Novel method suitable for decreasing the roofing tile failures generated during rapid drying

Abstract

Only few papers in which principles for decreasing the failures generated during semi and rapid drying of porous shrinking materials, for example roofing tiles, are reported. One of the main differences between the traditional and rapid drying regimes is related with the fact that during the heating step products are heated to the much higher temperatures during rapid drying. If the humidity inside the industrial drying tunnels or chambers is not controlled all the time in the prescribed range of 90 - 95 %, especially during the heating step of the rapid drying regime, crack failures will be developed. In order to inhibit the cracks generation during intensive drying the non-ionic surfactant Igepal CO-630 was added in the raw material during forming process. Various amounts of surfactant around the critical micelle concentration (CMC) were used. Five isothermal experiments were recorded, on laboratory extruded roofing tiles, for each surfactant concentration. Calculated effective diffusivity and material strength -moisture ratio (Deff-MR & MS-MR) curves were used to monitor the development of the cracks during drying and to determine the most suitable concentration of the surfactant. The explanation, how the interaction of the surfactants with clay helps the water molecules to easily move up to the surface was also reported. The application of surfactant in a recommended amount has significantly reduced the drying induced fractures in roofing tiles during its intensive drying and consequently the industrial scarp-rate was accordingly lowered.