Overview
ISO 18650-2:2025 - "Building construction machinery and equipment - Concrete mixers - Part 2: Procedure for examination of mixing efficiency" defines a standardized test procedure to evaluate the mixing efficiency of batch-type and continuous-type concrete mixers (as defined in ISO 18650-1). It is applicable to mixers with a rated capacity ≥ 0.5 m3 and is the third edition updating the 2014 version. The standard specifies concrete mix preparation, sampling locations and volumes, test methods, evaluation criteria and reporting requirements for a reproducible assessment of mixer performance.
Key topics and technical requirements
- Scope and applicability: batch and continuous mixers ≥ 0.5 m3.
- Mix design and conditions: typical test mix uses coarse aggregate up to 20 mm or 25 mm, slump (80 ± 30) mm, air content (4.5 ± 1.5) %, nominal compressive strength (25 ± 5) N/mm². Constituent materials weighed within ±3% uncertainty.
- Mixing times:
- Batch-type gravity mixers: 60 s for ≤ 1.0 m3; add 5 s per 0.5 m3 increase above 1.0 m3.
- Batch-type compulsory mixers: 30 s for ≤ 3.0 m3; add 15 s per 1.5 m3 increase above 3.0 m3.
- Continuous mixers: mixing time equal to residency in chamber, minimum 10 s.
- Sampling protocol:
- Two portions sampled immediately after prescribed mixing time.
- Minimum sample volume: 20 L for batch mixers, 100 L for continuous mixers.
- Sampling positions defined for different mixer designs (e.g., concentric zones for pan/turbo mixers, front/rear/centre for paddle mixers, beginning/end of discharge for gravity mixers).
- Variance tests and measured parameters:
- Air content, mortar content (per unit volume), coarse aggregate content (per unit volume), and consistency (slump).
- Compressive strength testing of specimens (cubes or cylinders).
- Efficiency quantified by variance ΔX = (X1 − X2) / ((X1 + X2)/2) × 100, where X1 and X2 are paired portion results.
- Performance evaluation and reporting: criteria for acceptable variances, test-report structure and required manufacturer/mixer verification checks (e.g., RPM conformity, restart capability, discharge design, loss