Author: Alastair Marsh -
It’s always nice to receive an invitation to a talk – but especially on those rare occasions when you are asked to be on the stage rather than in the audience! Following an article I wrote in Materials World magazine, “Building out of Poverty”, the West of England Metals and Materials Association (link) (WEMMA) invited me to elaborate on the subject for a lecture in their 2017-18 programme. I was only too happy to accept, and enjoyed a stimulating hour with an audience at the University of Exeter last month (slides are available here).
My main argument was simple – research on construction materials should be focussing on the developing countries’ market, as this is where the lions’ share of both population growth and economic growth will be over the next few decades.
As well as sating engineers’ thirst for a challenge, there are strong moral arguments for this focus. The more cheaply that adequate quality housing can be built in least economically developed countries (LEDCs), the quicker that these populations can enjoy the associated improvements in wellbeing. The lower carbon intensity this can be achieved with (alongside other environmental impacts), the better chance we stand of keeping average global temperature rise <2C.
However, construction is never simply a technical matter. The informal sector tends to dominate the construction section in urban areas of LEDCs. This typically means self-builds, made with a spectrum of traditional to modern materials, and often of inadequate quality in both structural robustness and internal environment. Given its spatially distributed nature, lack of division of labour and absence of corporate players, innovation and adoption of new materials in this sector is a very different prospect compared to the formal sector in countries like the UK. For more detail, I wrote this article as a summary for material designers.
This situation calls for materials that meet several demands. They must be affordable, robust, sustainable and aspirational. None of the walling materials currently most used in this context (concrete blocks, fired clay bricks, wattle and daub) meets all these demands. My PhD research investigates a promising material, which could possibly meet these demands: geopolymer-stabilised soil materials (GSSM). By adding an alkaline activating solution to naturally occurring sub-soils, and then curing at low temperature (70-100 C) we can make a geopolymer phase – a kind of cementitious material. This phase stabilises the remaining soil, making a composite material with much improved robustness over naturally occurring soil - but retaining many of the environmental benefits.
However, the viability of this process is currently not easy to predict for different soils, given variations in clay content, the types of clay minerals present, and the other components in soil. In my PhD research, I seek to first understand how the geopolymerisation reaction compares for individual clay minerals in isolation. This gives a base of understanding from which to increase the complexity by making ‘artificial soils’ of mixtures of clay minerals, and seeing if these match the behaviour of real soils. My aim is to answer this question: is GSSM a material technology that will be viable for a wide range of soil types, over different regions of high population growth? Or, will it only be a fringe player?
As I enter the final year of my PhD, my instinctive feel is that it is the latter. Although some soils work very well with this technology, the parsimonious, conservative approach of construction (in both the formal and informal sectors) is generally to choose whatever optimises for cheapness, simplicity, and reliability. In these stakes, concrete and fired brick will likely always win – unless global policy on carbon emissions changes the cost balance to a significant degree.
Nonetheless, I would encourage all researchers (especially those in the wealthier nations of the West) to think critically about what to research, and why. Have you been asked the Hamming Question before? “What is the most important problem in your field?”. Whatever the answer, the follow-up question is then, “So why aren’t you working on it?”. This is a tricky question itself. Do we measure importance in terms of our fundamental understanding? Or ability to improve human wellbeing? Or a combination of both? Watch this space - more to come on this topic over the coming year…
My thanks go out to Gill Wheeler at WEMMA for the invitation, and to Dr Yanqiu Zhu at the University of Exeter for hosting.