Meaning
State of moisture vapor pressure within the capillary pores of concrete determines the potential for shrinkage and chemical activity. The internal relative humidity represents this thermodynamic state, which declines as cement hydration consumes water and evaporation occurs. This moisture level regulates the rate of autogenous shrinkage in low water-to-binder mixtures.
Desiccation Progress
Sealed concrete experiences a drop in vapor pressure due to chemical water consumption during hydration. This self-desiccation causes the internal relative humidity to fall even in the absence of external drying. The decrease is particularly rapid in high-strength concrete containing silica fume.
Floor Covering
Successful installation of resinous coatings or vinyl tiles requires a dry concrete substrate. Measuring the internal relative humidity using in-situ probes provides a reliable assessment of slab dryness before applying finishes. ASTM F2170 specifies the drilling of test holes to a depth of forty percent of the slab thickness to obtain these readings.
If the measured humidity exceeds eighty-five percent, the adhesive is likely to degrade over time. This standardized test replaced older surface-based measurements that could not detect moisture trapped deep within the concrete.
Material Hydration
Cement hydration ceases when the moisture in the pores drops below a critical threshold. Maintaining a high internal relative humidity through wet curing ensures that strength development continues for several weeks. When the pore system remains saturated, the cement particles can hydrate fully, leading to a denser microstructure.
