Assessing the fluid-to-solid transition in cementitious systems at early-ages is crucial for scheduling construction operations, determining when laboratory testing can begin, and for assessing when computer simulations of shrinkage stress should begin. This transition has been traditionally assessed using penetration techniques (e.g. the Vicat tests), 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 which 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 which occurs during the fluid-to-solid transition. Results of computer modeling (using CEMHYD3D) indicate that solidification as determined from the percolation of the solids is similar to experimental observations (Vicat tests). It is noted that the rate of change in the pulse velocity is not a rigorous method for assessment of the time of solidification. 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 conduction calorimetry response is observed to not correspond to a fundamental aspect related to solid percolation or structure formation in the material.
Proceedings Title: Transition from Fluid to Solid: Re-examining the Behavior of Concrete at Early Ages
Volume: SP 259-05
Conference Dates: March 15-19, 2009
Conference Location: San Antonio, TX
Conference Title: American Concrete Institute Spring convention
Pub Type: Conferences
Solidification, setting, degree of reaction, stress development, Vicat test, shrinkage