Clarifying the deformation restriction of unhydrated phase in cement paste to its autogenous shrinkage

Autogenous shrinkage of cement paste depends on the competition between bulk stress (driving force) and deformation restriction (intrinsic modulus). Since the bulk stress can be calculated according to capillary theory, the deformation restriction contributed by unhydrated phase should be paid more attention due to its higher proportion and modulus. However, it is hard to trace the development of unhydrated particles distribution and time-dependent modulus in real time. To clarify the deformation restriction of unhydrated phase, cement pastes consist of nearly fully-hydrated matrix and inert fillers with targeted size and volume were prepared in the present study. Based on the bulk stress calculated by saturation degree and the modulus obtained by upscaling calculation, an empirical function was proposed to link autogenous shrinkage, internal stress, and deformation restriction of cement paste directly. Moreover, the deformation restriction mechanism of unhydrated particles was explained by the effective volume of restricted region around the unhydrated particle, and the deformation restriction can be maximized by rationally arranging unhydrated phase with volume content of 30–40% and particle size of 5–10 μm. The results provide a new sight in understanding the deformation restriction of unhydrated phase, and then lay a solid foundation to minimize the shrinkage of cement-based materials by microstructurally design of cement paste.