Influence of Different Types of Fly Ash on Properties of Ternesite–Ye’elimite Cement

This study explores the effect of three types of fly ash (FA) on the hydration and performance of ternesite–ye’elimite (TY) cement. The inclusion of fly ash delayed the setting time due to the dilution effect, with FA1 causing the most significant delay. Incorporating 30% fly ash resulted in a decrease in compressive strength, with FA2 causing the greatest reduction. All three types of fly ash in TY cement exceeded the reactivity threshold set by the standard. FA1 and FA3 exhibited better reactivity than FA2, which was associated with higher content of amorphous SiO2 and Al2O3. After 28 days, the hydration of ternesite facilitated the formation of ettringite (AFt), and strätlingite was detected in pastes containing FA1 and FA3, indicating higher reactivity than FA2. The appearance of strätlingite in pastes with all three types of fly ash after 90 days confirmed that fly ash significantly contributed to hydration through its pozzolanic effect.