When the C-S-H gel is exposed to atmospheric carbon dioxide, it undergoes a rapid carbonation and white/yellow efflorescences appear at the surface of concrete. When the relatively fluid alkali gel continue to exude below the hardened superficial gel layer, it pushes the efflorescences out of the crack surface making them to appear in relief. Because the gel drying and carbonation reactions rates are faster than the gel exudation velocity (liquid gel expulsion rate through open cracks), in most of the cases, fresh liquid alkali exudates are not frequently encounterered at the surface of civil engineering concrete structures. Decompressed concrete cores can sometimes let observe fresh yellow liquid alkali exudations (viscous amber droplets) just after their drilling.