Pozzolan or slag that is to blended with cement should be tested for compliance to the activity index requirement of ASTM C595. A control mix and pozzolan/slag mix are prepared and tested in accordance with ASTM C109. After a day in the moisture room, the cubes are stored in containers and placed in an oven for 27days. The Pozzolanic/Slag Activity Index (PAI) is calculated from the average compressive strength of test mix cubes and control mix cubes.

The Strength Activity Index (SAI) of fly ash or natural pozzolans for use in Portland-cement concrete is determined using ASTM C311. This test will be used to evaluate whether the fly ash or natural pozzolan is within the acceptable level of strength development specified in ASTM C618.