Fluid dynamics and porous media

Nano and micro porous materials are ubiquitous across many industrial sectors including construction, foods and pharma, petrochemicals and agriculture. The distribution and transport of liquids within the pore structure of these materials impacts many of the processes central to these industries.

The group carries out fundamental experimental and modelling studies of relevance to porous media. Experimental work, led by Professor Peter McDonald focuses on the development and application of a suite of nuclear magnetic resonance imaging and relaxation analysis (NMR / MRI) instruments and techniques using facilities some of which are unique to the University of Surrey. NMR and MRI are powerful, non-destructive and non-invasive techniques able to probe fluid dynamics in porous media over a very wide range of time and length scales ranging for nano-metric / pico-second to centimetres and days.

Theoretical work is led by Dr Faux. Like experiment, it too is multi-length and timescale ranging from molecular dynamics simulations of diffusion and surface adsorption at the molecular level all the way through to Lattice Boltzmann and Monte Carlo simulations of transport in complex geometries. A second and equally important strand of the theoretical work focusses on proper interpretation of NMR relaxation times of fluids in porous media with a view to learning both about the confining microstructure (pore size distribution; pore connectivity) and of the fluids within (surface wetting; surface adsorption; inter-pore exchange rates etc).

Applications work in the group focusses primarily construction materials including cements and concrete; wood (both living trees and felled timber) and, with Joe Keddie, coatings materials. Further information one each of these key themes can be found elsewhere on this site.

NMR and MRI of Cement and concrete

Concrete is the most massively produced man-made material on the planet – estimated at 4 tonnes per person per year globally. The binder of concrete is cement and the active component of cement is calcium-silicate hydrate, a highly disordered, nano-porous material. Although cement is an inherently low CO2 material, arguably as environmentally friendly as wood on a kg for kg basis, the sheer volumes involved mean that cement production is responsible for circa 5-8% of man-made global CO2 emissions. Our work seeks to impact this environmental cost and has two principal drivers. The first is that water is intimately linked to cement hydration and hardening. The second driver is that water transport underlies nearly all forms of concrete degradation.

Consequently, current work is directed towards understanding the nano-scale morphology and water dynamics in cement with a view to enabling predictive incorporation of supplementary cementitious materials with lower CO2 impact. The group was the first to identify and measure the exchange of water between nano-scale gel pores in cement, has more recently proposed a quick and efficient means to characterise the C-S-H morphology, density, composition and pore size distribution using widely available bench top NMR equipment and most recently has shown how cement microstructure is dynamic and changing in response to water drying / ingress. At the other end of the scale, a portable MR system for the in-situ characterisation of the curing and degradation of concrete in the built environment has been developed undergone “field-trials” in Germany and UK.

The group works closely with members of the industry / academic Nanocem consortium (www.nanocem.org) providing much of the NMR / porous media know-how input into, and an increasing fraction of the modelling work that is going on in that consortium. Work has been and / or is currently funded by the UK Engineering and Physical Sciences Research Council (EPSRC); The Royal Society; Industry and the EC. In particular the EC H2020 Marie Sklodowska-Curie Initial Training Network ERICA – Engineered Calcium Hydrates for Applications – that is funding 13 research students (4 in Surrey) is managed by Surrey.

D NMR T2 nuclear spin-spin relaxation time spectrum

D NMR T2 nuclear spin-spin relaxation time spectrum reveal the nano-scale inter-pore exchange of water with the C-S-H of saturated cement.

Trans-portable MRI

The group has developed a trans-portable MRI, used here to assess the curing of concrete slabs during construction of a swimming pool.

Lattice Boltzmann simulation

A Lattice Boltzmann simulation of the capillary adsorption of liquid water (black) and vapour (grey) into a model cement microstructure used to model the adsorption isotherm and transport phenomena.

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The Soft Matter Group
University of Surrey