ABSTRACT
Cementitious materials are porous. The size of the pores in hydrated cement materials varies from the micron to the nanoscale. Three main categories of pores are often quoted. The first category is the compaction/air voids. They are the largest pores in a cement matrix with sizes in the range of micrometres to millimetres and result from imperfect placing. The second category is the capillary pores. There is a common consensus for capillary to be the remaining spaces which are not occupied by hydration products or unreacted cement grains. The volume fraction of capillary pores decreases with hydration as cement reacts progressively with capillary water to form hydrates. Thus, the size of capillary pores goes down from initially micrometres to a few nanometres in well-hydrated samples (Muller et al. 2013). The third category of pores is generally denominated as the gel pores. Gel pores are the intrinsic porosity of C-S-H hydrate (or C-S-H gel) and are considered by many authors to be part of it. Gel pores is a generic term defining all pores within C-S-H. They are nanometre-sized pores.
