The influences of lithium, potassium, and sodium additions on the hydration rates and developing pore structure of portland cement pastes have been presented. While the different alkali additions exhibited some common effects, such as their acceleration of early age hydration, their influence on long term hydration and porosity percolation were observed to be different. Lithium additions were observed to avoid both a decrease in long term hydration and a repercolation of the capillary pores at later ages. The differences in porosity percolation were explained based on the likely influences of alkali additions on C-S-H gel morphology and molar volume. In the low alkali cement paste prepared in this study, repercolation of the first depercolated capillary pore and open gel pore networks occurred due to long term aging effects, even under saturated curing conditions.