When is an aggregate sample considered to be at constant mass?

An aggregate sample is considered to be at constant mass when the difference in weight between two measurements taken an hour apart is less than 0.1%. This criterion is essential in ensuring that moisture content has stabilized within the sample, which is critical for accurate testing and analysis. The 0.1% threshold indicates a high level of precision, allowing for the influence of moisture to be negligible in the sample’s mass.

This consistency is key when performing tests that rely on accurate weight measurements, such as determining the specific gravity or moisture content of the aggregate. When the weight difference falls within this range, it assures that any fluctuations due to evaporation or moisture absorption are minimal, thereby confirming that the sample is stable and representative of the conditions under which concrete is mixed and placed.

In contrast, while the other options provide varying degrees of acceptable weight differences, they do not meet the stringent standard established by the 0.1% criterion. Accepting larger differences could result in inaccurate calculations or assessments of the material's properties.