Chemo-physical modeling of cement mortar hydration: Role of aggregates

Abstract

International audienceAfter mixing of the cement with water, most of the anhydride products sustain the hydration process and this leads to the hydrate products, e.g. CSH, Ca(OH)2, Afm and Aft. The mentioned hydration process is a highly complex phenomenon involving the chemically based thermo-activation inside the cement mortars during the early age hydration process. The chemo-thermal hydration reactions drasticaly increase at the early age of hydration after the mixing action and then it becomes less important and turns to be nearly asymptotic. The progress of the hydration phenomenon drives the material properties change during the very early age of cement hydration. Regarding the mortar and concrete, such hydration process would not be homogeneous through the cement matrix due to the aggregates presence. These inclusions will affect the temperature distribution as well as degree of hydration. In the current contribution, the chemical and thermal hydration have been firstly investigated by means of SEM observations using replica method and secondly by the 3D-FEM numerical experiments including two different case studies using glass beads as aggregates. The numerical experiments match fairly good the experimental measurements obtained using a pseudo-adiabatic testing setup for the case studies herein. The scanning electron microscopy (SEM) images observation demonstrates the gap spaces around the glass beads next to the external surfaces. These gaps can be essentially seen for the multi-glass beads case study. The role of the temperature and degree of hydration gradients are clearly obtained using the numerical samples. Some fresh routes and outlooks have been afterwards discussed

Why does the modified Arrhenius’ law fail to describe the hydration modeling of recycled aggregate?

“…Basically, the larger hydration gradient values deal with the greater gap spaces. As seen in Figure 11, despite the fact that the temperature and degree of hydration distributions are quite uniform, the hydration gradient draws non-homogeneous distribution 7 . Indeed, the hydration gradient takes into account either the chemo-thermal features or the grain size and its distribution known as granulometry.…”

“…Despite the fact that most research studies deal with the physical properties variation as indicated earlier, the 3D hydration phenomenon analysis about the recycled-sand-based mortars has not been studied yet [5,6]. According to the recent study [7,8], the modified Arrhenius' law can be used to estimate the degree of hydration on the two-phase mortars as well as the hydration gradient around the aggregates 1 . Furthermore, the ITZ zone where the gap space next to aggregate is always observed, is highly linked to the gradient hydration, i.e.…”

“…In the previous studies [7,8], the effect of the grains and their so-called diffusive impacts through the cement paste matrix are demonstrated using the direct multi-physics coupling via the finite element method. According to the above-addressed contributions, the heterogeneous hydration gradient and its stiffness evolution have been found out through the cement paste including the glass beads and aggregates [7,8]. Hence, the aggregates role on the hydration process and more importantly the natural aggregates and recycled aggregates will be studied via the experiments and numerical modeling.…”

“…• Gradient hydration The gradient of hydration concept is very essential tool in determining the gaps creations around the grains and cement paste during very early age and early age [7,8]. Basically, the larger hydration gradient values deal with the greater gap spaces.…”

Non-linear elastic micro-dilatation theory: Matrix exponential function paradigm

“…the cement-based materials (Scherer, 1999;Flatt, 2002;Scherer, 2004;Flatt and Scherer, 2008) and porous masonry rocks including and excluding moisture transfer (Chéné et al, 1999;Ramézani and Jeong, August 2011). The coupling of the micro-dilatation theory of the reactive materials would be also of great interest (Jeong et al, 2013a;Jeong et al, 2014). 4.…”