Microstructure-guided numerical simulations to predict the thermal performance of a hierarchical cement-based composite material

Sumanta Das,Matthew Aguayo,Subramaniam D Rajan,Gaurav Sant,Narayanan Neithalath

doi:10.1016/j.cemconcomp.2017.12.003

Abstract

This paper presents a microstructure-guided numerical homogenization technique to predict the effective thermal conductivity of a hierarchical cement-based material containing phase change material (PCM)-impregnated lightweight aggregates (LWA). Porous inclusions such as LWAs embedded in a cementitious matrix are filled with multiple fluid phases including PCM to obtain desirable thermal properties for building and infrastructure applications. Simulations are carried out on realistic three-dimensional microstructures generated using pore structure information. An inverse analysis procedure is used to extract the intrinsic thermal properties of those microstructural components for which data is not available. The homogenized heat flux is predicted for an imposed temperature gradient from which the effective composite thermal conductivity is computed. The simulated effective composite thermal conductivities are found to correlate very well with experimental measurements for a family of LWA-PCM composites considered in the paper. Comparisons with commonly used analytical homogenization models show that the microstructure-guided simulation approach provides superior results for composites exhibiting large property contrast between phases. By linking the microstructure and thermal properties of hierarchical materials, an efficient framework is available for optimizing the material design to improve thermal efficiency of a wide variety of heterogeneous materials.

Highlights

Hierarchical materials contain structural elements which themselves have a structure [1]
A cement-lightweight aggregates (LWA) mortar, with the LWA incorporating a solid and multiple fluid phases, was used as a model composite to demonstrate the adequacy of the approach
Periodic boundary conditions were implemented on the representative volume element (RVE) to perform numerical simulations in a finite element environment

Summary

INTRODUCTION

Hierarchical materials contain structural elements which themselves have a structure [1]. Computational techniques generally overcome these drawbacks [20,21,22,23,24,25,26] This focus of this paper is on a suitable numerical modeling framework that integrates the material structure and component thermal properties to predict the thermal performance of a cementitious composite containing porous inclusions (lightweight aggregates (LWA)), which in turn are filled with different fluid phases. In the latter length scale, the system typically consists of pores that contain air, water, and/or the PCM, depending on the amount of PCMs required for a given application, and the porosity and absorption capacity of the LWA Such composites provide a wide array of benefits to buildings and infrastructure, including energy efficient building envelopes with adequate structural capacity [27,28,29,30], limiting the number and/or intensity of freeze-thaw cycles experienced by concrete in bridgedecks, thereby reducing damage [31,32], and reducing the temperature rise in fresh and hardened concrete thereby controlling thermal deformation and stress development [33].

Boundary Conditions

Numerical Homogenization for Effective Thermal Performance

Findings

CONCLUSIONS