The reaction between cement and natural waters containing dissolved carbon dioxide

Water regimes are known to vary markedly in their aggressivity towards cement. It has long been appreciated that the damaging regimes are associated with the presence of dissolved CO₂, Historial efforts to correlate cement performance with groundwater compositions are reviewed, especially in respect of CO₂ behaviour, as functions of its ‘aggressive’ and ‘non-aggressive’ speciations. The basic physical chemistry of the relevant aqueous solutions is explored, leading to new definitions of aggressivity and a computer-based iterative method of solving the necessary equations. Interpretation of the results is complicated by the formation of passivating layers of CaCO₃ and SiO₂ (gel) at the cement-water interface. These factors are explored and ‘coverage mapping’ is developed as a guide to their likely protective value. The model is related to dynamic situations; for example, the process of crack reheating which can occur spontaneously in concrete.