Compressive strength results are shown in Table 6. A significant
difference between MA and AA samples was visible especially during
the first 28 days of hydration. After 3 days, the strength of AA sample
was more than four times higher than that of MA sample. As the
hydration progressed the difference between the samples decreased
and at 90 days of hydration the difference between compressive
strengths was within error. Results from TGA and FTIR indicated a
higher level of hydration and more C–S–H formation in the AA sample.
The formation of C–S–H results in strength development. Thus, a higher
strength of the AA sample was expected during both early and late
hydration stage. However, efflorescence, observed on the AA sample
after 28 and 90 days of hydration, could have a negative influence on
the compressive strength [57]. Despite the issue mentioned above, the
results indicate that both activated γ-C2S did indeed hydrate and
develop mechanical strength. In addition, mechanical strength of
mortars prepared from activated γ-C2S was double compared to the
one reported by Shi [30] on non-activated γ-C2S.