The effect of bleeding on ice formation and water transport in blended cement systems

The presented paper aims to investigate how bleeding affects the ice formation and transport properties of blended cement systems. Three compositions of cement paste were studied, i.e., consisting of pure Portland cement, and containing silica fume and granulated blast furnace slag respectively. The ice content along with the distance from the surface was monitored using differential scanning calorimetry. The amount of ice formed in pore system decreased along with sample depth. However, bleeding mainly affects the crystallization within the connected capillary pores occurring above -30 degrees C. It was shown that the application of supplementary cementitious materials shortens the zone affected by bleeding and reduces the ice content. The porosimetric study revealed that the porosity of cement-based materials is not homogeneous along with depth. The large pores of diameter from 200 to 800 nm, which are similar to the ones resulting from the excess water introduced to cement paste with high water-to-cement ratio, appear in the vicinity of the surface. In order to investigate this effect in concrete, the water transport properties were studied. The results of capillary rise and water permeability tests evince that the fluid movement is increased if it occurs through the surface zone.