Standard EN envisages two magnitudes for the evaluation of mechanical strength:

Size: px

Start display at page:

Download "Standard EN envisages two magnitudes for the evaluation of mechanical strength:"

Eleanore Booker
6 years ago
Views:

1 BENDING STRENGTH Given the slimness of ceramic tiles, which have large length and width dimensions in respect to thickness, bending strength is indicative of the mechanical strength of the tile as a whole in relation to aggressions of differing nature, such as live and dead loads, rolling actions, and impacts. Standard EN envisages two magnitudes for the evaluation of mechanical strength:, in direct relation to the load applied on to the tile, with a corrective coefficient that relates the distance between supports and the width of the test piece, expressed in Newtons (N). The result of the test is a function of tile thickness for the same type of material. The modulus of rupture, also termed bending strength, which is derived from the magnitude breaking strength by a mathematical formula [breaking strength divided by the square of the minimum thickness at the rupture cross-section]. The result of the test, expressed in Newtons per square millimetre (N/mm 2 ), provides the approximate mechanical strength of the ceramic tile independently of tile thickness. is an essential characteristic that the manufacturer shall state in every case, also on the CЄ mark for tiles that are not first-quality tiles. according to ISO International standard ISO establishes a test method for the determination of bending strength or modulus of rupture, and breaking strength for all types of ceramic tiles. The modulus of rupture is only measured in tiles whose breaking strength is below 3000 N (Newtons). The test method envisages the following magnitudes: Physico-chemical characteristics 1

2 CODE CHARACTERISTIC DEFINITION F C S R Breaking load Breaking load on entire piece or Modulus of rupture Force necessary to cause the test piece to break, expressed in Newtons (N), according to a pressure gauge reading. In this case the test is conducted on the entire tile, this being the most representative test. Force expressed in Newtons (N), obtained by multiplying the breaking load (F) by the ratio of the distance between the supporting rollers ( in mm) and the width of the test piece (b in mm). Breaking strength S= F (in Newtons) Magnitude expressed in Newtons per square millimetre (N/mm 2 ), obtained by dividing the breaking strength by the square of the minimum thickness at the rupture cross-section. Bending 3F 3S strength R = = (in N/mm 2 ) 2 2 2bh 2h Note: The modulus of rupture is an intrinsic tile characteristic; i.e. two ceramic tiles made by the same process and differing solely in thickness will have the same modulus of rupture, even though the force required to break them is much larger in the thicker tile. b Of the foregoing definitions, the tile fixer needs to remember breaking strength (S), expressed in Newtons (N), and bending strength or modulus of rupture (R), expressed in Newtons per square millimetre (N/mm 2 ). Both magnitudes shall be stated in the technical documentation supplied by the manufacturer and, in addition, are part of the CЄ mark and label, according to Annexes ZA and ZB of standard EN 14411: Physico-chemical characteristics 2

When tiles are intended for roofing, breaking strength or bending strength shall be stated. When tiles are intended for flooring, breaking strength shall be stated.

3 When tiles are intended for roofing, breaking strength or bending strength shall be stated. When tiles are intended for flooring, breaking strength shall be stated. The formulas given above have an experimental character, in which: : distance or span between the supporting rollers b: test piece width h: minimum thickness, expressed in millimetres, of the test piece at the rupture cross-section, measured after the test The bending strength calculation is based on a rectangular cross-section. In the case of tiles with non-uniform thickness, the minimum thickness measurement at the rupture cross-section only provides approximate results. The less pronounced is the relief, the closer is the approximation. Apparatus for the breaking load test Physico-chemical characteristics 3

4 Minimum values required by standard EN REQUIRABE MINIMUM VAUES FOR BREAKING STRENGTH AND MODUUS OF RUPTURE IN EXTRUDED TIES ISO tiles of thickness 7,5 mm Modulus of rupture (**) PRODUCT GROUP AI a AI b AII a-1 AII a-2 AII b-1 AII b-2 AIII /21(*) / / / ,5/ /8 8/7 REQUIRABE MINIMUM VAUES FOR BREAKING STRENGTH AND MODUUS OF RUPTURE IN PRESSED TIES ISO tiles of thickness 7.5 mm Modulus of rupture (**) tiles of thickness 7.5 mm PRODUCT GROUP BI a BI b BII a BII b BIII /32 35/ /27 30/ /20 22/ /16 18/ (*) Average value/smallest value of the sampling (**) Not applicable to tiles with breaking strength 3000 N Modulus of Rupture = Bending Strength In the documentation of the Tile Installation Project [Instituto de Promoción Cerámica, CD-ROM Guía Electrónica de la Tecnología de Colocación de Baldosas Cerámicas, 1997], it was advised, as an orientation, to assign minimum bending strength values based on intended tile use: C (or S) (*) 450 N in tiles intended for wall cladding C (or S) 900 N in tiles intended for flooring with exclusively pedestrian traffic C (or S) > 2000 N in tiles intended for flooring with not exclusively pedestrian traffic (*) C is the breaking load (indicated by the dynamometer at the moment of rupture), when the test is performed on the entire tile S is the breaking strength, as defined in standard test method ISO , on a test piece cut from an entire tile, derived from the expression: S = F x (in Newtons) where : B F B is the breaking load of the cut test piece (in N) is the distance between the supporting rollers (in mm) is test piece width (in mm) Physico-chemical characteristics 4

5 In flooring subject to not exclusively pedestrian traffic, with important live and dead loads (for example, mechanical or hand pallet cars with narrow wheels), it is the specifications writer who should determine the minimum requirable breaking strength or load, and the tile installation materials and technique, as well as the hand-over conditions and performance requirements of the substrate, and recommend: Selection of tiles smaller than 30x30 cm Minimum thickness of at least 11 mm Modulus of rupture of at least 27 N/mm 2 (AI a, AI b, BIa or BI b tiles) Selection of unglazed tiles (UG) If possible, meeting code P 4s requirements according to the French NF- UPEC classification Physico-chemical characteristics 5

CHARACTERISTICS IN STANDARD EN 14411

CHARACTERISTICS IN STANDARD EN 14411 S IN STANDARD EN 14411 European standard EN 14411 establishes a set of physico-chemical characteristics that need to be taken into account in ceramic tile as a function of the tile s intended use as flooring