ISO 23523:2021 pdf free download – Test methods for discrete polymer fibre for fibre-reinforced cementitious composites.
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 fibre-reinforced cementitious composites (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 despite the need for it.
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 used primarily by more fibre suppliers than those.
The status of the existing standards is as follows;
1) Test methods for composites exist, i.e. ISO 19044, Iso 21022 and ISO 21914. However, they are not for polymer fibre itself. Breaking force and elongation at break for the 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.
2) 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. The traditional unit system for textile is the 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 convenient to express them in SI units such as Newtons — millimetres.
The purpose of each testing item is described below.
For a fibre design, the fibre shape and mechanical properties are important for selection. The fibre length is selected upon the matrix composition. For example, a 4 mm to 12 mm length fibre is suitable for a uniform matrix such as cement mortar, and 20 mm or longer is required for concrete that includes coarse aggregates. The fibre diameter is also important because it influences the fibre dispersion through the fibre aspect ratio (length/diameter). The tensile strength and initial modulus of elasticity are key parameters that influence the reinforcing performance of the fibre through the fibre-to-matrix bond. On the other hand, the bonding strength, friction and surface treatment of fibre, in spite of their importance, are not included in this document as they are strongly related to the matrix properties and are generally difficult to estimate. In addition, creep and fatigue properties are not included in this document either because the needs of these properties depend on the application situations of the FRCC.
In terms of fibre usage, the fibre reinforcement performance in the FRCC is related to the fibre volume fraction, which is calculated from the fibre weight according to the fibre density. In the use of moisturized fibre products for a uniform fibre dispersion, the existence of water can have a significant effect on the hydration of the cementitious matrix. Thus, the fibre moisture content needs to be accurately estimated.
For the operation stage of the FRCC, their thermal properties and durability against chemicals are of particular concern. For instance, in case of high strength cementitious composites, the polymer fibre can melt during a fire to introduce small cavity so as to release the high internal pressure and consequently reduce the risk of an explosive failure of the cement matrix. Therefore, for fire protection applications, a relatively low melting point of the fibre is considered as apriority.