Molecular and submolecular scale effects of comb‐copolymers on tri‐calcium silicate reactivity: Toward molecular design

Abstract

The impact of organic compounds on the processing and reactivity of inorganic materials has been a source of inspiration for materials scientists for decades and continues to trigger novel and innovative applications in a broad range of disciplines. However, molecular design of such compounds to reach targeted properties remains challenging, particularly for reactive and multicomponent systems. This outstanding challenge is met here by combining a model cement, hosting different coupled reactions of dissolution, nucleation and growth, together with combcopolymers that offer large and well-controlled variations of their molecular architecture. We show that silicate reactivity is affected by a combination of molecular and submolecular scale effects of these polymers. The first can be described by scaling laws from polymer physics, whereas the second involves specific chemical interactions. In particular, the ability of these polymers to hinder dissolution appears to be crucial, something for which strong experimental evidence is provided. K E Y W O R D Scalcium silicate,

Shifting factor—A new paradigm for studying the rheology of cementitious suspensions

“…It suggests that the polymer is only effective above a certain dosage. One interpretation is that part of the polymer is “lost” either by the formation of micelles or through a sequestration by aluminates hydrates . This may indeed occur in our study since the polymer is included in the mixing water.…”

“…As a result, the topic of rheology control has received much attention over the past years, covering theoretical understanding of flow tests, thixotropy, working mechanisms of concrete admixtures, as well as bleeding and/or segregation issues . Moreover, important progress has been made in understanding how, in relation to their molecular structure these admixtures can slow down cement hydration, a side‐effect that is most often undesired . This topic closely connects to a background motivation of this paper, which is to understand the loss of fluidity that cementitious systems exhibit over time.…”

Advances in dissolution understanding and their implications for cement hydration

“…Although controlled in any other industrial context, the in-depth analysis of the defect-reactivity relation has not been performed for alite. However, the impact of thermal treatments or annealing, supposedly reducing defect density, has clearly evidenced an effect on dissolution and hydration [3,42]. In particular, thanks to the enhanced diffusion of atoms in the crystal structure, annealing lowers reactivity through annihilating a fraction of the defects and reducing the energy of others (Figure 3a): pairing of vacancies and interstitial ions, clustering of foreign atoms, annihilation or stacking of dislocations [43].…”

“…As mentioned earlier, the surface bonding of ions [33,51] or the adsorption of polymers [42] also stabilize the alite surface and in turn extend the dormant period. Although mechanisms have not been resolved, the analogy with the hydration of annealed alite suggests a site specific interaction [42], without any impact on the subsequent acceleration rate (Figure 4b): adsorbed ions and molecules passivate the surface and block the dissolution of line defects, like dislocations outcropping at the surface, or point defects.…”

“…Monovalent ions hardly interact with C 3 S and barely show any effect on dissolution. Species with higher valences such as sulfates [33], phosphates [44] or comb-copolymers [42], which interact electrostatically with the charged C 3 S surface, are able to slow down the dissolution rate more or less effectively depending on their charge density. Covalent interactions are expected to impair dissolution more strongly: for instance, aluminum chloride significantly reduces C 3 S dissolution rate in alkaline conditions (pH12) [33], which can be attributed to the formation of covalent Si-O-Al bonds [45,46].…”