Chemical and microstructural characterization of environmentally friendly alkali-activated slag cement pastes and fine-limestone aggregate concretes have been carried out after aging for 20 months and compared with 55-day-old cement pastes. Although the production of crystalline phases slowed, the cement paste continues to react. Si moves to more ordered positions, and formulae activated by Na2CO3 undergo recarbonation, producing both calcite and aragonite, of which the latter occurs mainly in the recarbonation of Ca-rich building materials known to have high durability. The reaction continues little in samples activated by NaOH/waterglass after 55 days. Elemental analysis shows the Ca/Si ratio decreasing from the center of unreacted slag grains to the outer product (Op). Elemental analyses of the cementing phase in the cement paste as well as the cementing phase in concrete specimens were quite similar. Peak shifts observed in Fourier transform infrared spectroscopy imply greater durability due to increased polymerization of Si in C–S–H, which may contain Na. Over time, more Ca dissolves from the slag and enters the Op, which was observed to be homogeneous.