[en] Highlights: • In-situ observation made on cement paste suggested that the stress application changed the development of microstructure. • The cement grains dissolved faster under stress. • The accelerated reactions under load resulted in increase in stiffness and deformation of the samples. While the stress-induced dissolution of various minerals has gained attention as an important time-dependent deformation mechanism, this has only sparingly been investigated in portland cement systems. In this paper, X-ray Computed Tomography (XCT) is used to make direct observations of the microstructural evolution in cement paste samples under different levels of stress during their first 60 h of hydration. Stiffness and creep measurements are also made while imaging the changes in the microstructure. The results show that stress applied at ages between 24 h and 60 h caused an increase in stiffness, increase in early age creep, and a statistically higher amount of dissolution of individual particles near the point of load application.

[en] When cementitious materials are dried, internal stresses are generated that lead to desiccation shrinkage, a portion of which is irreversible. Previous research has indicated that, while a cementitious composite is subjected to a state of stress, dissolution of cement grains and precipitation of hydrates can yield irreversible creep strains, and it is hypothesized that the same process can lead to irreversible shrinkage during drying. To evaluate this hypothesis, a computationally implemented model integrating a microstructural evolution model with a finite element calculation routine was utilized. This computationally implemented model is capable of predicting the magnitude of shrinkage deformation of cement paste during drying conditions as a result of cement grain dissolution and hydrate precipitation. From the simulation results, the mechanism of cement grain dissolution and hydrate precipitation can lead to significant shrinkage behavior of cement paste, and it is also a potential mechanism resulting in the irreversible component of desiccation shrinkage at early ages (e.g., while the hydration rate is significant). The predicted irreversible shrinkage decreases with the age at which drying is initiated as a result of the decreasing hydration reaction rate.