Effect of applied stress on the helium inflow characteristics of hydrated portland cement

Studies of porous hydrated portland cement have been carried out to assess quantitatively some aspects of microstructural deformation due to applied stress. Hydrated portland cement paste cured for six years at a water/cement ratio of 0.6 was sliced into discs 1.25 mm thick. These were positioned in a specially designed sample holder and loading device that permitted the specimens to be placed under uniaxial compressive stress at 7.1, 14.8 and 22.8 MPa. Helium intake and pycnometric measurements were made at 0, 2.5, 4.5, 7.0 and 9.0 per cent moisture loss with respect to the 11 per cent RH condition. Maximum effects were observed at 7.0 per cent moisture loss, at which helium intake was reduced by 48 per cent at 40 h. Densities were also reduced by stress, and it was concluded that entrances to interlayer space were constricted during application of stress.