Effects of microencapsulated phase change materials on chloride ion transport properties of geopolymers incorporating slag and, metakaolin, and cement-based mortars

Abstract

The addition of microencapsulated phase change materials (MPCMs) to geopolymers is a technological alternative for meeting the thermal comfort and energy efficiency requirements of buildings. However, current research is limited to the effects of MPCM addition on mechanical and thermal performances of geopolymers. New MPCM applications, therefore, require additional research on durability indicators (chloride diffusivity, porosity, absorption, etc.). The objective of this research is to examine the effects of MPCM addition on sodium chloride ion transport properties of geopolymer mortars based on a combination of blast furnace slag and metakaolin, and Portland cement based mortars. Twelve different mortars (three cement-based and nine geopolymer-based) are studied by varying the MPCM content (0%, 5% and 10%, respectively) within two types of mortar: a geopolymer mortar (GPM) and a cement mortar (CM). With this aim in view, a series of characterizations are conducted, including determination of total porosity by water saturation, analysis of pore structure distribution by mercury intrusion porosimetry (MIP), measurement of electrical resistivity, capillary water uptake, stationary-state migration coefficient “Dss” and non-stationary-state migration coefficient “Dnss”, and determination of chloride ion binding capacity. The results show that MPCM addition increases total porosity, which in turn increases capillary water absorption and decreases GPM and CM electrical resistivity. Conversely, MPCM addition also reduces critical diameter and pore connectivity, due of the agglomeration effect. MPCMs also increase chloride ion binding capacity. Both effects results in decreased stationary state migration coefficient. Finally, the study shows that the chemical reaction of GPM with chloride ions delays chloride penetration in stationary state conditions. However, the same is not true for the nonstationary state method. This demonstrates the technical limitations of this method for the characterization of GPM in comparison to CM.