清华大学 ， 土木工程， 2009， 硕士

【摘要】 水泥基材料在工程应用中广泛存在着各种裂缝，裂缝对结构的耐久性和适用性都会产生明显的影响。裂缝的存在使结构混凝土材料从连续介质变为非连续介质，导致外部侵蚀性物质向混凝土内部的迁移过程发生根本改变。目前对流体通过裂缝表面传输的物理化学规律并不清楚，无法确定裂缝断裂表面特征对渗流规律的影响。本论文对水泥基材料单一裂缝开裂表面的流体流动规律进行研究，分别从以下三个方面进行：首先，研究界定断裂表面粗糙性能的参数，主要集中在长度比、分形维和均方差粗糙度等参数。用大尺度激光扫描仪对开裂试件表面进行激光扫描，得到断裂表面粗糙状况的真实三维数据，编制计算程序计算了断裂表面的粗糙度，通过对各粗糙度与实际材料特性的比较分析，选取与材料组成特征相一致的参数作为粗糙面表面形貌界定的基准。其次，设计实验方案，用岩石切割机在试件上切出单一刻槽，在Toni试验机上做三点抗弯试验制造单一裂缝，设计渗流试验装置并进行不同配比、不同裂缝宽度和不同渗流液体的试验。在此基础上分析了在单一裂缝存在下，流过粗糙表面的流量与流体性质、压力、裂缝宽度以及表面粗糙度等因素的关系。最后，分别用ANSYS和Fluent数值工具模拟计算了Poiseuille平板流模型，作为数值分析与实验结果比较的基准值。进一步，按照扫描得到的粗糙面进行实际模拟计算，分析了数值分析的流量结果及其影响因素。综合试验结果，对单一裂缝下水泥基材料的流动规律进行研究，并讨论了渗流过程呈非稳态的原因。研究结果表明，流体经过单裂缝水泥基材料断裂表面的流量与渗透压力梯度、裂缝表面粗糙度指数和裂缝宽度的三次方成正比，与流体粘度成反比，表面分形维和线性长度比可以有效地表征与渗流流量相关的裂缝粗糙度。实验发现，单裂缝间渗流并不是一个稳态的过程，而是具有明显的非稳态特征。导致非稳态的原因是渗流物理规律以及流体与裂缝表面物质发生物理沉淀，冲蚀和水泥二次水化和碳化过程。更多还原

【Abstract】 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.更多还原