Creep and relaxation of cement paste caused by stress‐induced dissolution of hydrated solid components

Abstract

The creep and relaxation of cement paste caused by dissolving solid hydration products is evaluated in this work. According to the second law of thermodynamics, dissolution or precipitation of solid constituents may be altered by the change in stress/strain fields inside cement paste via alteration of the stress power or strain energy. Thus, it is hypothesized that stress‐induced dissolution can affect the overall creep/relaxation behavior of cement composites. A novel, fully coupled thermodynamic, mechanical, and microstructural model (TM2) that uses the finite element method was developed to predict the time‐evolving properties of cement paste under prescribed strains and to test the hypothesis. In the model, the strain energy was incorporated to accurately predict the effect of stress and strain fields on cement microstructure change. From the simulation results, depending on the stress/strain levels and the choice of the domain (over which the thermodynamic equilibrium is enforced), stress‐induced dissolution of solid constituents can lead to significant creep/relaxation.

Basic creep of cement paste at early age - the role of cement hydration

“…However, the fact that the equivalent systems where the hydration-related dissolution is not active still show nonnegligible creep (the same holds for the creep response of the very old, fully hydrated systems) cannot be explained with the hydration-induced dissolution theory and hence confirms that at least part of the measured creep is due to the intrinsic viscoelastic properties of the cement-paste, which is also in line with findings of indentation studies [4,5,22]. Another hypothesis that could explain at least part of the creep visible in the equivalent systems and real systems at later ages stems from the stress-induced dissolution of hydrates, as postulated in [8,50,51].…”

“…This means that the average stress on the hydrates increases along with hydration as load is redistributed to them from the elastic unhydrated phase that dissolves. This constitutes a major difference compared to the solidification theory of creep [10], where stress carried by the hydrates decreases with Grasley et al [50] proposed based on theoretical considerations that the stress-induced dissolution of hydrated phases could further contribute to the apparent creep in hydrated systems; this approach was also supported by the simuations by Li et al [51] . Also, Pignatelli et al [8], based on some experimental evidence argued that dissolution of C-S-H due to applied stress could contribute to creep.…”

Microstructure models of cement: their importance, utility, and current limitations

“…Microstructural models have been widely used to study the development of the mechanical properties of hydrating cement pastes, mortars, or concrete. While most of the work has been limited to modelling of the paste as a linear elastic solid [8,52,53], some work on the non-linear behavior, brittle fracture [54][55][56][57], and viscoelastic/viscoplastic properties of the paste [58][59][60][61][62] is also available. Two main approaches, analytical and numerical, have been used to homogenise the properties of cement paste for these purposes.…”

MOSAIC: An Effective FFT-based Numerical Method to Assess Aging Properties of Concrete

“…There are several mechanisms that have been proposed to explain creep in C-S-H. The most common is the sliding of the aforementioned sheets with respect to each other under sustained stress (Ulm et al 1999;Alizadeh et al 2010;Tamtsia and Beaudoin 2000;Thomas 1937;Lynam 1934;Jennings 2004;Acker 2004;Vandamme and Ulm 2009a), but other mechanisms, such as dissolution under stress (Li et al 2018;Moradian et al 2018;Pignatelli et al 2016) or a change of site of a particular bond between Ca ions bridging oxygen atoms in silicate groups due to stress or thermal activation (Gartner et al 2017), have also been discussed in the literature. Additionally, creep and stress relaxation are not independent of one another and the combined viscoelastic response is termed 'creeprelaxation'.…”