In fly-ash alkali-activation technology, depending on the combination of activators, deleterious reactions may result in a drop in resistance with age. This Studiy aimed to evaluate the compressive strength of alkali-activated fly ash from combined solutions of NaOH and Ca(OH)2. Three molar ratio CaO/SiO2 (C/S) were studied: 0.05 (M5), 0.15 (M15) e 0.25 (M25). Resistances order of 21 MPa (M15) and 19 MPa (M25) were reached at the age of 7 days. However, after 28 and 91 days, the resistances were 8 MPa and 7 MPa, respectively. The M5 samples showed rising behavior of resistance with age. Thus, the drop in resistance has conditioned the C/S matrices. In the 29Si NMR spectra of the M25 sample Si has decreased species Q4 (3Al) and Q4 (2Al), those responsible for the mechanical properties of activated samples.