OPC hydration with highly alkaline solutions

Hydration of an ordinary Portland cement (OPC) with highly concentrated alkaline solutions has been carried out. Two different alkaline solutions were used: NaOH (10 M) and Na₂CO₃ (3·8 M). Mineralogical composition of the compounds formed after hydration process were determined by FTIR; XRD; DTA/TG. Soluble salts in water and in methanol–salicyclic acid were extracted and the amount of sodium fixed by the CSH gel was deduced. The main conclusion of this work is that if high concentration of NaOH is present in the hydrating solution, CSH gel breakdown is produced. Additionally, it has been showed that gypsum reacts with sodium producing Na₂SO₄. Finally, in the carbonation process a calcium±sodium carbonate is formed.