Modelling of chemo-mechanical behaviour of low pH concretes

A model of the chemo-mechanical evolution of low-pH cement is clarified in order to be used at a structural scale. The proposed phenomenological model is based on a multiphasic hydration model developed in previous studies to predict the risk of early age cracking of structures cast with blended cements. At later ages, the evolution of mechanical properties cannot be explained only by the pozzolanic reaction usually considered in hydration models (because portlandite is entirely consumed at early ages). At these ages, mineralogical analyses showed that the hydration of remaining anhydrous silicate continued to develop by consumption of calcium from hydrates with high C/S ratios (e.g. C-S-H produced by clinker hydration at early age). A model able to predict these chemical evolutions is thus proposed. It is based on the principle of chemical equilibrium between the solution and the solid phases in terms of calcium concentration. The impact of this chemical evolution on mechanical properties can then be predicted with a better accuracy than with a classical hydration model. Finally the chemo-mechanical model is applied to the prediction of cracking of a large concrete element cast with a low pH based concrete.