Shear and viscoelastic properties of early-age concrete using small-amplitude and low-rate rheometry – From fresh state to initial set

Abstract

The advancement of concrete technology such as 3D concrete printing has rekindled research interest in the early-age mechanical properties of concrete. However, the non-adaptability of early-age (plastic) concrete to classical mechanical measurements causes the quest for alternative approaches. This study is a new and unique approach, using rheological methods, aimed at investigating the early development of shear and viscoelastic properties of concrete from the time of mixing up to the initial setting time. Dynamic shear rheometry (coupled with rotational tests), taking advantage of the normal stress measurement, was used to evaluate the shear and viscoelastic properties. Viscosity modifying agent (VMA), superplasticiser (SP) and increased water content were incorporated to achieve a robust test program. The Mohr-Coulomb shear parameters, shear yield parameters, shear modulus, creep and stress relaxation properties were evaluated from rheometry tests. Theoretical and experimental analyses of a vane-in-cup rheometry reveal that the resultant normal stress, during an elastic response, originates from the self-weight of the sample and is dependent on the sample's weight distribution. The results, therefore, show that it is not sufficient to estimate the self-weight of the concrete for normal stress evaluation and that the shear and creep properties of concrete mainly develop within half-time of the initial set while stress relaxation is inherent and remains fairly unchanged. Challenges and prospects of this approach were also discussed.