The Collaborative International Dictionary of English v.0.48:

Concrete \Con*crete"\, v. i. [imp. & p. p. Concreted; p. pr &
   vb. n. Concreting.]
   To unite or coalesce, as separate particles, into a mass or
   solid body.
   [1913 Webster]

   Note: Applied to some substances, it is equivalent to
         indurate; as, metallic matter concretes into a hard
         body; applied to others, it is equivalent to congeal,
         thicken, inspissate, coagulate, as in the concretion of
         blood. "The blood of some who died of the plague could
         not be made to concrete." --Arbuthnot.
         [1913 Webster]