College Park, Maryland June 6 - 10 , 2004
T2-B1 (1:30 PM): States of Water in Hydrating Portland Cement
R. A. Livingston (Federal Highway Administration), D. A. Neumann, A. Allen, N. Nemes (National Institute of Standards and Technology)
The essential reaction in the hardening of Portland cement occurs between tricalcium silicate and water. The kinetics of this reaction are complex with up to 5 different stages, but have been characterized using neutron scattering methods. These reveal at least three states of water that are called: free, confined and chemically bound. These can be related to the conventional cement chemistry classifications of non-evaporable water, gel pore water and capillary pore water. Following these states individually as a function of temperature, particle-size distribution and water/cement ratio provides insights into the rate controlling mechanism of each stage. These can also be related to macroscopic property development in the concrete such time of initial and final set. It has been proposed that water also exists in a glassy or solid state in the hydrated cement, but this does not seem possible from thermodynamic considerations.
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