To determine the impact resistance of the tiles.
INTRODUCTION
The strength of ceramic tiles is important for their service life. Stresses are imposed upon tiles because of size changes within backgrounds and even from poor-quality adhesives. Floor tiles are expected to sustain many types of loads, some of which may be static but impact loads also occur. Impact loads provide the most usual way for breakages on walls.
Apparatus Required:
A diagram of a basic form of apparatus is shown in Figure 3. The vertical steel bar supports an electromagnet used to release steel balls at particular heights and may hold a scale for determining heights of rebound. In the version proposed for standardization, the height of drop (h.) is fixed at 1 m and the rebound height (h2) is determined by timing the difference between the first and second bounces and converting this electronically to the coefficient of restitution. Individual tiles may be measured by support on three studs in the form of an equilateral triangle but the preferred method uses tiles adhered with a rigid epoxide resin adhesive to concrete blocks. The steel ball impactor is 19 mm in diameter, with a mass of 28 g.
Materials Required:
- Floor Tiles
- Wall Tiles
THEORY AND PROCEDURE:
MEASUREMENT OF IMPACT RESISTANCE
Coefficient of restitution
The most suitable property to measure is the coefficient of restitution, e, between the floor or tile and a steel ball. The coefficient of restitution between two impacting bodies is defined as the relative velocity of departure divided by the relative velocity of the approach. For a ball impacting a flat static surface
e =
u
Now v = √ 2gh,
and u = √2gh,
h2
ev
h1height of drop
h, the height of the rebound
In a purely elastic impact with no energy losses due to heat, sound, or friction, e would equal one. However, all impacts are less than perfect and a value of e less than 1 is always obtained. The lower the value the more energy has been permanently lost at impact. If the impact is not 100% elastic, then energy will be used to rupture the surface or cause a permanent plastic deformation. In the case of a steel ball impacting ceramic tiles, it can be assumed that heat, sound, and friction losses are constant and so the value of e will give a measure of the permanent damage sustained at impact. Thus, a quantitative assessment of the ability of the tiling to withstand impact can be made.
Applications
The technique is primarily used in the laboratory to assess the strength, such as the coefficient of restitution, of tiles. For this, the concrete blocks and epoxide resin adhesive are constant while the only variation is in the tiles. Some comparative results are shown in Table 3.
Table 3. Examples of Coefficients of Restitution (c) for Tiles in Standard Test Units
Description
152 x 152 x 7 mm Buff vit
e
0.87
152×152 x 10 mm
0.87
Buff it.
0.91
152 x 152 x 8 mm
Grey fully vit.
152×152 x 11.5 mm 0.93
Grey fully vit.
152×152 x 16.5 mm
0.94
Grey fully vit.
152 x 152 x 7mm
0.90
Red vit.
152 x 152 x 11 mm
0.91
Black vit.
108 x 108 x 3.5 mm
0.59
152
x 152 x 5.5 mm
0.66
152 x 152 x 7 mm
0.69
152×152 x 10 mm
0.63
Glazed wall tiles
202 x 202 x 8.5 mm
0.73
Glazed floor tiles
152 x 152 x 8.5 mm
0.91
Engobes vit.
Vitrified dust-pressed floor-tiles
The effect of increased thickness can be seen for otherwise similar tiles. In the case of the glazed wall tiles, the 10 mm-thick tiles do not have the same body formulation as the other thicknesses. If a comparison between the effects of different adhesives is required then the tiles and concrete base are standardized. The technique has also been used in the laboratory to establish the degree of support given by different types of bases or backgrounds. For example, plasterboard, polystyrene, and mortar supports have been compared using this technique.
Point and Edge Impacts of Glazed Floor Tiles
General
Glazed floor tiles, especially those with the more porous bodies are prone to damage from pointed objects whereas unglazed vitrified floor tiles are rarely damaged in this way.
Point Impacts
To stimulate point damage on the face of tiles the coefficient of restitution apparatus (Figure 3) is used but the ball impactor, C in Figure 4, is replaced by a bullet-shaped piece of hardened steel (a) 56 mm long, 6mm maximum diameter and 12.5 g mass. The impacting head has a radius of curvature of approximately 1
mm.
Diagram of dropping-ball apparatus for measuring the cost of return
Tiles are assessed for resistance to point impact damage by comparing the damage sustained against four types of tiles, which were selected from a range of tiles
subjected to the standard point impacts. This enables the classification of Ito 4 to be assigned, class 1 having craters of approximately 3 mm diameter and the glaze completely removed, and class 4 having craters confined to the glaze only, with a maximum diameter of 1.5 mm.
Edge Impacts
Resistance to edge impacts is assessed using the steel impactor (b) in Figure 4. The maximum diameter is 19 mm and the barrel length is 60 mm. The mass is 127.3
The impacting point has a radius of curvature of 1 mm. The method utilizes a pendulum apparatus (6) and impacts are made with the point of the impactor striking the tile surface at right angles. The first impact is made at a Site approximately 1 mm from the edge of the tile and, choosing fresh sites for each impact, the distances from the edge are increased by 1mm ate time until impacts fail to chip the tile. The distance from the edge is therefore a measure of the edge impact resistance, the lower the value the better the impact resistance. In practice, the type of grouting material, the width of the joint, and the efficiency of the filling provide some resistance to edge damage. Considerable variations can therefore occur in service but the measurement technique enables tiles to be compared and their vulnerability to damage assessed where joints are poorly filled.