The penetration of chlorides into hardened cement pastes

The penetration of chloride ions into hardened cement pastes (hcp) has been measured by chemical analysis, X Ray diffraction and thermal analysis. The penetration of chloride depends on the permeability; thus the greater the w/c ratio the greater is the penetration.The concentration of chloride in the hcp is dependent on the concentration of the sorrounding solution.The chloride ions react with the anhydrous tricalcium aluminate in the unhydrated cement left in the hcp but not with the complex hydrated calcium aluminate salts including ettringite.Calcium mono-chloroaluminate hydrate is formed, but not all the chloride which penetrates reacts to form this mineral. The quantity of chloroaluminate formed is independent of the chloride concentration in the hcp.From a study of the pore size distribution of the hcp by mercury intrusion porosimetry it is deduced that the penetrating chloride reduces the sizes of the small pores thus reducing the permeability.