High thermal inertia mortars: New method to incorporate phase change materials (PCMs) while enhancing strength and thermal design models

Abstract

This study proposes and tests a new method to incorporate Phase Change Materials (PCMs) into construction materials to increase building envelopes' thermal inertia without causing a decrease in the material's compressive strength. Mortars with three water-to-cement ratios (0.45, 0.55, 0.65) and, therefore, different porosity were used in this study as base materials. Following our novel procedure, PCM was incorporated into the pore structure of hardened samples through immersion into heated PCM in a liquid state and vacuum application for three different vacuum periods (15 min, 1 h, and 4 h). Final porosity, absorbed PCM volume, thermal conductivity, thermal effusivity, and compressive strength were determined. An increase in all studied properties was observed. The maximum enhancement was observed in samples with 0.65 w/c and 4 h of vacuum, which corresponded with the samples with the highest PCM incorporated (7.01 % of PCM by sample volume). This maximum increase was 17.86 % in thermal conductivity, 24.68 % in thermal effusivity, and 22.59 % in compressive strength. Besides, estimation models for the thermal properties and compressive strength were developed, showing high accuracy (errors lower than 10 %). These estimation models were combined to create a target-by-design system that determines the initial porosity and PCM content required to obtain a desired combination of compressive strength and thermal conductivity or effusivity. The thermal conductivity and effusivity of the solid part of the mortar (excluding the air) were obtained based on these models. These values can be very useful as an input for simulating the thermal behavior of cementitious composites using computational models.