Mechanical properties of porous tiles and their correlations with microstructure and composition of the ceramic body

A survey of the mechanical properties of dry-pressed ceramic wall tiles with porous support (class BIII ISO 13006: water absorption >10%) was carried out, taking into account twenty-five samples of the Italian production. These tiles were manufactured with different bodies (majolica and earthenware) and technologies: from the traditional double firing in tunnel kilns to fast double or single firing in roller kilns. This situation determined a noticeable diversification of commercial products: traditional majolica, red and white "birapida" (fast double-fired tiles), red and white "monoporosa" (fast single-fired tiles). The objective of this work is to highlight the influence of microstructure and body composition on the following mechanical properties: modulus of rupture (MOR), Young's modulus (YM), Poisson's coefficient, fracture toughness (FT) and impact resistance. In order to better understand the mutual correlations among these variables, a statistical study (analysis of the main components and stepwise multiple regression) was performed. The results obtained allowed drawing the following conclusions: the mechanical properties of porous tiles vary in a wide range, and it is rather difficult to find significant correlations with chemical composition, microstructure or processing technology of the bodies; fast fired white bodies exhibit higher values of MOR, FT and smaller critical size of defects, due to lower porosity; red monoporosa tiles are characterized by lower values of FT, MOR and YM, due to high percentage of porosity and quartz; traditional majolica tiles exhibit low-medium values of YM and MOR, not easily explainable with porosity data, and rather higher values of FT. These features can be connected with their phase composition, richer in new formed phases, the smaller size of pores and the occurrence of microstructural defects due to a coarser particle size of dry ground powders.