Resistance to impact of porcelain stoneware tiles

Abstract

The impact resistance of ceramic tiles is an important technical requirement, especially for large size and/or low thickness slabs. The standard test for ceramic tiles (ISO 10545-5) is non-destructive: it determines the coefficient of restitution of a small sample (75×75mm2) assembled on a concrete substrate under a weak impact energy (0.27J). This method does not provide neither an impact strength nor information on the way a ceramic tile is broken by impact. In order to fill this gap, an investigation was undertaken to describe, by a phenomenological approach, how ceramic tiles break under different conditions of impact. For this purpose, unglazed porcelain stoneware tiles with different size (12×12, 25×25 and 60×60cm2) and thickness (3.5, 5 and 8mm) were assembled on a concrete basement and tested for the coefficient of restitution (ISO 10545-5) and Roesler index. Their physical and mechanical properties were determined by measuring: water absorption, porosity, bulk density (ISO 10545-3), flexural strength (EN 843-1), elastic moduli (EN 843-2), fracture toughness (SENB). The impact strength was measured by falling steel balls (50, 80, 200 and 500g) with increasing energy (from 0.2 to 6J) and with different speed at the moment of impact (from 1.9 to 5.5m/s). The effects caused by impact were visually inspected, revealing for increasing energy the formation of an impact ring, radial cracks, one or two concentric Hertzian cone fractures, a highly fractured inner zone. Such damages were quantified by measuring the impact ring diameter as well as number, length and estimated surface of radial and conical cracks. A nearly linear dependence on the impact energy was found for crack length and surface, while the ring diameter and crack number seem to follow a quadratic law. The impact strength depends on the tile thickness, but also the sample size may somehow affect the mechanical behavior under impact. A map of seven levels of damage was drawn by contrasting increasing impact energy with tile thickness: it can help to predict the tile behavior in operation and to address the correct tile type in different applications.