Thermogravimetric investigation on the chloride binding behaviour of MK–lime paste

The hydration products of 2.5, 5 and 10% Cl− containing metakaolin (MK)–lime pastes are compared with the same obtained from MK–lime paste to understand the chloride binding behaviour of MK during the hydration of cement. Results indicate that 2.5% Cl− addition into the MK–lime paste initially enhances the formation of Friedelʹs salt (Ca2Al(OH)6Cl·2H2O), but Friedelʹs salt decomposes at later stages due to the formation of stratlingite (C2ASH8). In 5 and 10% chloride containing pastes, Friedelʹs salt is observed throughout the reaction periods along with the high amount of CSH. Small amount of stratlingite is also formed on or after 60 day hydration of 5% Cl− containing MK–lime pastes. On the other hand, MK–lime-10% Cl− containing pastes show the complete absence of stratlingite and C4AH13 through out the hydration period, which are the major hydration products of MK–lime paste. Mesuarements of pH of the simulated pore fliuds help to understand the decomposition behaviour of Friedelʹs salt. From the experimental results, chloride binding mechanism of MK–lime paste is also discussed.