Compatibility between thermochromic pigments and Portland cement-based materials

Encapsulated reversible thermochromic (ERTC) pigments with optical properties that change reversibly with temperature have been used in building coatings to improve energy efficiency and reduce environmental impact of buildings. This work presents a detailed characterization of commercial ERTC pigments useful for this application and an analysis of their compatibility with the aggressive cementitious matrix. Chemical reactions involving the pigment are identified through the analysis of the solid phase and pore solution of a white Portland cement paste and a mortar with calcareous aggregate during the first 3 h of hydration. The results indicate that a low concentration of potassium ions in the aqueous phase is necessary with respect to the concentration of pigment microcapsules to achieve a proper stability of the thermochromic response. This condition is fulfilled in the case of mortar formulations used for building coatings, thus ensuring the viability of developing a chemically stable thermochromic mortar coating.