Water transport in cements: A bottom - up approach based on NMR relaxation and imaging analysis and numerical modelling

Lead Research Organisation: University of Cambridge
Department Name: Chemical Engineering and Biotechnology

Abstract

Concrete is an inherently low energy input material (600-800 MJ/tonne) comparable to wood (500 MJ/tonne). However, the enormous quantities used worldwide mean that it accounts for at least 5% of global CO2 production with demand for cement set to double / treble by 2050 . Water movement in concrete is a key factor influencing the long term performance and degradation of infrastructure by both physical and chemical means. Moreover, water is a key constituent of cement, the primary binder phase of concrete. However, remarkably, there is as yet no clear understanding of pore-water interactions in cements. Equally there is no good predictor of water transport in concrete. To gain this understanding will achieve a critical step towards predicting the long-term performance of concrete and the design of new cement materials with lower cement CO2 emissions per unit of performance . To date, most approaches to the understanding of water transport in cement have been top down . Whether by experiment or modelling , cement is treated as a macroscopic material for which effective water diffusivities are either measured or calculated. It is largely an empirical science, with relatively little known to underpin the necessary assumptions about different water transport mechanisms. This programme proposes, for the first time, a concerted bottom up approach that begins with water transport in cement at the molecular (nm) level and builds to the macroscopic. At each stage, understanding gained at one length and time scale will underpin progress at the next. The goal is to develop and test a predictive model of water dynamics that can be incorporated within / bolted onto the current pre-eminent numerical model of cement chemistry and micro-structure, mu-IC, developed by Scrivener and co-workers at EPFL, Switzerland.The programme will be achieved by combining recent advances in nuclear magnetic resonance (NMR) relaxometry with equally impressive advances in numerical modelling of cement microstructure. NMR has opened an entirely new window to our understanding of pore water interactions and dynamics in cements at the nanoscale with identification of dynamics on timescales of 1 ns, 10 us and 5 ms. Advances in numerical modelling are based on advances in other spectroscopies and microscopies. Coupling the two creates new opportunity to understand, and hence create predictive capability for water transport in cements from the atomic scale upwards. This programme will be pursued in close collaboration with international collaborators leading in their fields: Professor Karen Scrivener, EPFL and Dr Sergey Churakov, PSI, Switzerland. Moreover, there is strong networking to a major intrnational cements research network of 15 industrial and 22 academic partners: NANOCEM. NANOCEM will contribute 57,000 including 35,000 cash to the programme and 22,000 for a 6 month PDRA at Surrey, up to March 2010. Project students and post-doctoral researchers will make extended visits to these collaborators.

Publications

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Etzold M (2014) Growth of sheets in 3D confinements - a model for the C-S-H meso structure in Cement and Concrete Research

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Etzold MA (2015) Filling of three-dimensional space by two-dimensional sheet growth. in Physical review. E, Statistical, nonlinear, and soft matter physics

 
Description The grant examined the meso-structure of cement. This is a hydration product, called C-S-H, which forms when water is added to cement powder. Despite its vast use and economic importance there is still debate about the structure of C-S-H on the 1-5 nm length scale. There are numerous models available for the structure but they all have difficulties explaining the observed low permeability of cement paste. One proposed model for C-S-H involves two dimensional sheets, which grow at random orientations, filling space. We have shown how such structures fit all the experimental observations for C-S- H and can also predict low permeability values. The consequence of the work in this project is in predicting lifetimes for bridges and other concrete structures which are subject to moisture.
Exploitation Route The sheet growth model has been published and there is interest in the cement community - time will tell as to how it is taken up. If successful it will allow the re-design of cement strength models. The physics side of the sheet growth model has also been published. The network model side of the work will hopefully be published soon.
Sectors Construction

 
Description The grant has finished but the student is still working on his PhD so it is a little early to be expecting the results to be being used. The Cambridge side of the project produced a sheet growth model to predict the meso-structure of C-S-H. I think this is seminal and I hope that the cement community starts to use the model in their structure property models for cement and cementitious structures.
First Year Of Impact 2014
Sector Construction,Manufacturing, including Industrial Biotechology
Impact Types Economic

 
Description Estimation of Transport Properties of Model Cement Microstructures 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Type Of Presentation keynote/invited speaker
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Workshop presentation as part of EU program.

people listened to our work
Year(s) Of Engagement Activity 2013