Modeling of volume changes of concrete mixed with expansive additives

•We modeled volume changes of concrete mixed with expansive additives.•Shrinkage was modeled by considering the behavior of the moisture in pore.•Expansion was modeled by considering the volume increase rate of hydrates.•Volume changes modeled by considering a balance of cement and expansive additives.•Volume changes of concrete could be estimated sufficiently by using a composite model. This study modeled volume changes of concrete mixed with expansive additives, a countermeasure to shrinkage. Volume changes of expansive paste are determined from the balance between the shrinkage of cement and the expansion of the additives. Therefore, in this study, volume changes were modeled by applying a balance to the hydrates of cement and the expansive additives. The shrinkage of cement was modeled by assuming that it is caused by capillary tension. This modeling was based on the behavior of the moisture inside the cement’s pore structure, by taking into account the pore size distribution and the thermodynamic equilibrium state of the moisture. Using the concept of effective radius factor, the expansion of the expansive additives was modeled by considering the volume expansion of the additive particles caused by an increase in the outermost radius of particles of the hydration products that were formed at an early age. The values predicted by the model were consistent with the measured values, which confirms the model’s validity. Furthermore, the volume changes of concrete were estimated with sufficient accuracy by analyzing the behavior of the paste using a composite model of aggregate and paste.