Models of fresh paste structure

One would expect the final distribution of cement particles after mixing is complete to be reflected in that of the hardened paste, which can be more readily studied, but no studies on the relations between mixing conditions and hardened paste structure appear to have been reported. 

To an extent that increases with the w/c ratio, fresh cement pastes exhibit the phenomenon of bleeding, i.e. settlement of the solid particles. The interparticle attractions are sufficiently strong that particles of all sizes settle at the same rate, typically about 2pms . Settlement also tends to increase the w/c ratio at the top and to decrease it at the bottom of the sample. It decreases with increased fineness or increased early hydration rate of the cement. In a concrete, it can produce layers of water beneath aggregate particles or reinforcing bars. 

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