Conceptual model and test methods for fresh cement paste

The lack of robustness of SCC regarding stability is one of the main reasons for the low market share of SCC in Norway. Lots of research has been done on aggregate segregation and also bleeding has been considered. However, the stability of cement paste itself lacks understanding. Within the fresh period, sedimentation causes solid fraction differences from top to bottom, resulting in instability phenomena such as bleeding and inhomogeneity of the paste body. This paper reviews some theories on particle sedimentation and also discusses the influence of the particle size distribution, solid volume fraction and the addition of chemical admixtures and/or fillers on stability. Then a conceptual model is proposed for cement paste stability analysis. This model is verified by some hydrostatic pressure measurements and in situ sampling tests for cement pastes and limestone slurries. The experimental results are in line with the prediction of the conceptual model.