New models for predicting hydration and maturity development in blended cementitious systems

This study deals with multi-scale kinetics study of blended cements containing supplementary cementitious materials (SCMs). The objective is to link meso-scale hydration kinetics to macro-scale mechanical properties of concretes.; A systematic kinetics study is conducted on single-component and multi-component cementitious systems. Long-term isothermal calorimetry tests are used to record hydration rates covering three orders of magnitude starting right after mixing to 21 days at three temperatures. This new technique enables a better understanding of hydration mechanisms up to 1 month of hydration, which is important for long-term strength development and durability. Early age hydration (up to 20-30% hydration) of single-component cementitious systems (C3S and slag) can be described by the Avrami's nucleation model. Afterwards hydration is continuously slowed down, and can be modeled by a Jander type diffusion model. For more complicated multi-component ordinary Portland cements (OPC), a correction factor is introduced to the Jander's model to describe the simultaneous diffusion processes of multiple compounds. Absolute hydration rate is expressed as the product of absolute rate constant, and a function of relative hydration. This form of rate function makes it easier to evaluate the influencing factors on hydration. Activation energy is determined from the absolute rate constant, and found to be constant for nucleation and diffusion stages. The constant activation energy is explained by the fact that the same chemical reactions occur and produce the same reaction products, which can be verified by the TGA results. The absolute-rate based hydration kinetics was used to improve the conventional relative-rate based maturity functions, and to develop a computational procedure to predict hydration development under non-isothermal conditions.; A new methodology is developed to separate the contributions of SCM's pozzolanic reaction from OPC hydration. This approach facilitates the evaluation of SCM's reactivity, the optimization of blended cements, and the assessment of compatibility of SCMs with cements. An evaluation procedure is proposed by utilizing a quantitative link between compressive strength and heat of hydration established in this study. Using this procedure, only limited testing is needed to investigate blended cements, thus circumventing the cumbersome strength testing usually used in the literature.