種別 paper
主題 A Study of the Moisture Transport Process in Concrete as a Composite Material
副題
筆頭著者 Rajesh Prakash CHAUBE(The University of Tokyo)
連名者1 Koichi MAEKAWA(The University of Tokyo)
連名者2
連名者3
連名者4
連名者5
キーワード
16
1
先頭ページ 895
末尾ページ 900
年度 1994
要旨 1. INTRODUCTION
It is a well known fact that most of the deterioration mechanisms, both physical as well as chemical are closely coupled with the moisture transport process in concrete. In this study an attempt has been made to rationally consider the physics of moisture transport in concrete. Basic phenomenons relevant to moisture transport are formulated at the pore or micro scale which are integrated over a representative elementary volume to give macro scale mass transport behavior in a homogenous porous media. Since concrete is a composite porous material consisting of various components such as aggregates, matrix as well as interfaces and macro-defects, the concept of multiple porosity is adopted to correctly define the moisture history of concrete in space and time domains. Interaction between various components is considered at macro scale. For practical considerations the formulation is kept simple enough which can be directly used in a regular FEM code.
Ingress of moisture into the pores of concrete is a thermodynamic process, driven by the overall potential (pressure and temperature) gradients. Temperature effects are neglected in this study. Thus progress of moisture can be viewed as adsorption, condensation process. The same phenomenons also define the moisture capacity or retention characteristics of the porous media. At the macro scale concrete can be subdivided into three components. Namely, matrix made of cement paste, aggregates and interfaces between aggregate and the matrix. Role and significance of these components in the moisture transport process has already been discussed in the past by the authors. If the constitutive relations of moisture interaction between these components are known, the overall mass transport process can be predicted.
7. CONCLUSIONS
Moisture transport and retention characteristics have a direct bearing with the overall microstructure of concrete. A substantial part of porosity is unmeasured using mercury intrusion or nitrogen adsorption methods. It is observed that retention characteristic is govemed by the porosity lying in finer radii range whereas transport characteristic are primarily decided upon by larger pores. Moreover it appears that when exposed to moisture finer porosity zone exhibits a delayed response in terms of continuous decrease of liquid conductivity. From the macroscopic point of view this behavior can be attributed to an increase in the Gibbs free energy for the activation of flow.
As a composite, various transport characteristics of concrete can be obtained through computer simulation methods. Multi-porosity formulation can be a useful tool in understanding various aspects and phenomenons related to moisture transport process clearly. Effect of aggregate porosity on weight loss as well as drying shrinkage strains are successfully obtained with the present local mass transfer model. The multi-component concept of water transport is essential for unified theory of mass transport and related phenomenons of concrete.
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