Settling of Particles in Fresh Cement Pastes

Critical comparison of the results of previous experimental studies of the settling of cement pastes at different water‐cement ratios exposed inconsistencies in published theories. Development of a γ‐ray densitometer made it possible to measure the change in density of columns of freshly prepared cement paste with time of settling in containers of clear poly(methylmethacrylate) plastic. Paste density increased at all levels in the columns; the changes were greater at the greater depths, suggesting that the settlement was developing in compression. After the rates of hydration contraction occurring within the pastes were corrected for, the initial velocities of settlement of the solids at the tops of the columns satisfied the Kozeny‐Carman equation.