Research On The Cracking Tendency Prediction Of Early-age Restraint Cement Mortar Ring Based On The Viscoelastic Constitutive Relation

The cementitious materials change volume tremendously in its early-age stage due to moisture variation, temperature variation, and chemical reaction. Compared with the mortar, the coarse aggregates and steel bars show less variation in physical state and volume, which finally turn to be the restraints of volume deformation, especially shrinkage deformation of the martar.As is well known, the concrete’s tensile strength is quite lower than its compressive strength, and the concrete structures are tending to cracking if the tensile strength is outnumbered by the residual tensile stress, which would bring negative influence on its using function and durability.The restrained ring test has recently become a well accepted method to assess a mixture’s sensitivity to restrained shrinkage cracking. In this paper, we take the cement mortar as the research object, as the cracks are usually found inside of the mortar or on the interface between the mortar and the coarse aggregates. The mortar ring is restrained by the internal steel ring to simulate the restriction by the coarse aggregates, the steel bars, and the adjacent components during the hydration process.Further more, taking notice of the temperature variation caused by the hydration reaction and the distinct viscosity performance of early-age mortar, A thermal viscoelastic constitutive relation is needed to describe the mechanical properties of early-age cement mortar rather than the elastic or ela stic-plastic constitutive relation. For this reason, a reference to the laws of thermodynamics which the material should obey under stress will be given in this paper. Afterwards, a simple way to establish the thermal viscoelastic constitutive equation and to calibrate related parameters of the early-age mortar is introduced in this paper.Finally, in order to find out the changes of the stress development along the age of the mortar, a method to analyze the time-dependent stress considering the coupling effects of thermal, restraint, creep, and shrinkage is established based on the ―correspondence principle‖. After that, comparing the analysis results with the splitting strength measured in early-age mortar tests, a cracking tendency prediction model of early-age restraint mortar ring is proposed to help assessing or estimating the degree of cracking risk of early-age mortar ring.