Atomistic simulations, meso-scale analyses and experimental validation of thermal properties in ordinary Portland cement and geopolymer pastes

Abstract

Ordinary Portland Cement (OPC)- and alternative binder-based materials have been widely used in Thermal Energy Storage (TES) applications due to their excellent TES capacities, good mechanical properties and low-cost. In this attempt, this work proposes an upscaling procedure to model the TES properties of two hydrated pastes made of OPC and a Hybrid cement (i.e., an alternative H-Cement binder), the latter employed for a GEOpolymer-based composite (GEO). Firstly, an atomistic approach based on energy minimization and molecular dynamics is employed for modelling the thermal behaviors and heat storage capacities of CSH (calcium silicate hydrate) and NASH (sodium aluminosilicate hydrate) phases, being those the main phases for OPC-based paste and GEO, respectively. Then, an up-scaling optimization procedure and meso-scale FEM homogenization techniques are proposed to link the TES parameters of the atomistic main phases of OPC-based paste and GEO with the homogenized upper meso/macro scale values. To this end, the results of an experimental program on both OPC and GEO pastes have been considered as benchmark to calibrate/validate the numerical tools. Promising simulations at several scales and up-scaling procedures are demonstrated in terms of homogenized temperature-dependent heat capacity and thermal diffusivity, showing a good agreement with the experimental data of the analyzed mixtures.