Unusual cement performance

In recent month we found many compressive strength (CS) ASTM results were lower than internal spec. 2 weeks before this happen all parameter looks similar such Blaine, C3S, actual inert additive (IA) and raw meal residue. The IA was increased by 2% after that 2 week seems to reduce the CS lower than 2% respectally to the IA.
Immediate action was to decrease the IA by 2%. Some investigations are carried out e.g ensuring the testing method, equipments and tester consistency.
My opinion; focus to 2% and the ammount of low data. 8 data is enough to make me convince. The clinker microscopy play a role, even if the freelime is only 1%. Alternative fuel(AF) does not effect cement quality directly but clinker. Currently clinker become slighly to very porous with similar freelime. AF itself contains high moisture beside low calor value. High porousity clinker with very small size of alite and belite may resulting a severe low CS at all stages. Slugish CS is caused by belite cluster (remnant of coarse raw meal).