Thermal and water transfer in cementitious porous medium: thermal building and durability

Xiaoyan Ma ,Farid Benboudjema,Rachid Bennacer

doi:10.1051/matecconf/201824001023

Abstract

Cementitious materials are typical porous medium, which are widely used in civil engineering and thermal buildings. The thermal and hydrate properties of the material are fundamental to predict accurately the energy needs and the reliable duration of the structures in a long term. Due to the complicated coupling, the thermal capacity, conductivity and source term in energy equation are affected by the humidity distribution and the microstructure evolution of the porous materials. The coupling relation of thermal and hydrate properties are summarized in this work, the coupled drying model is discussed, and the experiment is performed to verify the simulation results for RH (Relative humidity) and ML (Mass loss). Two approaches are adopted to estimate the humidity/water content profile in the porous medium and to analyse the temperature effect. In addition, the equivalent hydrate capacity and conductivity are identified as function of humidity. The significance of this work lies in predicting the energy demand, the long-term thermal behaviour, taking into account the change of the thermal cementitious materials properties during their service time. Such inner structure is consequence of the system durability where the temperature, water content and humidity will act on the cracks settling within the material.

Highlights

The performance of thermal building is dependent on the properties of wall materials and their evolution overtime
The equivalent diffusion coefficient and equivalent hydrate capacity is calculated as function of humidity. This information is fundamental for optimizing the hydrate and thermal properties and in the long-term predicting the durability of the cementitious materials
The relative humidity provide a local information of the moisture distribution, while the mass loss is the integral of water content over the domain, meaning the global water loss during the drying process

Summary

Introduction

The performance of thermal building is dependent on the properties of wall materials and their evolution overtime. The difficulties lie in the complexity of cementitious porous media, the strong coupling between temperature effect and humidity/water sorption, and the inaccurate energy source term induced by the phase change (evaporation/condensation process). The values of thermal conductivity coefficient increase with the increase of liquid content in pore [8] Another coupling of heat and mass during drying or wetting process is the local energy source term, representing the evaporation or condensation. The equivalent diffusion coefficient and equivalent hydrate capacity is calculated as function of humidity This information is fundamental for optimizing the hydrate and thermal properties and in the long-term predicting the durability of the cementitious materials

Experiment and analytical solutions

Drying model

HR ρl2RT μl Mv

Results and discussion

Conclusion