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Identifying the Fluid-to-Solid Transition in Cementitious Materials at Early Ages Using Ultrasonic Wave Velocity and Computer Simulation

This paper assesses that the fluid-to-solid transition in cementitious systems at early-ages is crucial for scheduling construction operations, for determining when laboratory testing can begin, and for assessing when computer simulations of restrained stress development should be initiated. This transition has been traditionally assessed using mechanical penetration techniques, which, though easy to perform, do not directly relate to the evolution of fundamental material properties or the microstructure. This paper assesses the fluid-to-solid transition of a cementitious material at early ages using measures that relate to the formation of a solid-skeleton in the material. The increase in the ultrasonic wave velocity is correlated to the percolation of a solid structure that occurs during the fluid-to-solid transition. The results of computer modeling (using CEMHYD3D) indicate that solidification as determined from the percolation of the solids is similar to experimental observations (Vicat test). It is noted that the rate of change in the pulse velocity is not a rigorous method for assessment of the time of solidification, especially in systems containing air. Rather, an increase in the pulse velocity beyond a threshold value appears to be a more appropriate method to assess structure formation. Further, the isothermal calorimetry (heat release) response is observed to not correspond to a fundamental aspect related to solid percolation or structure formation in the material.