Experimental study of the hydro-chemical coupling inside maturing concretes: effect on various types of shrinkage

The concrete cover has to protect the reinforcement of structures and therefore must withstand environmental damage. This resistance is clearly linked to the degree of hydration of the concrete, that is the proportion of hydrates produced from cement and mixing water. Natural drying of a structure, when forms are stripped, leads to and evaporation of free and adsorbed water and to the reduction of hydration in the external layers. The resulting hydration gradient has been determined by means of thermogravimetric analysis of samples taken from drying test bars in a controlled atmosphere (20 degrees C, 50% relative humidity). At the same time the hydration and drying effects were measured: evolution of the air's relative humidity inside the cavities of the test bars at various distances from their dried surface. Hygrothermal probes were used for this purpose. evolution of autogenous and total shrinkage and consequently of drying shrinkage. Drying and autogenous shrinkages have been linked to weight loss and internal relative humidity, respectively. These correlations can be justified theoretically.