A consolidation model for bleeding of cement paste

Abstract

Synopsis Bleeding of freshly mixed cement paste, mortar or concrete is the result of a complicated interaction between various physical and chemical forces. In this paper, a self-weight consolidation model is proposed to explain this phenomenon. This model arises from the observation that, in the usual range of water/cement ratio by volume of 10-2-0, the concentration of cement paste is high and the cement particles are expected to be in close contact with each other, thus suggesting the presence of inter-particle forces. This is akin to the concept of effective stress in soil mechanics. The existence of such forces implies that bleeding must be governed by consolidation and not sedimentation as previously thought. Two series of tests were conducted and the results compared with the theoretical predictions. The very good agreement represents an improvement over traditional sedimentation models and suggests that the bleeding phenomenon may indeed be governed by the mechanics of consolidation.