Molecular modelling of the mechanism of action of phosphonate retarders on hydrating cements

Abstract

We consider the implications of a kinetic scheme, recently proposed by Billingham and Coveney (J. Billingham and P. V. Coveney, J. Chem. SOC., Faraday Trans., 1993, 89, 3021), for the hydration of cement slurries from a molecular modelling perspective. We study a range of known phosphonate cement-setting retarders which display widely differing capabilities, and in the first part of this paper we rationalise the relative efficacies of these compounds. To do this, we deployed a range of molecular modelling techniques, including energy minimisation using semi-empirical quantum mechanical and empirical force-field calculations, for both isolated molecules and molecules interacting with appropriate surfaces of ettringite. Molecular dynamics has also been used to seek out optimal conformations of these molecules on the surfaces in question. The implications of this docking mechanism for the resulting ettringite crystal morphology are also considered.Our work provides an explanation for the relative order of effectiveness of these retarders, which is confirmed by experimental studies. We have also been able to identify a powerful phosphonate retarder on the basis of this work. Using the same modelling methods as a basis for molecular design, we propose some new phosphonate retarders which might be expected to act as effective retarders. These include novel phosphonates based on the hexaaza-18-crown-6 macrocycle. One of these exotic molecules has now been synthesised and found to display significant retardation capabilities. The synthesis of related compounds is currently in progress.

Mechanical properties of ettringite and thaumasite—DFT and experimental study

“…Calculations reproduce the mechanical properties of crystalline species such as alite, belite, and portlandite fairly well [8,9]. Structural composition and mechanical properties of various C-S-H phases were studied by means FF-based methods using Monte Carlo and/ or molecular dynamics simulations [10][11][12][13][14][15][16][17].…”

Molecular design of responsive fluids: molecular dynamics studies of viscoelastic surfactant solutions

“…For oilfield applications, for instance, they have been used to identify classes of molecular components and specific types of structure that should lead to new or enhanced performance, leading to a small number of viable options for the final experimental optimization process. One example is the use of molecular mechanics simulations to design retarders to delay the hydration of cement slurries [1]. Here the adsorption of polyphosphonate species to block potential sulphate sites on the fast-growing faces of calcium-aluminium sulphate mineral intermediates delayed the onset of crystallization and prolonged the lifetime of protective gel layers coating the cement particles.…”

First principle study towards the influence of Cd2+ on the morphology of sodium chloride

“…An approach similar to surface docking developed to predict the influence of additives on the crystal morphology has been employed here [20][21][22][23][24][25][26]. The basis of this approach is to analyze the effect of additives on the individual crystal faces, which are cleaved from a crystal.…”