Hydration of Portland cements in solutions containing high concentration of borate ions: Effects of LiOH

The hydration process of Portland cement in solutions containing high concentration of borate ions is studied. The mechanism of retarding effects induced by borate ions on Portland cement is investigated and a solution for mitigating these effects is proposed by adding LiOH into the cement paste. Formation of a loose covering layer rich in borate around C-S-H nuclei and the consequent prevention of C-S-H growth is found to cause the strong retarding effects of borate ions at early ages. Adding LiOH accelerates the early age hydration of Portland cement with borate, and increases the compressive strength of the hardened paste. The LiOH promotes the dissolution of the covering layer on the C-S-H nuclei, and hence counteracts the retarding effects of borates on hydration of Portland cement.