Mechanical and physico-chemical properties of hardened Portland cement pastes containing hydrophobic admixtures - Part 2. Physical properties and microstructure

The effect of stearic acid and corn oil as hydrophobic admixtures on the ph ysical properties (bulk density, total porosity and water absorption) as we ll as the microstructure Of the hardened Portland cement pastes was investi gated. The results showed that the hydrophobic admixtures slightly decrease the bulk density and greatly decrease the absorption of water A schematic representation of the formation of a hydrophobic layer on the surface of po res have been suggested. The results of SEM examination also showed that th e calcium silicate hydrates formed in the presence of water-repellent admix tures have a more colloidal and spongy character than C-S-H formed: in the absence of these admixtures (blank paste).