Pair distribution function analysis of nanostructural deformation of calcium silicate hydrate under compressive stress

Abstract

Despite enormous interest in calcium silicate hydrate (C-S-H), its detailed atomic structure and intrinsic deformation under an external load are lacking. This study demonstrates the nanostructural deformation process of C-S-H in tricalcium silicate (C3S) paste as a function of applied stress by interpreting atomic pair distribution function (PDF) based on insitu X-ray scattering. Three different strains in C3S paste under compression were compared using a strain gauge, Bragg peak shift, and the real space PDF. PDF refinement revealed that the C-S-H phase mostly contributed to PDF from 0 to 20 angstrom whereas crystalline phases dominated that beyond 20 angstrom. The short-range atomic strains exhibited two regions for C-S-H: I) plastic deformation (0-10 MPa) and II) linear elastic deformation (>10 MPa), whereas the long-range deformation beyond 20 angstrom was similar to that of Ca(OH)(2). Below 10 MPa, the short-range strain was caused by the densification of C-S-H induced by the removal of interlayer or gel-pore water. The strain is likely to be recovered when the removed water returns to C-S-H.