The microstructure of dispersed and non-dispersed fresh cement pastes — New insight by cryo-microscopy

This study aims to give new insights to the microstructural development of fresh cement pastes without and with polycarboxylate-type (PCE) of superplasticizers. Qualitative comparisons of the particulate structure of such cementitious systems were carried out by using cryo-FIB and cryo-SEM techniques. The natural structure of fresh cement pastes was preserved by high pressure freezing. It is illustrated that non-dispersed cement systems tend to form hydration rims on the surface of the clinker grains immediately after mixing. This leads to an interlocking of the particles. In contrast, in the dispersed systems the early hydrates precipitate in the pore solution and thus, agglomeration is prevented. These microstructural observations are important aspects of the fluidization effect of superplasticizers.