Ultrasonic propagation through hydrating cements

Hydraulic cements develop mechanical strength and low permeability as a result of hydration, which involves chemical reactions between water and the anhydrous compounds present in the cement. Solid hydration products form both at the surfaces of the cement particles and in the pore space by nucleation and aggregation. As a result, the solid phase becomes highly connected and the material transforms from a viscous suspension of irregularly-shaped cement particles into a porous elastic solid with non-vanishing bulk and shear moduli. This transition to an interconnected solid phase is an example of a percolation transition. In this paper, measurements of the velocity of ultrasonic longitudinal and shear waves in ordinary Portland cement undergoing hydration are reported. The cement slurries were prepared in accordance with the American Petroleum Institute (API) specification for class G oil-well cement with various additives. After the time at which the cement becomes interconnected, the effective bulk and shear moduli are found to be linearly related and the effective Poisson’s ratio is observed to decrease from the value of 0.5, characteristic of a fluid, to values characteristic of a porous elastic solid.