Understanding cement hydration of cemented paste backfill: DFT study on water adsorption at tricalcium silicate (111) surface

New paper published on Minerals

Paper Title: Understanding cement hydration of cemented paste backfill: DFT study on water adsorption at tricalcium silicate (111) surface

Authors: Chongchong Qi, Lang Liu*, Jianyong He, Qiusong Chen, Li-Juan Yu,  & Pengfei Liu

Abstract: Understanding cement hydration is of crucial importance for the application of cementitious materials, including cemented paste backfill. In this work, the adsorption behaviour of a single water molecule on an M3-C3S (111) surface is investigated using density functional theory (DFT) calculations. The adsorption energies for 14 starting geometries are calculated and the electronic properties of the reaction are analysed. Two adsorption mechanisms, molecular adsorption and dissociative adsorption, are observed and six adsorption configurations are found. The results indicate that spontaneous dissociative adsorption is energetically favoured over molecular adsorption. Electrons are transferred from the surface to the water molecule during adsorption. The density of states (DOS) reveals the bonding mechanisms between water and the surface. This study provides an insight into the adsorption mechanism at an atomic level, and can significantly promote the understanding of cement hydration within such systems.

Keywords: Cement hydration; Tricalcium silicate; Surface adsorption; Water; Density functional theory.

Reviewer 1: The present paper deals with the water molecule adsorption on (111) surface of tricalcium silicate (C3S) using the DFT technique. The authors calculated the adsorption energies for 14 starting geometries and determined the electronic structure of water-adsorbed C3S surface and water molecule configurations. It is entirely appropriate for Minerals. I basically agree with significance of the paper. The following two points should be considered prior to publication.

Reviewer 2: Manuscript describes DFT study on a single H2O molecule adsorption on the (111) surface of tricalcium silicate, C3S, the most reactive component in cement. The authors investigated 14 initial structures of water adsorption on 7 various sites, including monodentate and bidentate adsorption modes. These 14 initial structures converged to 6 sorption complexes, 4 complexes with molecular sorption and 2 with dissociative sorption. The latter includes water dissociation while sorbing on the (111) surface. The authors performed charge analysis together with partial DOS analysis. Dissociative mechanism of water adsorption was found to be preferred over molecular one. Water is adsorbed via surface Ca ions, charge transfer is claimed from the water molecule to the surface (which is wrong!). I do not think that this paper can be published in Minerals.

Reviewer 3: The present submission investigates calcium silicate-hydrate surface chemistry using by means of atomistic modeling.

 The here investigated mineral phases are key components of mineral binders and the molecules investigated as adsorptive determine the chemical and, hence, mechanical stability of cement and concrete. For these reasons, this contribution is of high relevance for 'Minerals'.

 The study is technically very good. All theoretical methods were employed in an adequate way and corresponding results are sufficiently discussed.

There are some concerns and recommendations about the way the results are presented and this paper is written.

Reviewer 4: Nice paper. Needs some edits as commented in the annotated paper.

Graphic Abstract:

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