Abstract
The effect of introducing chloride into the mixing water of an ordinary Portland cement and a sulphate resistant Portland cement (SRPC) has been investigated over a range of hydration times. A simplified system of C3A, CaSO4 and Ca(OH)2 was also studied to facilitate clarification of results. A further investigation involving exposure of hardened cement pastes to chloride solutions was studied over a range of exposure times. The hexagonal β-monochloroaluminate corresponding to the formula 3CaO.Al2O3.CaCl2.10H2O has been identified by X-ray diffraction (XRD) in both sets of experiments; semiquantitative studies using XRD and thermogravimetry show increasing amounts of chloroaluminate formation with time. From the system using C3A, CaSO4 and Ca(OH)2 it was clearly shown that chloroaluminates do not form in the presence of sulphate ions. The order of preference of formation was found to be ettringite > chloroaluminate > monosulphate.
MST/759
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