Determination of the neutron scattering contrast of hydrated Portland cement paste using H2O/D2O exchange

Accurate measurements of the surface area of cement based materials using small-angle neutron scattering (SANS) require determination of the neutron scattering contrast between the C-S-H gel and H2O. Because the C-S-H gel has a poorly understood structure and a variable composition, calculated values of the C-S-H:H2O neutron scattering contrast based on an assumed C-S-H chemical composition and density are subject to error. The C-S-H:H2O neutron scattering contrast was determined experimentally by measuring the change in apparent surface area as the H2O in a hydrated cement specimen was replaced with D2O, resulting in a new value of 6.78 x 10(28) m(-4). This new contrast value increases some previously reported SANS surface area values by 21%. The results also confirm that C-S-H interlayer water should be included in the solid phase whereas gel pore water should be excluded. (C) 1998 Elsevier Science Ltd.