7.5 : Pore Size Distribution

In concrete, the pore size distribution significantly influences the material's properties. Capillary pores, markedly larger than gel pores, form a vast network within partially hydrated cement paste, reducing the concrete's strength and increasing its permeability. This heightened permeability leads to a greater risk of damage from environmental factors like freeze-thaw cycles and chemical attacks, with the extent of vulnerability also being tied to the water-to-cement ratio.

Adequate hydration disrupts this capillary network as new cement gel formation segments the pores, effectively enhancing strength and reducing permeability. The hydration level necessary to achieve this segmentation, and its resulting improved durability and lower porosity, is contingent on both the fineness of the cement and the water-to-cement ratio. Durable concrete can result from lower water-to-cement ratios, which require shorter curing periods to reach a specific degree of hydration.

Pore size distribution, rather than total porosity, is a more accurate measure of a cement paste's characteristics, influencing the concrete's structural integrity. Pores larger than 50 nanometers, known as macropores, substantially impact the concrete's strength and impermeability. On the other hand, smaller pores, or micropores, are significant for processes such as drying shrinkage and creep. This distribution is crucial for creating concrete that can withstand various environmental and structural stresses.