ASTM F2420 and F2659 Surface-Based Moisture Measurement Methods
Two surface-based approaches
ASTM F2420 uses a sealed insulated hood and a relative-humidity probe to measure the RH at the concrete surface after equilibration. It is a surface measurement, not an in-situ slab measurement. ASTM F2659 is a guide for non-destructive electronic moisture meters; these meters give comparative readings, not a direct RH or MVER value.
Core rules and limits
- F2420 results depend on surface temperature, ambient conditions, and hood seal; the surface must be clean and representative.
- F2659 meters respond to electrical properties affected by moisture, salts, carbonation, and aggregate type. They are screening tools and require correlation or confirmation.
- Neither method replaces F2170 when a specification requires in-situ RH, and neither replaces F1869 when MVER is specified.
Worked example
A technician surveys a slab with an electronic meter. Readings are 60, 75, and 110 in arbitrary units. The 110 location is flagged, then tested with F2170 at 40% depth; it reads 88% RH. The meter correctly found a suspect area, but the F2170 result is the acceptance value because the specification is written in RH. The meter number alone could not prove compliance.
Traps
Do not call a meter reading percent moisture or RH. Do not test a dirty surface, over a curing compound, or in direct sun. Do not use a surface hood result as a deep-slab result. Do not ignore meter limitations with salts or carbonation.