STUDY OF THE STRENGTH OF VERY YOUNG CONCRETE AS A FUNCTION OF THE AMOUNT OF HYDRATES FORMED - INFLUENCE OF SUPERPLASTICIZER

The strength of microconcretes has been measured at the end of mixing and for some hours afterwards. At the same time, measurements of the heat of hydration have been made. During the 'dormant period' the hydration, slight as it is, produces in fact an increase in strength: the flocculated structure of the fresh cement paste can explain the immediate reinforcement of the bonds as soon as hydration begins. When a superplasticizer is used, besides the well-known hydration delay, the beginning of hydration does not signify now that the strength increases: no doubt this is a consequence of the dispersion of the structure by the admixture. After the setting, the filling of pores is easier with a dispersed structure than with a flocculated one, because of the better distribution of the cement particles: a sample with superplastizcier, to attain the same strength, will need less hydrates than a plain sample.