This work presents a study about alkali-activation of Portland cement pastes and mortars by Na2O, K2O, Na2SiO3 and K2CO3, in proportions of 0, 3, 5, 10 and 15%, in weight. The aim was correlate the microstructures formed with the properties developed in the fresh and hardened stages. The results show that the alkalis changes the chemical equilibrium of all hydrates formed, and this promotes lower compressive strength in final ages. Quickly setting times and early-high compressive strengths have been obtained with alkalis, but as Na2SiO3 and K2CO3 were more efficient.
