| This dissertation is a combined experimental and model-based investigation that endeavors to illustrate new modeling strategies and offer insights into relevant latest hypothesis regarding hydration of hydraulic cement phases, tricalcium silicate (C3S), and alite. The dissertation is organized into three parts---a review of models; experimentation; and modeling.;Rather than commenting on each individually, models were sorted into four categories: (1) simple and combined mechanisms models, (2) nucleation models, (3) particle size models, and (4) simulation environments. The relationship between various models is also shown so that the evolution of the field is illustrated. The experimental part focuses on the microstructural characteristics of hydrated C3S, alite, and type I portland cement at ages between time zero and 28 days. X-ray diffraction, calorimetry, and electron microscopy-based image analysis here used to quantify the development of calcium hydroxide (CH) and calcium silicate hydrate (CSH) at micro- and meso-length scales. Easily recognizable islands of CH were found to form by three hours and were noted to influence hydration by hindering the reaction of unhydrated cement particles that are embedded within the largely CH bearing matrix. A combined technique was used to determine the stoichiometry and density of the evolving CSH during C3S and alite hydration. The findings show that the stoichiometry of hydrated alite and C3S are shown to be different. Finally, based on energy dispersive x-ray spectroscopy (EDS) analysis, it appears that the bulk density of CSH increases with time, consistent with recent hypothesis based on experiments which suggest densification.;The modeling part focuses on a semi-analytical continuum mechanical approach for approximating reaction and transport in a single C3S or alite particle was developed. Instead of using water as the transport controlling species, H2SiO4-2 was used. A continuous phase mass balance also links solution chemistry to kinetic and transport processes. The model was derived from the fundamental macroscopic and microscopic mass continuity theory. Based on the experimental observations, CSH product was densified during the hydration, forming low density product first and then growing both on the surface and in the bulk. Meanwhile, Avrami's equation was used to simulate the overlapping area for a single particle. All the parameters in the model have reasonable physical meanings and the results were shown to be consistent with the experimental data.;A new model were shown to be developed for the simulation of ensembles of particles which retains elements of nucleation and solution phase chemistry effects. A population balance framework was used to describe the individual hydration behavior of each particle in the system, adjusted only with parameters that have reasonable physical values. The simulation results reproduced all three experimental hydration stages of C3S hydration, including the induction period. |
