再生骨料影响混凝土渗透性的数值模拟

出于环境保护及经济方面的考虑，再生骨料在混凝土生产中得到越来越多的应用。混凝土可认为是由天然或再生骨料、多孔基体和界面过渡区三相组成的复合材料。基于随机骨料结构生成算法，建立了三相混凝土数值模型并应用于气体渗透性的分析。对于混凝土二维数值模型的稳态渗透问题，应用有限单元法求解压力场，并基于压力-流量的宏观等效关系计算混凝土材料的总体渗透率。数值分析结果表明:1) 总体渗透率随过渡区厚度及其相对渗透率的增加而非线性地增长；2) 由于骨料的存在而导致的稀释效应及曲折度效应是影响混凝土总体渗透性的两个重要因素；3) 再生骨料渗透率对混凝土宏观渗透率的影响呈“S”形曲线的关系。出于控制回收骨料混凝土渗透性能的考虑，回收骨料的渗透率最好比砂浆基体的渗透率低一个数量级，同时回收骨料的掺量也需要合理选择确定。

NUMERICAL ANALYSIS OF GAS PERMEABILITY OF CONCRETE INCORPORATING RECYCLED AGGREGATE

The utilization of recycled concrete aggregates(RCA) in a new concrete production has been increasing due to environmental and economic considerations.In this paper,concrete is considered as a random heterogeneous porous composite including three phases: natural or a recycled coarse aggregate,a porous matrix and an interfacial transition zone(ITZ) between them.Numerical samples for gas permeability analysis are established through a random aggregate structure(RAS) scheme,each numerical sample containing randomly distributed aggregates coated with ITZ and dispersed in a homogeneous matrix.Then the finite element method(FEM) is used to solve the steady permeation problem on a 2D numerical sample and the overall permeability is deduced from a flux-pressure relation.From numerical results,the following observations are obtained: 1) overall permeability increases non-linearly with the width and relative permeability of ITZ;2) the dilution and tortuosity effects of aggregates on gas flow through the porous matrix are two predominant factors for permeability estimation;3) the directional contribution of coarse aggregates on overall permeability shows an "S" shape curve behaviour.For high durability performance RCA with,it is preferred that the permeability should be at least 1 order lower than matrix.The replacing ratio of RCA should also be determined reasonably.