Chemical transformation behavior of cement hydrates deteriorated by low concentration acid

This study measured the amount of the solid phases in the hardened cement specimens immersed in pH2.0 sulfuric acid solution, hydrochloric acid and mixed acid (sulfuric acid : hydrochloric acid = 2:8 and 8 : 2 in molar ratio) in order to discuss the chemical transformation behavior of cement hydrate deteriorated by these acids. As a result, it is obvious that the cement hydrates deteriorate due to the dissolution of Portlandite by the action of proton as well as the chemical alteration of AFm phase by the action of anion. In case of the sulfuric acid acted, Monosulfate and Monocarbonate transformed into Ettringite by the action of SO₄^2- which permeated from the outside solution. On the other hand, in case of the hydrochloric acid acted, Monosulfate transformed into Friedel's salt via Kuzel's salt by the action of CI^- which permeated from the outside solution. Furthermore, in case of the mixed acid, Monosulfate and Monocarbonate preferentially transformed into Ettringite instead of Kuzel's salt or Friedel's salt. As a result, in the case of mixed acid, it was shown that CI^- may permeate to the depths more compared with the case of HC1 independently since the amount of fixation of CI ^- near the exposed surface becomes small by generating of Ettringite.