The aim of this study was to determine the effect of mechano-chemical activation of fly ash on the early strength of Portland cement fly ash blends. Triethanolamine (TEA) and alkalis (NaOH or Na2SO4) were used as chemical activators. The mechanical treatment was carried out with a vibratory disc mill. The effect of activation was determined by the combination of isothermal heat conduction calorimetry over 48 h in combination with measurements of compressive strength between 1 and 28 d. Direct comparison of the features of the heat flow curves with compressive strength evolution was enabled by applying a numerical quantification method to the calorimetric results. This procedure revealed a systematic increase in early strength produced by the combination of the fly ash activation methods (grinding, TEA, alkalis). In addition, the acceleration of the pozzolanic reaction by fly ash activation was verified by replacing the cement in a cement fly ash blend by the equivalent amount of portlandite.