LAUSR

Abstract Enhancement of thermal performance of concrete wall is nowadays of great importance in reducing the operational energy demand of buildings. We developed a new kind of inorganic coating material based on SiO 2 - Al 2 O 3 -rich minerals and Portland cement (PC) powder. The finely pulverized mineral powder with the particle size distribution (PSD) of 0.4–40 μm was mixed with the vehicle solvent containing some agents, cement powder with PSD of 2–100 μm, and water in the certain weight ratio, producing the colloid solution. After application within 2 h to the plaster layer of concrete wall and sufficient long hardening period of over three months, the coating layer of 0.6–1.0 mm thickness was observed to become a densified ceramic. Powder X-ray diffraction (XRD) experiments were performed to identify the crystalline components of minerals, cement and ceramic coating powders. Three- and two-dimensional surface morphologies and chemical compositions of coating material were obtained with the optical interferometer and scanning electron microscope (SEM) equipped with an energy dispersive X-ray analyzer (EDX). These XRD and SEM/EDX analyses demonstrated obviously that the coating layer is mainly composed of the calcium-silicate-hydrate (C-S-H) and the calcium-aluminate-hydrate (C-A-H) ceramics with the relatively small number of closed pores (10% porosity) compared with the cement mortar and concrete layers. Two-step hydrations of cement and subsequently SiO 2 - Al 2 O 3 promoted by the alkali product Ca ( OH ) 2 were proposed as the main mechanism of ceramic formation.