等温条件下混凝土质扩散系数研究

混凝土的质扩散系数（Dm）是混凝土材料的一种湿物性，它反映混凝土内部的湿份在空间上趋于均匀的能力。在混凝土温度保持不变的条件下，混凝土质扩散系数取决于材料的微观孔隙结构、初始含湿量的大小及其在空间上分布的均匀性。对同一种混凝土材料而言，混凝土质扩散系数强烈地依赖于混凝土内部的初始含湿率。本首先从湿度扩散矩的概念上论证了混凝土的质扩散系统与其平均值（Dm）的关系；接着研究平均质扩散系数代替质扩散系数以后，混凝土湿度场的变化趋势；最后讨论了两种不同质扩散系数下混凝土干缩速度、干缩应变、非均匀干缩引起的约束应力等。以北方地区拆模后的大体积混凝土为例，计算了混凝土表面最大干燥应力与干燥深度，其成果可以为混凝土表面保护设计提供参考。

Study on Mass Diffusivity of Concrete Under Isothermal Condition

Mass diffusivity is one of the moisture properties of concrete, which represents the capacity of concrete scattering internal moisture to its environment. Under isothermal condition, mass diffusivity of concrete depends on micro-pore structure, initial moisture content and its spatial distribution. For early-age concrete, mass diffusivity varies strongly with moisture. Recurring to the concept of average moisture loss, the relationship between average mass diffusivity and moisture diffusion moment is educed. With average mass diffusivity instead of mass diffusivity, the transfer tendency of concrete moisture is numerically simulated. Drying rate, shrinkage strain and restrained stress based on two kinds of mass diffusion theories are compared. At last, the maximum drying stress and maximum cracked depth of massive concrete are calculated in a case study. The results indicate that the surface stress of early-age concrete is larger than estimated by linear diffusion theory, and the drying cracks concentrate in a very localized place compared with that by temperature change. That information may be useful to surface protection design of early-age concrete.