Juraj Šipušić

Porosity–strength relation in calcium aluminate cement pastes

Abstract The compressive strength and the volume porosity of calcium aluminate cement pastes have been studied in order to connect their relationship. The influence of mass fraction of lithium carbonate on compressive strength and porosity of calcium aluminate cement (CAC) has been investigated at different water–cement (w/c) ratios. The functions proposed in the literature for different technical materials were tested on obtained strength and porosity data. Those functions have been a base for further development of more general functional dependence of strength and porosity for cement materials. Thus, we propose the following equation to relate the strength and porosity for CAC pastes: σ=σ P 0 1− P P 0 2

A new approach to solid-state reactions kinetics analysis: the application of assisting functions to basic equations for isothermal conditions

Abstract Functions describing simple models for solid-state reaction kinetics under isothermal conditions were transformed in order to obtain new functions with improved properties suitable for kinetic analysis. The transformations were performed trough multiplying well known functions as Johnson–Mehl–Avrami or Jander’s with assisting functions. In such manner, new functions, Φ , were obtained enabling calculation of kinetic parameters in a simple way. The relationships between the values of the extremes of Φ functions and various kinetic parameters have been established. The calculation of kinetic parameters by application of new equations have been demonstrated on six model systems. Very good agreement between preset and calculated parameters for each model system has been observed. Using the same approach, the rate-determining step, i.e. the reaction model, and proper kinetic equation could also be determined.