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

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 con-ductivity, 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 computa-tional models.

Automated summary

This study introduces a new method of incorporating Phase Change Materials (PCMs) into construction materials to enhance the thermal inertia of building envelopes without compromising compressive strength. Mortars with varying water-to-cement ratios were used as base materials, and PCM was introduced into the pore structure through immersion and vacuum treatment. The study observed an increase in thermal properties and compressive strength, with the highest enhancements observed in samples with the highest PCM content. Estimation models were developed to accurately predict thermal properties and compressive strength, and a target-by-design system was created for desired combinations of properties.