REACTION AND COMPOSITIONAL AND STRUCTURAL CHANGE OF HARDENED C_3S PASTE IN THE PROCESS OF DISSOLUTION

摘要

An obvious change of pore structure wasobserved in the hardened C_3S (C_3S:3CaO SiO_2) pastewhich was exposed in pure water for leaching test. Byanalyzing the cross section of tested sample with EPMA andSEM, degraded area was clearly discriminated from the non-degraded area. The shift of the boarder of degraded area andnon-degraded area with time (degrading front) was provedto be caused by the diffusion of Ca ion through hardenedC_3S paste. The profile of Ca ion concentration from thesurface contacting with water to bulk at the cross section ofhardened C_3S paste lead from present experiment coincidewell with the profile of diffusion model presented by Buil.Through present experiment, it was observed that not onlythe dissolution and diffusion of Ca, but also secondaryprecipitation of hydrate occurred in the degraded area. It wasconcluded that such a behavior of Ca resulted in thespreading and refilling-up of pore and the change of pore structure.