Rationale

The proposed revision is to extend the measurement period to 28 days by adding required readings at 21 and 28 days after immersion. Many specifications already reference 28 day expansion limits for assessing potential ASR. Extending the duration to 28 days aligns the test procedure. The additional data points provide a more complete characterization of the aggregate reactivity, especially for slowly reactive materials where 14 day results may not fully capture long-term behavior.