BS ISO 23523. Test methods for discrete polymer fibre for fibre-reinforced cementitious composites
|Standard number:||20/30383022 DC|
|Status:||Draft for Comment|
- 83.120 Reinforced plastics
- 91.100.30 Concrete and concrete products
This document specifies the test methods for discrete polymer fibre for fibre-reinforced cementitious composites (FRCC). Polymer fibre in this document means a fibre made with macromolecule substances as raw material such as aramid fibre, polyamide fibre, polyester fibre, polyethylene fibre, polypropylene fibre, polyvinylalcohol fibre. For FRCC, many kinds of and types of polymer fibres are designed and produced on various demands. However, standards of discrete polymer fibres for FRCC in the civil engineering field are not specified yet in spite of their need.
If the fibre suppliers can show the principal fibre properties such as geometry and standardized basic mechanical properties, the engineer can design, manufacture and practice more effectively. Therefore, although the standard of the fibre itself is useful for users, construction engineers and others, it is expected to be utilized primary by fibre suppliers more than those. This standard defines the test methods for discrete polymer fibre, such as diameter, length, tensile strength, initial modulus of elasticity, density, melting point, moisture content and alkaline durability as basic items. These are test methods intended for certification of a fibre and not for quality control or field acceptance. The status of the existing standards are as follows;
Test methods for composites, i.e., ISO 19044, ISO 21022, and ISO 21914 are enacted. However, they are not for polymer fibre itself. On one hand, breaking force and elongation at break for fibre itself are specified in ISO 2062, but other material properties of fibres, such as initial modulus of elasticity and thermal properties, are not specified.
Existing standards for fibres are intended for clothing textiles, ropes or strips. Test methods and unit system are different from those in the civil engineering field. Traditional unit system for textile is Tex system, in which sectional size of fibre is expressed by weight per length. The unit system is different from that used in the civil engineering field. It would be very convenience to express them by SI unit such as Newtons – millimetres.
Purpose of each testing item for several situations are described below.
For fibre design, fibre shape and mechanical properties are important for selection. Fibre length is selected for matrix composition. For example, 4 to 12 mm length fibre is suitable for a uniform matrix such as mortar, and also 20 mm or longer is required for concrete which include coarse aggregate. Otherwise, aspect ratio is important because of fibre dispersion. Tensile strength and initial modulus of elasticity are important parameters for reinforcing performance of fibres including fibre-matrix bond. Bonding strength, friction and fibre surface treatment, or other matrix related parameters are also important but these parameters are difficult to estimate generally because they are strongly related to matrix properties. Also, creep and fatigue properties etc. are not included in this standard because needs of these properties depend on the purpose of FRCC.
For fibre usage, fibre is used to charge into FRCC by weight. Reinforcing performance is related to volume fraction of reinforcement, then amount of fibre should be calculated with fibre density. And in the use of moisturized fibre products for uniform fibre dispersion, additional water amount is important for hydration. Then density and moisture content should be estimated for FRCC.
For operation stage of FRCC, thermal properties and durability against chemicals are considerable. Polymer fibre used to melt to compose small cavity and release internal pressure, then explosion will be reduced. For fire protection application, melting point of fibre is considered as priority. On the other side, fibres for FRCC should have a high durability against alkaline condition. Thus, melting point and alkaline durability are also important independent parameters of fibres.
The Fibre properties are defined as properties of the smallest unit that exists in the FRCC. In particular, the types of bundled fibres include ones that maintain the bundle even within the FRCC, and the others that disperse.