Overview
ISO 22873:2021 - "Quality control for batching and mixing steel fibre‑reinforced concretes" defines principles and procedures to ensure consistent, uniformly mixed steel fibre‑reinforced concrete (SFRC) during batching and mixing so the delivered product can be sampled and tested at point of delivery. The standard targets ready‑mix production and on‑site handling where steel fibres are integrated into concrete mixes.
Key topics and requirements
- Scope and purpose
- Secures quality control of SFRC during batching and mixing to deliver ingredients uniformly mixed and suitable for sampling/testing.
- Materials
- Classification of steel fibres into five groups (cold‑drawn wire, cut sheet, melt‑extracted, shaved wire, milled blocks) and permitted shapes (straight or deformed).
- Admixtures: chemical/mineral admixtures allowed; limit chloride content (≤ 0.3 kg/m3; up to 0.6 kg/m3 only with purchaser approval). Air‑entraining admixtures recommended for freeze/thaw exposure.
- Storage: protect fibres from moisture and contamination; do not use deteriorated fibres.
- Mixture proportioning
- Add fibres without changing conventional proportions for required compressive strength in most cases; adjust paste and fine/coarse aggregate ratio when high fibre content reduces workability.
- Use of pozzolans (fly ash, slag, silica fume) as partial cement replacements to improve workability is noted.
- Avoid mixes with too much coarse aggregate (recommended to keep coarse aggregate below about 55% by absolute volume to prevent wet fibre balls).
- Batching
- Materials measured per scale; fibres batched by mass or volume with accuracy −3% / +5%.
- Scales and bins requirements; scale accuracy indications (±0.15% of total capacity or 0.4% of net applied load).
- Mixing and equipment
- Mixers (stationary or truck) must be marked for capacity and speeds and able to produce uniform mixes.
- To avoid fibre balling, add fibres to a fluid mix; recommended methods:
- Add fibres to a wet transit‑mix truck (prepare wet mix first; slump 50–75 mm higher than final desired; mix after fibre addition for ~30–40 revolutions).
- Add fibres to aggregates on conveyor belts with controlled feed (use fibre feeders/shakers).
- Mechanical/pneumatic systems and screens recommended to prevent clumps.
- Quality control tests
- Slump, air content and temperature checks at placement and when strength specimens are made; re‑testing required on failure.
Applications and users
- Who benefits: ready‑mix producers, concrete technologists, mix designers, site contractors, quality inspectors, testing laboratories, procurement/specification authors, and infrastructure owners specifying SFRC.
- Typical uses: industrial slabs, pavements, shotcrete, precast elements and other applications where steel fibres replace or supplement traditional reinforcement and uniform fibre dispersion and predictable workability are critical.
Related standards
- ISO 13270 - Steel fibres for concrete: definitions and specifications (normative reference used by ISO 22873).
Keywords: ISO 22873:2021, steel fibre‑reinforced concrete, SFRC, quality control, batching, mixing, fibre balling, slump, air content, ready‑mix concrete.